@article {657, title = {Bilirubin oxidase-based silica macrocellular robust catalyst for on line dyes degradation}, journal = {Enzyme and Microbial Technology}, volume = {120}, year = {2019}, month = {Jan-01-2019}, pages = {77 - 83}, abstract = {

We present a new heterogeneous biocatalyst based on the grafting of Bilirubin Oxidase from Bacillus pumilus into macrocellular Si(HIPE) materials dedicated to water treatment. Due to the host intrinsic high porosity and monolithic character, on-line catalytic process is reached. We thus used this biocatalyst toward uni-axial flux decolorization of Congo Red and Remazol Brilliant Blue (RBBR) at two different pH (4 and 8.2), both in presence or absence of redox mediator. In absence of redox mediators, 40\% decolorization efficiency was reached within 24 h at pH 4 for Congo Red and 80\% for RBBR at pH 8.2 in 24 h. In presence of 10 mu M ABTS, it respectively attained 100\% efficiency after 2h and 12h. We have also demonstrated that non-toxic species were generated upon dyes decolorization. These results show that unlike laccases, this new biocatalyst exhibits excellent decolorization properties over a wide range of pH. Beyond, this enzymatic-based heterogeneous catalyst can be reused during two months being simply stored at room temperature while maintaining its decolorization efficiency. This study shows that this biocatalyst is a promising and robust candidate toward wastewater treatments, both in acidic and alkaline conditions where in the latter efficient decolorization strategies were still missing.

}, issn = {01410229}, doi = {10.1016/j.enzmictec.2018.10.004}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0141022918303466}, author = {Roucher, Armand and Roussarie, Elodie and Gauvin, R{\'e}gis M. and Rouhana, Jad and Gounel, S{\'e}bastien and Stines-Chaumeil, Claire and Mano, Nicolas and Backov, Renal} } @article {673, title = {Bitumen@SiO2 core-shell particles green synthesis towards flowable powdered bitumen and their binder applications}, journal = {Colloids and Surfaces A: Physicochemical and Engineering Aspects}, volume = {570}, year = {2019}, month = {Mars-20-2019}, pages = {531 - 543}, abstract = {

Mineralization of occulated bitumen emulsions allows producing bitumen powders, also referred to as Bitumen@SiO2 hybrid particles, that can resist storage in hard conditions, with a load up to 8 kPa at 50 \°C during 20 h, without alteration of their morphology or release of their bitumen core. Thanks to the occulation, nal Bitumen@SiO2 powders are not highly pulverulent and allow transportation and handling of bitumen at ambient temperature without the need of water as it is the case for bitumen emulsions. This \“water free\” storage par- ticularity exhibits the double advantage of reducing the cost of transport and of avoiding inhibition of bitumen adhesion at mineral aggregates through the presence of water, therefore rendering the bitumen its high quality of binder. The silica shell is responsible for the high storage stability and, when mixed with aggregates for end use of asphalt, as for example in pavement applications, serves as mineral charge to the bitumen, modifying the bitumen ow properties. Indeed, when heated at 100 \°C and crushed, the capsules break releasing thus the bitumen. This suspension made of bitumen and silica shell fragments exhibits an interesting shear-thinning behavior that can be attributed to the presence of the remnant fragments. Indeed, when shell fragments have been transferred into a silicon oil, initially exhibiting a Newtonian behavior, the mixture of fragments and oil also exhibited a shear thinning rheogram demonstrating the e ect of the silica shell fragments. The bene t of such a behavior modi cation is the possibility to reduce or avoid the usual addition of llers. Passive adhesion has been tested by generating asphalt concretes with Bitumen@SiO2 powders and showed high stability.

}, issn = {09277757}, doi = {10.1016/j.colsurfa.2019.03.048}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0927775719302420}, author = {Anaclet, Pauline and Depardieu, Martin and Laurichesse, Eric and Julien, Viviane and Hung, Yvong and Schmitt, Veronique and Backov, Renal} } @article {659, title = {Bulk Photodriven CO2 Conversion through TiO2@Si(HIPE) Monolithic Macrocellular Foams}, journal = {Advanced Functional Materials}, volume = {3}, year = {2019}, month = {Jan-07-2019}, pages = {1807767}, abstract = {

Operating photo-induced reactions exclusively on catalyst surfaces while not exploiting the full catalyst volume generates a major footprint penalty for the photocatalytic reactor and leads to an inefficient use of the catalytic material. Photonic investigations clearly show that the solid foams have a strongly multidiffusive character, with photons being significantly trapped within the sample cores while addressing a photon mean free path lt = 20.1 \± 1.3 \µm. This 3D process both greatly limits back-reactions and promotes outstanding selectivity toward methane (around 80\%) generation, and even ethane (around 18\%) through C-C coupling reaction, with residual carbon monoxide and dihydrogen contents (around 2\%). Silica\–titania TiO2@Si(HIPE) self-standing macrocellular catalysts lead to optimal efficient thicknesses up to 20 times those of powders, thereby enhancing the way for real 3D-photodriven catalytic processes above the millimeter scale and up to a 6 mm thickness. A rather simple Langmuir\–Hinshelwood based kinetic model is proposed which highlights the strong dependence of photocatalytic reaction rates on light scattering and the crucial role on oxidation back-reactions. In addition, a strong correlation between light attenuation coefficient and photon mean free path and median pore aperture diameter is demonstrated, offering thus a tool for photocatalytic behavior prediction.

}, doi = {10.1002/adfm.201807767}, url = {http://doi.wiley.com/10.1002/adfm.201807767}, author = {Bernadet, Sophie and Tavernier, Eug{\'e}nie and Ta, Duc-Minh and Vall{\'e}e, Renaud A. L. and Ravaine, Serge and F{\'e}cant, Antoine and Backov, Renal} } @article {665, title = {Cutting floating single-walled carbon nanotubes with a {\textquoteleft}CO2 blade{\textquoteright}}, journal = {Carbon}, volume = {143}, year = {2019}, month = {Mar-2019}, pages = {481 - 486}, abstract = {

Uniform ultra-short (\< 100 nm) single-walled carbon nanotubes (SWCNTs) with properties of rich chemistry, high dispersity and easy manipulation, are of great importance for constructing novel nanostructures and highly integrated miniature devices. Herein, we report a recent breakthrough in cutting long SWCNTs into uniform ultra-short segments in gas-phase using CO2 as a \&$\#$39;blade.\&$\#$39; SWCNTs synthesized by an aerosol reactor are directly introduced into a second reactor for gaseous cutting. The quality and the number concentration of shortened SWCNTs are enhanced after the gas-phase cutting process. Moreover, the growth and cutting of SWCNTs are accomplished in a continuous gas-phase process, thus allows direct dry deposition of ultra-short SWCNTs as individual macromolecules or thin films onto various substrates for multiple applications. (C) 2018 Elsevier Ltd. All rights reserved.

}, issn = {00086223}, doi = {10.1016/j.carbon.2018.11.035}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0008622318310558}, author = {Tian, Ying and Wei, Nan and Laiho, Patrik and Ahmad, Saeed and Yann Magnin and Liao, Yongping and Christophe Bichara and Jiang, Hua and Kauppinen, Esko I.} } @article {669, title = {Fiber plucking by molecular motors yields large emergent contractility in stiff biopolymer networks}, journal = {Soft Matter}, volume = {15}, year = {2019}, month = {Feb-21-2020}, pages = {1481 - 1487}, abstract = {

The mechanical properties of the cell depend crucially on the tension of its cytoskeleton, a biopolymer network that is put under stress by active motor proteins. While the fibrous nature of the network is known to strongly affect the transmission of these forces to the cellular scale, our understanding of this process remains incomplete. Here we investigate the transmission of forces through the network at the individual filament level, and show that active forces can be geometrically amplified as a transverse motor-generated force \"plucks\&$\#$39;\&$\#$39; the fiber and induces a nonlinear tension. In stiff and densely connected networks, this tension results in large network-wide tensile stresses that far exceed the expectation drawn from a linear elastic theory. This amplification mechanism competes with a recently characterized network-level amplification due to fiber buckling, suggesting that that fiber networks provide several distinct pathways for living systems to amplify their molecular forces.

}, issn = {1744-683X}, doi = {10.1039/C8SM00979A}, url = {http://xlink.rsc.org/?DOI=C8SM00979Ahttp://pubs.rsc.org/en/content/articlepdf/2019/SM/C8SM00979A}, author = {Ronceray, Pierre and Broedersz, Chase P. and Lenz, Martin} } @article {594, title = {Investigation of mixed ionic/nonionic building blocks for the dual templating of macro-mesoporous silica}, journal = {Journal of Colloid and Interface Science}, volume = {533}, year = {2019}, month = {Jan-01-2019}, pages = {385 - 400}, abstract = {

Traditional porous monoliths Si(HIPE) (High Internal Phase Emulsion), prepared from the Tetradecyltrimethylammonium Bromide (TTAB)/dodecane/water system, offer high specific surface area, mainly due to microporosity. Aside, mesoporous materials SBA-15, prepared from Pluronic P123, have a high specific surface area, but are obtained as powder, which limits their applications. Starting from the mixed TTAB-P123 surfactant, it is expected to tune the mesoporosity of Si(HIPE), while keeping their monolithic character.

The ternary TTAB/P123/water phase diagram was established by varying the weight ratio between these two surfactants. The micellar structure as well as the structural parameters of the liquid crystal domains were determined by SAXS (Small Angle X-ray Scattering). The effect of dodecane solubilization was also investigated and concentrated emulsions were formulated from the (P123/TTAB)/dodecane/ water systems. After this soft matter dedicated study, the acquired knowledge was transferred toward the hierarchical porous silica generations, where the sol-gel process is involved.

Mixing P123 with TTAB, macro-mesoporous monolithic silica with an enhanced contribution of the specific surface area due to mesoporosity can be prepared. The variation of the TTAB/P123 weight ratio allows controlling the porosity at the mesoscale. Moreover, the macroporosity can be tuned by changing the preparation method, by mixing either the two micellar solutions or directly the two surfactants prior the emulsification process. (C) 2018 Elsevier Inc. All rights reserved.

}, issn = {00219797}, doi = {10.1016/j.jcis.2018.08.068}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0021979718309883}, author = {Roucher, Armand and Emo, Melanie and Vibert, Francois and Stebe, Marie-Jose and Schmitt, Veronique and Jonas, Florian and Backov, Renal and Blin, Jean-Luc} } @article {666, title = {Modified Szeg{\"o}{\textendash}Widom Asymptotics for Block Toeplitz Matrices with Zero Modes}, journal = {Journal of Statistical Physics}, volume = {174}, year = {2019}, month = {Jan-2019}, pages = {28 - 39}, abstract = {

The Szego-Widom theorem provides an expression for the determinant of block Toeplitz matrices in the asymptotic limit of large matrix dimension n. We show that the presence of zero modes, i.e, eigenvalues that vanish as n, ||\<1, when n, requires a modification of the Szego-Widom theorem. A new asymptotic expression for the determinant of a certain class of block Toeplitz matrices with one pair of zero modes is derived. The result is inspired by one-dimensional topological superconductors, and the relation with the latter systems is discussed.

}, issn = {0022-4715}, doi = {10.1007/s10955-018-2177-8}, url = {http://link.springer.com/10.1007/s10955-018-2177-8}, author = {Basor, E. and Dubail, Jerome and Emig, Thorsten and Santachiara, Raoul} } @article {679, title = {Multiscale poromechanics of wet cement paste}, journal = {Proceedings of the National Academy of Sciences}, volume = {2}, year = {2019}, month = {May-09-2019}, pages = {201901160}, abstract = {

Capillary effects, such as imbibition drying cycles, impact the mechanics of granular systems over time. A multiscale poromechanics framework was applied to cement paste, which is the most common building material, experiencing broad humidity variations over the lifetime of infrastructure. First, the liquid density distribution at intermediate to high relative humidity is obtained using a lattice gas density functional method together with a realistic nanogranular model of cement hydrates. The calculated adsorption/desorption isotherms and pore size distributions are discussed and compare well with nitrogen and water experiments. The standard method for pore size distribution determination from desorption data is evaluated. Second, the integration of the Korteweg liquid stress field around each cement hydrate particle provided the capillary forces at the nanoscale. The cement mesoscale structure was relaxed under the action of the capillary forces. Local irreversible deformations of the cement nanograins assembly were identified due to liquid\–solid interactions. The spatial correlations of the nonaffine displacements extend to a few tens of nanometers. Third, the Love\–Weber method provided the homogenized liquid stress at the micrometer scale. The homogenization length coincided with the spatial correlation length of nonaffine displacements. Our results on the solid response to capillary stress field suggest that the micrometer-scale texture is not affected by mild drying, while nanoscale irreversible deformations still occur. These results pave the way for understanding capillary phenomena-induced stresses in heterogeneous porous media ranging from construction materials to hydrogels and living systems.

}, issn = {0027-8424}, doi = {10.1073/pnas.1901160116}, url = {http://www.pnas.org/lookup/doi/10.1073/pnas.1901160116}, author = {Zhou, Tingtao and Katerina Ioannidou and Franz-Josef Ulm and Bazant, Martin Z. and Roland Jean-Marc Pellenq} } @article {655, title = {Stress-dependent amplification of active forces in nonlinear elastic media}, journal = {Soft Matter}, volume = {15}, year = {2019}, month = {Jan-14-2019}, pages = {331 - 338}, abstract = {

The production of mechanical stresses in living organisms largely relies on localized, force-generating active units embedded in filamentous matrices. Numerical simulations of discrete fiber networks with fixed boundaries have shown that buckling in the matrix dramatically amplifies the resulting active stresses. Here we extend this result to a continuum elastic medium prone to buckling subjected to an arbitrary external stress, and derive analytical expressions for the active, nonlinear constitutive relations characterizing the full active medium. Inserting these relations into popular active gel descriptions of living tissues and the cytoskeleton will enable investigations into nonlinear regimes previously inaccessible due to the phenomenological nature of these theories.

}, issn = {1744-683X}, doi = {10.1039/C8SM00949J}, url = {http://xlink.rsc.org/?DOI=C8SM00949J}, author = {Ronceray, Pierre and Broedersz, Chase P. and Lenz, Martin} } @article {656, title = {Virus-templated Pt{\textendash}Ni(OH)2 nanonetworks for enhanced electrocatalytic reduction of water}, journal = {Nano Energy}, volume = {58}, year = {2019}, month = {Avr-2019}, pages = {167 - 174}, abstract = {

Clean hydrogen production via water electrolysis is incumbent upon the development of high-performing hydrogen evolution reaction electrocatalysts. Despite decades of commercial maturity, however, alkaline water electrolyzers continue to suffer from limitations in electrocatalytic activity and stability, even with noble metal catalysts. In recent years, combining platinum with oxophilic materials, such as metal hydroxides, has shown great promise for improving performance potentially by enabling stronger water dissociation at the surface of electrocatalysts. In this work, we leveraged the nanoscopic proportions and surface programmability of the filamentous M13 bacteriophage in the design, synthesis, and exceptional performance of 3D nanostructured biotemplated electrocatalysts for alkaline hydrogen evolution. We developed a facile synthesis method for phage-templated, Pt\–Ni(OH)2 nanonetworks, relying on scalable techniques like electroless deposition. After optimization of the platinum content, our materials display \–4.9 A mg\–1Pt at \−70 mV versus the reversible hydrogen electrode, the highest reported mass activity in 1 M KOH to date, and undergo minimal changes in overpotential under galvanostatic operation at \−10 mA cm\–2geo. Looking forward, the performance of these catalysts suggests that biotemplating nanostructures with M13 bacteriophage offers an interesting new route for developing high-performing electrocatalysts.

}, issn = {22112855}, doi = {10.1016/j.nanoen.2018.12.083}, url = {https://linkinghub.elsevier.com/retrieve/pii/S2211285518309960}, author = {Records, William C. and Yoon, Youngmin and Ohmura, Jacqueline F. and Chanut, Nicolas and Belcher, Angela M.} } @article {534, title = {Atomistic and mesoscale simulation of sodium and potassium adsorption in cement paste}, journal = {The Journal of Chemical Physics}, volume = {14963}, year = {2018}, month = {Aug-21-2018}, pages = {074705}, abstract = {

An atomistic and mesoscopic assessment of the effect of alkali uptake in cement paste is performed. Semi-grand canonical Monte Carlo simulations indicate that Na and K not only adsorb at the pore surface of calcium silicate hydrates (C-S-H) but also adsorb in the C-S-H hydrated interlayer up to concentrations of the order of 0.05 and 0.1 mol/kg, respectively. Sorption of alkali is favored as the Ca/Si ratio of C-S-H is reduced. Long timescale simulations using the Activation Relaxation Technique indicate that characteristic diffusion times of Na and K in the C-S-H interlayer are of the order of a few hours. At the level of individual grains, Na and K adsorption leads to a reduction of roughly 5\% of the elastic moduli and to volume expansion of about 0.25\%. Simulations using the so-called primitive model indicate that adsorption of alkali ions at the pore surface can reduce the binding between C-S-H grains by up to 6\%. Using a mesoscopic model of cement paste, the combination of individual grain swelling and changes in inter-granular cohesion was estimated to lead to overall expansive pressures of up to 4 MPa\—and typically of less than 1 MPa\—for typical alkali concentrations observed at the proximity of gel veins caused by the alkali-silica reaction.

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}, issn = {0021-9606}, doi = {10.1063/1.5042755}, url = {https://aip.scitation.org/doi/10.1063/1.5042755}, author = {Dufresne, Alice and Arayro, Jack and Zhou, Tingtao and Katerina Ioannidou and Franz-Josef Ulm and Roland Jean-Marc Pellenq and B{\'e}land, Laurent Karim} } @article {579, title = {Computing the linear viscoelastic properties of soft gels using an optimally windowed chirp protocol}, journal = {Journal of Rheology}, volume = {62}, year = {2018}, month = {Jul-2018}, pages = {1037 - 1050}, abstract = {

We use molecular dynamics simulations to investigate the linear viscoelastic response of a model three-dimensional particulate gel. The numerical simulations are combined with a novel test protocol (the optimally windowed chirp or OWCh), in which a continuous exponentially varying frequency sweep windowed by a tapered cosine function is applied. The mechanical response of the gel is then analyzed in the Fourier domain. We show that (i) OWCh leads to an accurate computation of the full frequency spectrum at a rate significantly faster than with the traditional discrete frequency sweeps, and with a reasonably high signal-to-noise ratio, and (ii) the bulk viscoelastic response of the microscopic model can be described in terms of a simple mesoscopic constitutive model. The simulated gel response is in fact well described by a mechanical model corresponding to a fractional Kelvin-Voigt model with a single Scott-Blair (or springpot) element and a spring in parallel. By varying the viscous damping and the particle mass used in the microscopic simulations over a wide range of values, we demonstrate the existence of a single master curve for the frequency dependence of the viscoelastic response of the gel that is fully predicted by the constitutive model. By developing a fast and robust protocol for evaluating the linear viscoelastic spectrum of these soft solids, we open the path toward novel multiscale insight into the rheological response for such complex materials. (C) 2018 The Society of Rheology.

}, issn = {0148-6055}, doi = {10.1122/1.5018715}, url = {http://sor.scitation.org/doi/10.1122/1.5018715}, author = {Bouzid, Mehdi and Keshavarz, Bavand and Geri, Michela and Divoux, Thibaut and Emanuela Del Gado and McKinley, Gareth H.} } @article {577, title = {Entropy-driven stability of chiral single-walled carbon nanotubes}, journal = {Science}, volume = {362}, year = {2018}, month = {Oct-12-2018}, pages = {212 - 215}, abstract = {

Single-walled carbon nanotubes are hollow cylinders that can grow centimeters long via carbon incorporation at the interface with a catalyst. They display semiconducting or metallic characteristics, depending on their helicity, which is determined during their growth. To support the quest for a selective synthesis, we develop a thermodynamic model that relates the tube-catalyst interfacial energies, temperature, and the resulting tube chirality. We show that nanotubes can grow chiral because of the configurational entropy of their nanometer-sized edge, thus explaining experimentally observed temperature evolutions of chiral distributions. Taking the chemical nature of the catalyst into account through interfacial energies, we derive structural maps and phase diagrams that will guide a rational choice of a catalyst and growth parameters toward a better selectivity.

}, issn = {0036-8075}, doi = {10.1126/science.aat6228}, url = {http://www.sciencemag.org/lookup/doi/10.1126/science.aat6228}, author = {Yann Magnin and Amara, Hakim and Ducastelle, Francois and Loiseau, Annick and Christophe Bichara} } @article {632, title = {On the existence and origin of sluggish diffusion in chemically disordered concentrated alloys}, journal = {Current Opinion in Solid State and Materials Science}, volume = {22}, year = {2018}, month = {Jun-2018}, pages = {65-74}, abstract = {

Concentrated single phase solid solutions, including medium- and high-entropy alloys, represent a new class of materials that have recently attracted significant interest due to exceptional functional and structural properties. Their fascinating properties are mainly attributed to the sluggish atomic-level diffusion and transport, but its controlling mechanisms are largely unknown and there is certain skepticism about its very existence. By using microsecond-scale molecular dynamics, on-the-fly and conventional kinetic Monte Carlo, we reveal the governing role of percolation effects and composition dependence of the vacancy migration energy in diffusion. Surprisingly, an increase of concentration of faster species (Fe) in face-centered cubic Ni-Fe alloy may decrease the overall atomic diffusion. Consequently, the composition dependence of tracer diffusion coefficient has a minimum near the site percolation threshold, similar to 20 at.\%Fe. We argue that this coupled percolation and composition-dependent barriers for vacancy jumps within different subsystems in medium- and high-entropy alloys leads, indeed, to the sluggish diffusion. A fast method for preselecting materials with potentially desired properties is suggested.

}, issn = {13590286}, doi = {10.1016/j.cossms.2018.05.003}, url = {https://linkinghub.elsevier.com/retrieve/pii/S135902861830038X}, author = {Osetsky, N. and B{\'e}land, Laurent Karim and Barashev, Alexander V. and Zhang, Yanwen} } @article {630, title = {Mesoscale structure, mechanics, and transport properties of source rocks{\textquoteright} organic pore networks}, journal = {Proceedings of the National Academy of Sciences}, volume = {115}, year = {2018}, month = {Dec-04-2018}, pages = {12365-12370}, abstract = {

Organic matter is responsible for the generation of hydrocarbons during the thermal maturation of source rock formation. This geochemical process engenders a network of organic hosted pores that governs the flow of hydrocarbons from the organic matter to fractures created during the stimulation of production wells. Therefore, it can be reasonably assumed that predictions of potentially recoverable confined hydrocarbons depend on the geometry of this pore network. Here, we analyze mesoscale structures of three organic porous networks at different thermal maturities. We use electron tomography with subnanometric resolution to characterize their morphology and topology. Our 3D reconstructions confirm the formation of nanopores and reveal increasingly tortuous and connected pore networks in the process of thermal maturation. We then turn the binarized reconstructions into lattice models including information from atomistic simulations to derive mechanical and confined fluid transport properties. Specifically, we highlight the influence of adsorbed fluids on the elastic response. The resulting elastic energy concentrations are localized at the vicinity of macropores at low maturity whereas these concentrations present more homogeneous distributions at higher thermal maturities, due to pores\&$\#$39; topology. The lattice models finally allow us to capture the effect of sorption on diffusion mechanisms with a sole input of network geometry. Eventually, we corroborate the dominant impact of diffusion occurring within the connected nanopores, which constitute the limiting factor of confined hydrocarbon transport in source rocks.

}, keywords = {porous media; electron tomography; mechanics; fluid transport; mesoscale}, issn = {0027-8424}, doi = {10.1073/pnas.1808402115}, url = {http://www.pnas.org/lookup/doi/10.1073/pnas.1808402115}, author = {Berthonneau, Jeremie and Ama{\"e}l Obliger and Valdenaire, Pierre-Louis and Grauby, Olivier and Ferry, Daniel and Chaudanson, Damien and Pierre E. Levitz and Kim, Jae Jin and Franz-Josef Ulm and Roland Jean-Marc Pellenq} } @article {627, title = {Multiscale modeling for bioresources and bioproducts}, journal = {Innovative Food Science \& Emerging Technologies}, volume = {46}, year = {2018}, month = {Avr-2018}, pages = {41 - 53}, abstract = {

Designing and processing complex matter and materials are key objectives of bioresource and bioproduct research. Modeling approaches targeting such systems have to account for their two main sources of complexity: their intrinsic multi-scale nature; and the variability and heterogeneity inherent to all living systems. Here we provide insight into methods developed at the Food \& Bioproduct Engineering division (CEPIA) of the French National Institute of Agricultural Research (INRA). This brief survey focuses on innovative research lines that tackle complexity by mobilizing different approaches with complementary objectives. On one hand cognitive approaches aim to uncover the basic mechanisms and laws underlying the emerging collective properties and macroscopic behavior of soft-matter and granular systems, using numerical and experimental methods borrowed from physics and mechanics. The corresponding case studies are dedicated to the structuring and phase behavior of biopolymers, powders and granular materials, and to the evolution of these structures caused by external constraints. On the other hand machine learning approaches can deal with process optimizations and outcome predictions by extracting useful information and correlations from huge datasets built from experiments at different length scales and in heterogeneous conditions. These predictive methods are illustrated in the context of cheese ripening, grape maturity prediction and bacterial production.

}, issn = {14668564}, doi = {10.1016/j.ifset.2017.09.015}, url = {https://linkinghub.elsevier.com/retrieve/pii/S1466856417302230}, author = {Barnabe, M. and Blanc, Nicolas and Chabin, T. and Jean-Yves Delenne and Duri, A. and Frank, Xavier and Hugouvieux, V. and Lutton, E. and Mabille, F. and Saeid Nezamabadi and Perrot, N. and Farhang Radja{\"\i} and Ruiz, T. and Tonda, A.} } @article {532, title = {Phase separation of stable colloidal clusters}, journal = {Physical Review Materials}, volume = {2}, year = {2018}, month = {Sep-25-2018}, abstract = {

This article presents a nonequilibrium thermodynamic theory for the mean-field precipitation, aggregation, and pattern formation of colloidal clusters. A variable gradient energy coefficient and the arrest of particle diffusion upon \“jamming\” of cluster aggregates in the spinodal region predicts observable gel patterns that, at high intercluster attraction, form system-spanning, out-of-equilibrium networks with glasslike, quasistatic structural relaxation. For reactive systems, we incorporate the free energy landscape of stable prenucleation clusters into the Allen-Cahn reaction equation. We show that pattern formation is dominantly controlled by the Damk\öhler number and the stability of the clusters, which modifies the autocatalytic rate of precipitation. As clusters individually become more stable, bulk phase separation is suppressed.

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}, doi = {10.1103/PhysRevMaterials.2.095602}, url = {https://journals.aps.org/prmaterials/abstract/10.1103/PhysRevMaterials.2.095602}, author = {Petersen, Thomas and Bazant, Martin Z. and Roland Jean-Marc Pellenq and Franz-Josef Ulm} } @article {660, title = {Sol{\textendash}gel process and complex fluids: sculpting porous matter at various lengths scales towards the Si(HIPE), Si(PHIPE), and SBA-15-Si(HIPE) series}, journal = {Journal of Sol-Gel Science and Technology}, volume = {18}, year = {2018}, month = {Sep-11-2018}, abstract = {

Taking inspiration from diatom hierarchically organized porosity, synthetic porous monoliths have been synthesized through rational designs while combining sol\–gel chemistry, emulsions, Pickering-based emulsions, and lyotropic mesophases. We have described the synthesis of the Si(HIPE) series employing traditional emulsions to tune the macroscopic void diameters and cationic surfactant molecules to both stabilize the oil/water interface at the macroscopic length scale and create vermicular poorly organized porosity at the mesoscopic length scale. In a second part, while substituting surfactant molecules with modified silica nanoparticles acting as emulsion-stabilizers, we depict the possibility of tuning independently the macroscopic cell diameters and the cell junctions via Pickering emulsions employed as templates, leading to the Si(PHIPE) series presenting both monodiperse macroscopic void and cell junction diameters. Finally taking the synergetic effect of nonionic surfactants and a kosmotrope salt effect we show that it is possible generating self-standing Si(HIPE) bearing high organized mesoporosity while addressing the SBA-15-Si(HIPE) series. Open image in new window Taking inspiration from diatom hierarchically organized porosity, synthetic porous self-standing silica foams have been obtained through rational designs where sol\–gel chemistry, emulsions, Pickering-based emulsions and lyotropic mesophases are advantageously combined.

}, issn = {0928-0707}, doi = {10.1007/s10971-018-4794-8}, url = {http://link.springer.com/10.1007/s10971-018-4794-8}, author = {Roucher, Armand and Schmitt, Veronique and Blin, Jean-Luc and Backov, Renal} } @article {652, title = {Synthesis, characterization, and catalytic application in aldehyde hydrosilylation of half-sandwich nickel complexes bearing (κ1-C)- and hemilabile (κ 2-C, S)-thioether-functionalised NHC ligands}, journal = {Dalton Transactions}, volume = {47}, year = {2018}, month = {Dec-21-2018}, pages = {17134-17145}, abstract = {

Neutral nickel-N-heterocyclic carbene complexes, ((1)-C)-[NiCpBr{R-NHC-(CH2)(2)SR}] [Cp = (5)-C5H5; R-NHC-(CH2)(2)SR = 1-mesityl-3-[2-(tert-butylthio)ethyl]- (1a), 1-mesityl-3-[2-(phenylthio)ethyl]- (1b), 1-benzyl-3-[2-(tert-butylthio)ethyl]- (1c), 1-benzyl-3-[2-(phenylthio)ethyl]-imidazol-2-ylidene (1d)], which bear a N-bound thioether side arm, were prepared by the reaction of nickelocene with the corresponding imidazolium bromides [R-NHC-(CH2)(2)SRHBr] (a-d), via conventional or microwave heating. The H-1 NMR spectra of the benzyl-substituted species 1c and 1d showed signals for diastereotopic NCH2CH2S protons at room temperature. However, structural studies established the absence of coordination of the sulphur atom in the solid state, and solvent DFT calculations showed that bromide displacement by sulphur is an unfavourable process (G = +13.5 kcal mol(-1) for 1d), thereby suggesting that the observed disatereotopicity is more likely due to significant steric congestion rather than to a possible C,S-chelation in solution. Treatment of these complexes with KPF6 in tetrahydrofuran (THF) led to bromide abstraction to afford the cationic complexes [NiCp{R-NHC-(CH2)(2)SR}](PF6) (2a-c). Alternatively, 2a-c could also be prepared by the direct reaction of nickelocene with the corresponding imidazolium hexafluorophosphate salts [R-NHC-(CH2)(2)SRHPF6]. Inversely to the neutral species, whereas X-ray crystallography established C,S-chelation in the solid state, the H-1 NMR spectra (CDCl3, CD2Cl2, or thf-d(8)) at room temperature showed no diastereotopic NCH2CH2S protons, thus suggesting the possible displacement of the sulphur atom by the respective solvents and/or very fast sulphur inversion. DFT calculations established a low energy inversion process in all cases (+9 G(double dagger) +13 kcal mol(-1)) as well as a favourable solvent coordination process (G(double dagger) approximate to +11 kcal mol(-1); G approximate to -7 kcal mol(-1)) with a solvent such as THF, thus suggesting that sulphur inversion and/or solvent coordination can both account for the absence of diastereotopy at room temperature, depending on the solvent. While all complexes catalysed the hydrosilylation of benzaldehyde in the absence of any additive, the cationic C,S-chelated complexes 2 proved more active than the sterically constrained neutral species 1. In particular, 2c proved to be the most active pre-catalyst and its catalytic charge could be lowered down to 2 mol\% with PhSiH3 as the hydrogen source.

}, issn = {1477-9226}, doi = {10.1039/C8DT03882A}, url = {http://xlink.rsc.org/?DOI=C8DT03882A}, author = {Franz-Josef Ulm and Poblador-Bahamonde, Amalia I. and Choppin, Sabine and Bellemin-Laponnaz, St{\'e}phane and Chetcuti, Michael J. and Achard, Thierry and Ritleng, Vincent} } @article {573, title = {Thermodynamics, kinetics, and mechanics of cesium sorption in cement paste: A multiscale assessment}, journal = {Physical Review Materials}, volume = {2}, year = {2018}, month = {May-30-2018}, chapter = {Article Number: 053608 }, abstract = {

Cesium-137 is a common radioactive byproduct found in nuclear spent fuel. Given its 30 year half life, its interactions with potential storage materials-such as cement paste-is of crucial importance. In this paper, simulations are used to establish the interaction of calcium silicate hydrates (C-S-H)-the mam binding phase of cement paste-with Cs at the nano- and mesoscale. Different C-S-H compositions are explored, including a range of Ca/Si ratios from 1.0 to 2.0. These calculations are based on a set of 150 atomistic models, which qualitatively and quantitatively reproduce a number of experimentally measured features of C-S-H-within limits intrinsic to the approximations imposed by classical molecular dynamics and the steps followed when building the models. A procedure where hydrated Ca2+ ions are swapped for Cs1+ ions shows that Cs adsorption in the C-S-H interlayer is preferred to Cs adsorption at the nanopore surface when Cs concentrations are lower than 0.19 Mol/kg. Interlayer sorption decreases as the Ca/Si ratio increases. The activation relaxation technique nouveau is used to access timescales out of the reach of traditional molecular dynamics (MD). It indicates that characteristic diffusion time for Cs1+ in the C-S-H interlayer is on the order of a few hours. Cs uptake in the interlayer has little impact on the elastic response of C-S-H. It leads to swelling of the C-S-H grams, but mesoscale calculations that access length scales out of the range of MD indicate that this leads to practically negligible expansive pressures for Cs concentrations relevant to nuclear waste repositories.

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}, keywords = {CALCIUM-SILICATE-HYDRATE; C-S-H; MOLECULAR-DYNAMICS; CRYSTAL-STRUCTURE; MONTE-CARLO; IMMOBILIZATION; RADIONUCLIDES; SIMULATIONS; RELAXATION; COLLOIDS}, doi = {10.1103/PhysRevMaterials.2.053608}, url = {https://link.aps.org/doi/10.1103/PhysRevMaterials.2.053608}, author = {Arayro, Jack and Dufresne, Alice and Zhou, Tingtao and Katerina Ioannidou and Franz-Josef Ulm and Roland Jean-Marc Pellenq and B{\'e}land, Laurent Karim} } @article {633, title = {Two-dimensional numerical simulation of chimney fluidization in a granular medium using a combination of discrete element and lattice Boltzmann methods}, journal = {Physical Review E}, volume = {97}, year = {2018}, month = {May-10-2018}, pages = { Article Number 052902 }, abstract = {

We present here a numerical study dedicated to the fluidization of a submerged granular medium induced by a localized fluid injection. To this end, a two-dimensional (2D) model is used, coupling the lattice Boltzmann method (LBM) with the discrete element method (DEM) for a relevant description of fluid-grains interaction. An extensive investigation has been carried out to analyze the respective influences of the different parameters of our configuration, both geometrical (bed height, grain diameter, injection width) and physical (fluid viscosity, buoyancy). Compared to previous experimental works, the same qualitative features are recovered as regards the general phenomenology including transitory phase, stationary states, and hysteretic behavior. We also present quantitative findings about transient fluidization, for which several dimensionless quantities and scaling laws are proposed, and about the influence of the injection width, from localized to homogeneous fluidization. Finally, the impact of the present 2D geometry is discussed, by comparison to the real three-dimensional (3D) experiments, as well as the crucial role of the prevailing hydrodynamic regime within the expanding cavity, quantified through a cavity Reynolds number, that can presumably explain some substantial differences observed regarding upward expansion process of the fluidized zone when the fluid viscosity is changed.

}, issn = {2470-0045}, doi = {10.1103/PhysRevE.97.052902}, url = {https://link.aps.org/doi/10.1103/PhysRevE.97.052902}, author = {Jeff Ngoma and Pierre Philippe and St{\'e}phane Bonelli and Farhang Radja{\"\i} and Jean-Yves Delenne} } @article {624, title = {Accurate classical short-range forces for the study of collision cascades in Fe{\textendash}Ni{\textendash}Cr}, journal = {Computer Physics Communications}, volume = {219}, year = {2017}, month = {Oct-2017}, pages = {11 - 19}, abstract = {

The predictive power of a classical molecular dynamics simulation is largely determined by the physical validity of its underlying empirical potential. In the case of high-energy collision cascades, it was recently shown that correctly modeling interactions at short distances is necessary to accurately predict primary damage production. An ab initio based framework is introduced for modifying an existing embedded-atom method FeNiCr potential to handle these short-range interactions. Density functional theory is used to calculate the energetics of two atoms approaching each other, embedded in the alloy, and to calculate the equation of state of the alloy as it is compressed. The pairwise terms and the embedding terms of the potential are modified in accordance with the ab initio results. Using this reparametrized potential, collision cascades are performed in Ni50Fe50, Ni80Cr20 and Ni33Fe33Cr33. The simulations reveal that alloying Ni and NiCr to Fe reduces primary damage production, in agreement with some previous calculations. Alloying Ni and NiFe to Cr does not reduce primary damage production, in contradiction with previous calculations.

}, issn = {00104655}, doi = {10.1016/j.cpc.2017.05.001}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0010465517301315}, author = {B{\'e}land, Laurent Karim and Tamm, Artur and Mu, Sai and Samolyuk, D. and Osetsky, N. and Aabloo, Alvo and Klintenberg, Mattias and Caro, Alfredo and Stoller, E.} } @article {600, title = {Cohesive strength of iron ore granules}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 08020}, abstract = {

We present an experimental and numerical investigation of the mechanical strength of crude iron ore (Hematite) granules in which capillary bonds between primary particles are the source of internal cohesion. The strength is measured by subjecting the granules to vertical compression between two plates. We show that the behavior of the granules is ductile with a well-defined plastic threshold which increases with the amount of water. It is found that the compressive strength scales with capillary cohesion with a pre-factor that is nearly independent of size polydispersity for the investigated range of parameters but increases with friction coefficient between primary particles. This weak dependence may be attributed to the class of fine particles which, due to their large number, behaves as a cohesive matrix that controls the strength of the granule.

}, doi = {10.1051/epjconf/201714008020}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714008020}, author = {Contreras, Rafael Jaimes and Berger, Nicolas and Izard, Edouard and Douce, Jean-Fran{\c c}ois and Koltsov, Alexey and Jean-Yves Delenne and Emilien Az{\'e}ma and Saeid Nezamabadi and van Loo, Fr{\'e}d{\'e}ric and Roland Jean-Marc Pellenq and Farhang Radja{\"\i}}, editor = {Luding, S.} } @article {244, title = {Crystal-chemistry control of the mechanical properties of 2:1 clay minerals}, journal = {Applied Clay Science}, volume = {143}, year = {2017}, month = {Jul-2017}, pages = {387 - 398}, abstract = {

Clay minerals are the main constituents of the clay matrix of a wide variety of sedimentary deposits. When subjected to burial, some of these minerals undergo phase transitions accompanied by atomic substitutions which ultimately impact the cohesive interactions between their constitutive layers. The most common among such transitions is smectite illitization, which is also highly relevant for oil and gas exploration and production from source rocks. The impact of this transition on the mechanical properties of clay minerals as well as clay bearing rocks remains, however, to be properly addressed. To this end, a set of macroscopic single 2:1 clay minerals (pyrophyllite, talc, vermiculite, phlogopite, muscovite, and clintonite) representative of the two octahedral fillings and the variation in surface charge densities was investigated. A hybrid experimental-modeling approach is proposed, which combines nanoindentation in orthogonal directions (x1 and x3-directions) with analytical derivations of the cohesive energy (Ui) using XRD and TEM-EDS measurements. The results highlight that the interlayer energy defines the elasticity (modulus M), strength (hardness H) and ductility behavior (M/H) of these materials; and not the bond energy stored into the constituent layers. This finding permits the derivation of predictive stiffness and strength functional relations as derivatives of the interlayer energy that account for the arrangement of nanoscale layers and the interlayer composition. These relations suggest that as the cohesion increases with the coulombic interactions through progressive smectite illitization, the system loses its capacity to dissipate applied energy by dislocation mechanisms in between the layers, entailing an increase in brittleness of the clay particles with burial. By way of conclusion, the geophysics and geochemistry implications of these results for predicting the macroscopic mechanical performance of clay bearing geomaterials, such as economically valuable source rocks, are discussed.

}, issn = {01691317}, doi = {10.1016/j.clay.2017.04.010}, author = {Berthonneau, Jeremie and Christian G. Hoover and Grauby, Olivier and Alain Baronnet and Roland Jean-Marc Pellenq and Franz-Josef Ulm} } @article {588, title = {From cellulose to kerogen: molecular simulation of a geological process}, journal = {Chemical Science}, volume = {8}, year = {2017}, month = {Dec-01-2017}, pages = {8325-8335}, abstract = {

The process by which organic matter decomposes deep underground to form petroleum and its underlying kerogen matrix has so far remained a no man\&$\#$39;s land to theoreticians, largely because of the geological (Myears) timescale associated with the process. Using reactive molecular dynamics and an accelerated simulation framework, the replica exchange molecular dynamics method, we simulate the full transformation of cellulose into kerogen and its associated fluid phase under prevailing geological conditions. We observe in sequence the fragmentation of the cellulose crystal and production of water, the development of an unsaturated aliphatic macromolecular phase and its aromatization. The composition of the solid residue along the maturation pathway strictly follows what is observed for natural type III kerogen and for artificially matured samples under confined conditions. After expulsion of the fluid phase, the obtained microporous kerogen possesses the structure, texture, density, porosity and stiffness observed for mature type III kerogen and a microporous carbon obtained by saccharose pyrolysis at low temperature. As expected for this variety of precursor, the main resulting hydrocarbon is methane. The present work thus demonstrates that molecular simulations can now be used to assess, almost quantitatively, such complex chemical processes as petrogenesis in fossil reservoirs and, more generally, the possible conversion of any natural product into bio-sourced materials and/or fuel.

}, issn = {2041-6520}, doi = {10.1039/C7SC03466K}, url = {http://xlink.rsc.org/?DOI=C7SC03466K}, author = {Atmani, Lea and Christophe Bichara and Roland Jean-Marc Pellenq and Henri Van Damme and Adri CT Van Duin and Raza, Zamaan and Truflandier, Lionel A. and Ama{\"e}l Obliger and Kralert, Paul G. and Franz-Josef Ulm and Jean-Marc Leyssale} } @article {595, title = {Heat-induced aging of agar solutions: Impact on the structural and mechanical properties of agar gels}, journal = {Food Hydrocolloids}, volume = {64}, year = {2017}, month = {Mar-2017}, pages = {59 - 69}, abstract = {

Thermoreversible gels are commonly prepared by cooling down to ambient temperature, aqueous polymer solutions first brought to a boil for a short time. Here, we study the effect of the latter duration on the subsequent gelation of an agar solution. Increasing the incubation time at high temperature (T= 80 degrees C) from hours to a few days leads to the hydrolysis and the oxidation of the polysaccharides, and results in the decrease of the viscosity and the pH of the solution. Samples withdrew at different incubation times are cooled down to form gels whose structure and mechanical properties are systematically determined. Cryoelectron microscopy and X-ray diffraction experiments reveal that agar gels formed from solutions of increasing incubation times, display a coarser microstructure composed of micron-sized foils which result from the condensation of the polysaccharides, and contrast with the fibrous-like microstructure of gels prepared from a fresh agar solution. Along with structural changes, a prolonged incubation time of the agar solution at T = 80 degrees C leads to weaker gels than those made from fresher solutions, and extensive macro-indentation experiments coupled to direct visualization show that the gel rupture scenario turns from brittle to ductile-like as the incubation time increases. Our study suggests that the incubation time of agar solutions at high temperature could be used as an external control parameter to tune the mechanical properties of agar-based gels. (C) 2016 Elsevier Ltd. All rights reserved.

}, keywords = {Agar; Aging; Gelation; Debonding; Indentation; Fracture}, issn = {0268005X}, doi = {10.1016/j.foodhyd.2016.10.020}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0268005X16305793}, author = {Mao, Bosi and Bentaleb, Ahmed and Louerat, Fr{\'e}d{\'e}ric and Divoux, Thibaut and Snabre, Patrick} } @article {613, title = {Inorganic, Hybridized and Living Macrocellular Foams: {\textquotedblleft}Out of the Box{\textquotedblright} Heterogeneous Catalysis}, journal = {The Chemical Record}, volume = {18}, year = {2017}, month = {Dec-01-2017}, pages = {776-787}, abstract = {

With this personal account we show how the Integrative Chemistry, when combining the sol-gel process and concentrated emulsions, allows to trigger inorganic, hybrid or living materials when dedicated toward heterogeneous catalysis applications. In here we focus on 3D-macrocellular monolithic foams bearing hierarchical porosities and applications thereof toward heterogeneous catalysis where both activities and mass transport are enhanced. We thereby first depict the general background of emulsions, focusing on concentrated ones, acting as soft templates for the design of solid (HIPE) foams, HIPE being the acronym for High Internal Phase Emulsions while encompassing both sol-gel and polymer chemistry. Secondly we extend this approach toward the design of inorganic cellular materials labeled Si(HIPE) and hybrid organic-inorganic foams, labeled Organo-Si(HIPE), where heterogeneous catalysis applications are addressed considering acidic, metallic, enzymatic and bacterial-based modified Si-HIPE. Along, we will show how the fluid hydrodynamic within the macrocellular foams is offering advanced \"out of the box\" heterogeneous catalytic capabilities.

}, keywords = {catalysts; emulsion-templating; integrative chemistry; porous matter; sol-gel process}, doi = {10.1002/tcr.v18.7-810.1002/tcr.201700075}, url = {http://doi.wiley.com/10.1002/tcr.v18.7-8}, author = {Roucher, Armand and Depardieu, Martin and Pekin, Deniz and Morvan, Micka{\"e}l and Backov, Renal} } @article {410, title = {Magnetism as indirect tool for carbon content assessment in nickel nanoparticles}, journal = {Journal of Applied Physics}, volume = {122}, year = {2017}, month = {Jul-12-2017}, pages = {213902}, abstract = {

We report a combined experimental and theoretical study to ascertain carbon solubility in nickel nanoparticles embedded into a carbon matrix via the one-pot method. This original approach is based on the experimental characterization of the magnetic properties of Ni at room temperature and Monte Carlo simulations used to calculate the magnetization as a function of C content in Ni nanoparticles. Other commonly used experimental methods fail to accurately determine the chemical analysis of these types of nanoparticles. Thus, we could assess the C content within Ni nanoparticles and it decreases from 8 to around 4\ at. \% with increasing temperature during the synthesis. This behavior could be related to the catalytic transformation of dissolved C in the Ni particles into graphite layers surrounding the particles at high temperature. The proposed approach is original and easy to implement experimentally since only magnetization measurements at room temperature are needed. Moreover, it can be extended to other types of magnetic nanoparticles dissolving carbon.

}, issn = {0021-8979}, doi = {10.1063/1.5006138}, url = {http://aip.scitation.org/doi/10.1063/1.5006138http://aip.scitation.org/doi/pdf/10.1063/1.5006138}, author = {Oumellal, Y. and Yann Magnin and {\'\i}nez de Yuso, A. and Aguiar Hualde, J. M. and Amara, H. and Paul-Boncour, V. and Matei Ghimbeu, C. and Malouche, A. and Christophe Bichara and Roland Jean-Marc Pellenq and Zlotea, C.} } @article {616, title = {Mechanisms of jamming in the Nagel-Schreckenberg model for traffic flow}, journal = {Physical Review E}, volume = {95}, year = {2017}, month = {Jan-2017}, abstract = {

We study the Nagel-Schreckenberg cellular automata model for traffic flow by both simulations and analytical techniques. To better understand the nature of the jamming transition, we analyze the fraction of stopped cars P(v=0) as a function of the mean car density. We present a simple argument that yields an estimate for the free density where jamming occurs, and show satisfying agreement with simulation results. We demonstrate that the fraction of jammed cars P(v\∈{0,1}) can be decomposed into the three factors (jamming rate, jam lifetime, and jam size) for which we derive, from random walk arguments, exponents that control their scaling close to the critical density.

}, issn = {2470-0045}, doi = {10.1103/PhysRevE.95.012311}, url = {https://link.aps.org/doi/10.1103/PhysRevE.95.012311}, author = {Bette, Henrik M. and Habel, Lars and Emig, Thorsten and Schreckenberg, Michael} } @article {587, title = {Methodology for Estimation of Nanoscale Hardness via Atomistic Simulations}, journal = {Journal of Nanomechanics and Micromechanics}, volume = {7}, year = {2017}, month = {Dec-2017}, pages = { Article Number: UNSP 04017011 }, abstract = {

Statistical mechanics has provided powerful techniques to measure mechanical properties of materials at the nanoscale and paved the way for bottom-up computational materials design. The introduction of such techniques in civil engineering applications, namely construction and geotechnical materials, remains limited to the elastic and fracture properties. This paper presents an atomistic approach to calculate the nanoscale cohesion, friction angle, and hardness. This method is based on the application of biaxial external deformation, or stress, in the weakest crystallographic direction in the material. The onset of the failure is characterized by investigating the unloading paths from several points on the stress-strain curve. Such calculations of the failure stress along different deformation paths provide multiple failure Mohr circles in the normal-shear stress space, which is found to provide a failure envelope akin to the Mohr-Coulomb failure criterion that is widely used for the plastic analysis of granular geomaterials. The failure envelope characterizes the nanoscale cohesion and friction angle, which in conjunction with continuum mechanics can be utilized to estimate the nanoscale hardness of layered materials. Application of this method to tobermorite and Na-montmorillonite crystals yields values that are close to the experimental measurements obtained using nanoindentation and atomic force microscopy techniques. (C) 2017 American Society of Civil Engineers.

}, keywords = {Atomistic simulation; Friction; Cohesion; Hardness; Tobermorite; Montmorillonite}, issn = {2153-5434}, doi = {10.1061/(ASCE)NM.2153-5477.0000127}, url = {http://ascelibrary.org/doi/10.1061/\%28ASCE\%29NM.2153-5477.0000127}, author = {Qomi, M. J. Abdolhosseini and Ebrahimi, Davoud and Mathieu Bauchy and Roland Jean-Marc Pellenq and Franz-Josef Ulm} } @article {617, title = {Nonequilibrium Fluctuational Quantum Electrodynamics: Heat Radiation, Heat Transfer, and Force}, journal = {Annual Review of Condensed Matter Physics}, volume = {8}, year = {2017}, month = {Jan-11-2017}, pages = {119 - 143}, abstract = {

Quantum-thermal fluctuations of electromagnetic waves are the cornerstone of quantum statistics and inherent to phenomena such as thermal radiation and van der Waals forces. Although the principles are found in elementary texts, recent experimental and technological advances make it necessary to come to terms with counterintuitive consequences at short scales\—the so-called near-field regime. We focus on three manifestations: (a) The Stefan\–Boltzmann law describes radiation from macroscopic bodies but fails for small objects. (b) The heat transfer between two bodies at close proximity is dominated by evanescent waves and can be orders of magnitude larger than the classical (propagating) contribution. (c) Casimir forces, dominant at submicron separation, are not sufficiently explored for objects at different temperatures (at least experimentally). We explore these phenomena using fluctuational quantum electrodynamics (QED), introduced by Rytov in the 1950s, combined with scattering formalisms. This enables investigation of different material properties, shapes, separations, and arrangements.

}, issn = {1947-5454}, doi = {10.1146/annurev-conmatphys-031016-025203}, url = {http://www.annualreviews.org/doi/10.1146/annurev-conmatphys-031016-025203}, author = {Bimonte, Giuseppe and Emig, Thorsten and Kardar, Mehran and Kr{\"u}ger, Matthias} } @article {604, title = {Numerical insight into the micromechanics of jet erosion of a cohesive granular material}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 15017}, abstract = {

Here we investigate the physical mechanisms behind the surface erosion of a cohesive granular soil induced by an impinging jet by means of numerical simulations coupling fluid and grains at the microscale. The 2D numerical model combines the Discrete Element and Lattice Boltzmann methods (DEM-LBM) and accounts for the granular cohesion with a contact model featuring a paraboloidal yield surface. Here we review first the hydrodynamical conditions imposed by the fluid jet on a solid granular packing, turning then the attention to the impact of cohesion on the erosion kinetics. Finally, the use of an additional subcritical debonding damage model based on the work of Silvani and co-workers provides a novel insight into the internal solicitation of the cohesive granular sample by the impinging jet.

}, doi = {10.1051/epjconf/201714015017}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714015017}, author = {Cuellar, Pablo and Benseghier, Zeyd and Luu, Li-Hua and St{\'e}phane Bonelli and Jean-Yves Delenne and Farhang Radja{\"\i} and Pierre Philippe}, editor = {Saeid Nezamabadi and Luding, S.} } @article {597, title = {Peridynamics simulation of the comminution of particles containing microcraks}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 07018}, abstract = {

In this study, we rely on a \’bond-based\’ peridynamic approach to investigate the strength and failure of 2D particles containing a collection of 1D microcracks. The mechanical tests were performed on disks under diametral compression. In an extensive parametric study, the distribution of microcracks was varied for different particle sizes. The evolution of yield stress with diameter and the probability of failure in terms of Weibull distributions are investigated in detail. Finally, by means of a floodfill algorithm, we analyze the variation of the mean fragment size as a function of the density of defects.

}, doi = {10.1051/epjconf/201714007018}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714007018}, author = {Blanc, Nicolas and Frank, Xavier and Mayer-Laigle, Claire and Farhang Radja{\"\i} and Jean-Yves Delenne}, editor = {Saeid Nezamabadi and Luding, S. and Jean-Yves Delenne} } @article {590, title = {Production of H 2 by water radiolysis in cement paste under electron irradiation: A joint experimental and theoretical study}, journal = {Cement and Concrete Research}, volume = {100}, year = {2017}, month = {Oct-2017}, pages = {110 - 118}, abstract = {

Long-term confinement of nuclear waste is one of the main challenges faced by the nuclear industry. Fission products such as Sr-90 and Cs-137, both beta(-) emitters known to induce serious health hazards, represent the largest fraction of nuclear waste. Cement is a good candidate to store them, provided it can resist the effects of irradiation over time. Here, we have investigated the effects of beta(-) decay on cement by performing electron irradiation experiments on different samples. We show that H-2 production in cement, the main effect of water radiolysis, depends strongly on composition and relative humidity. First-principles calculations indicate that the water-rich interlayer regions with Ca2+ ions act as electron traps that promote the formation of H-2. They also show that holes localize in water-rich regions in low Ca content samples and are then able to participate in H-2 production. This work provides new understanding of radiolysis effects in cements.

}, issn = {00088846}, doi = {10.1016/j.cemconres.2017.05.022}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0008884617302065}, author = {Le Caer, Sophie and Dezerald, Lucile and Boukari, Khaoula and Laine, Maxime and Taupin, s{\'e}bastien and Kavanagh, Ryan M. and Johnston, Conrad S.N. and Foy, Eddy and Charpentier, Thibault and Konrad J. Krakowiak and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Tribello, Gareth A. and Kohanoff, Jorge J. and Andres Sa{\`u}l} } @article {589, title = {Role of Interfaces in Elasticity and Failure of Clay{\textendash}Organic Nanocomposites: Toughening upon Interface Weakening?}, journal = {Langmuir}, volume = {33}, year = {2017}, month = {Oct-24-2017}, pages = {11457 - 11466}, abstract = {

Synthetic organic-inorganic composites constitute a new class of engineering materials finding applications in an increasing range of fields. The interface between the constituting phases plays a pivotal role in the enhancement of mechanical properties. In exfoliated clay-organic nanocomposites, individual, high aspect ratio clay sheets are dispersed in the organic matrix providing large interfaces and hence efficient stress transfer. In this study, we aim at elucidating molecular-scale reinforcing mechanisms in a series of model clay-organic composite systems by means of reactive molecular simulations. In our models, two possible locations of failure initiation are present: one is the interlayer space of the clay platelet, and the other one is the clay-organic interface. We systematically modify the cohesiveness of the interface and assess how the failure mechanism changes when the different model composites are subjected to a tensile test. Besides a change in the failure mechanism, an increase in the released energy at the interface (meaning an increased overall toughness) are observed upon weakening the interface by bond removal. We propose a theoretical analysis of these results by considering a cohesive law that captures the effect of the interface on the composite mechanics. We suggest an atomistic interpretation of this cohesive law, in particular, how it relates to the degree of bonding at the interface. In a broader perspective, this work sheds light on the importance of the orthogonal behavior of interfaces to nanocomposites.

https://pubs-acs-org.libproxy.mit.edu/appl/literatum/publisher/achs/journals/content/langd5/2017/langd5.2017.33.issue-42/acs.langmuir.7b01071/20171025/images/medium/la-2017-01071k_0008.gif

}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.7b01071}, url = {http://pubs.acs.org/doi/10.1021/acs.langmuir.7b01071}, author = {Gy{\"o}rgy Hantal and Brochard, Laurent and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Benoit A. Coasne} } @article {605, title = {Small solar system bodies as granular systems}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 14011}, abstract = {

Asteroids and other Small Solar System Bodies (SSSBs) are currently of great scientific and even industrial interest. Asteroids exist as the permanent record of the formation of the Solar System and therefore hold many clues to its understanding as a whole, as well as insights into the formation of planetary bodies. Additionally, SSSBs are being investigated in the context of impact risks for the Earth, space situational awareness and their possible industrial exploitation (asteroid mining). In all these aspects, the knowledge of the geophysical characteristics of SSSB surface and internal structure are of great importance. Given their size, constitution, and the evidence that many SSSBs are not simple monoliths, these bodies should be studied and modelled as self-gravitating granular systems in general, or as granular systems in micro-gravity environments in particular contexts. As such, the study of the geophysical characteristics of SSSBs is a multi-disciplinary effort that lies at the crossroads between Granular Mechanics, Celestial Mechanics, Soil Mechanics, Aerospace Engineering and Computer Sciences.

}, doi = {10.1051/epjconf/201714014011}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714014011}, author = {Hestroffer, Daniel and Adriano Campo Bagat{\'\i}n and Losert, Wolfgang and Opsomer, Eric and S{\'a}nchez, Paul and Scheeres, Daniel J. and Staron, Lydie and Taberlet, Nicolas and Yano, Hajime and Eggl, Siegfried and Lecomte, Charles-Edouard and Murdoch, Naomi and Farhang Radja{\"\i} and Richardson, Derek C. and Salazar, Marcos and Schwartz, Stephen R. and Tanga, Paolo}, editor = {Saeid Nezamabadi and Luding, S. and Jean-Yves Delenne} } @article {609, title = {A time-dependent atomistic reconstruction of severe irradiation damage and associated property changes in nuclear graphite}, journal = {Carbon}, volume = {120}, year = {2017}, month = {Aug-2017}, pages = {111 - 120}, abstract = {

Wheat grains can be considered as a natural cemented granular material. They are milled under high forces to produce food products such as flour. The major part of the grain is the so-called starchy endosperm. It contains stiff starch granules, which show a multi-modal size distribution, and a softer protein matrix that surrounds the granules. Experimental milling studies and numerical simulations are going hand in hand to better understand the fragmentation behavior of this biological material and to improve milling performance. We present a numerical study of the effect of granule size distribution on the strength of such a cemented granular material. Samples of bi-modal starch granule size distribution were created and submitted to uniaxial tension, using a peridynamics method. We show that, when compared to the effects of starch-protein interface adhesion and voids, the granule size distribution has a limited effect on the samples\’ yield stress.

}, keywords = {TRANSMISSION ELECTRON-MICROSCOPY; MOLECULAR-DYNAMICS SIMULATIONS; HIGHLY ANISOTROPIC PYROCARBONS; THERMAL-CONDUCTIVITY; NEUTRON-IRRADIATION; CARBON; GRAPHENE; DEFECTS; ENERGY; NANOSTRUCTURE}, issn = {00086223}, doi = {10.1016/j.carbon.2017.05.009}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0008622317304542}, author = {Baptiste Farbos and Freeman, Helen and Hardcastle, Trevor and Da Costa, Jean-Pierre and Brydson, Rik and Scott, Andrew J. and Weisbecker, Patrick and Germain Christian and G{\'e}rard L. Vignoles and Jean-Marc Leyssale} } @article {243, title = {Topological Control on the Structural Relaxation of Atomic Networks under Stress}, journal = {Physical Review Letters}, volume = {119}, year = {2017}, month = {Jul-21-2017}, pages = {Article Number: 035502}, abstract = {

Upon loading, atomic networks can feature delayed irreversible relaxation. However, the effect of composition and structure on relaxation remains poorly understood. Herein, relying on accelerated molecular dynamics simulations and topological constraint theory, we investigate the relationship between atomic topology and stress-induced structural relaxation, by taking the example of creep deformations in calcium silicate hydrates (C-S-H), the binding phase of concrete. Under constant shear stress, C-S-H is found to feature delayed logarithmic shear deformations. We demonstrate that the propensity for relaxation is minimum for isostatic atomic networks, which are characterized by the simultaneous absence of floppy internal modes of relaxation and eigenstress. This suggests that topological nanoengineering could lead to the discovery of nonaging materials.

Figure

Figure

Figure

}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.119.035502}, author = {Mathieu Bauchy and Wang, Mengyi and Yu, Yingtian and Wang, Bu and Krishnan, M. Anoop and Enrico Masoero and Franz-Josef Ulm and Roland Jean-Marc Pellenq} } @article {581, title = {Yield stress materials in soft condensed matter}, journal = {Reviews of Modern Physics}, volume = {89}, year = {2017}, month = {Aug-21-2017}, pages = { Article Number: 035005 }, abstract = {

A comprehensive review is presented of the physical behavior of yield stress materials in soft condensed matter, which encompasses a broad range of materials from colloidal assemblies and gels to emulsions and non-Brownian suspensions. All these disordered materials display a nonlinear flow behavior in response to external mechanical forces due to the existence of a finite force threshold for flow to occur: the yield stress. Both the physical origin and rheological consequences associated with this nonlinear behavior are discussed and an overview is given of experimental techniques available to measure the yield stress. Recent progress is discussed concerning a microscopic theoretical description of the flow dynamics of yield stress materials, emphasizing, in particular, the role played by relaxation time scales, the interplay between shear flow and aging behavior, the existence of inhomogeneous shear flows and shear bands, wall slip, and nonlocal effects in confined geometries.

}, issn = {0034-6861}, doi = {10.1103/RevModPhys.89.035005}, url = {https://link.aps.org/doi/10.1103/RevModPhys.89.035005}, author = {Bonn, Daniel and Denn, Morton M. and Berthier, Ludovic and Divoux, Thibaut and Manneville, S{\'e}bastien} } @article {639, title = {Activated desorption at heterogeneous interfaces and long-time kinetics of hydrocarbon recovery from nanoporous media}, journal = {Nature Communications}, volume = {7}, year = {2016}, month = {Jun-2016}, pages = { Article Number 11890 }, abstract = {

Hydrocarbon recovery from unconventional reservoirs (shale gas) is debated due to its environmental impact and uncertainties on its predictability. But a lack of scientific knowledge impedes the proposal of reliable alternatives. The requirement of hydrofracking, fast recovery decay and ultra-low permeability-inherent to their nanoporosity-are specificities of these reservoirs, which challenge existing frameworks. Here we use molecular simulation and statistical models to show that recovery is hampered by interfacial effects at the wet kerogen surface. Recovery is shown to be thermally activated with an energy barrier modelled from the interface wetting properties. We build a statistical model of the recovery kinetics with a two-regime decline that is consistent with published data: a short time decay, consistent with Darcy description, followed by a fast algebraic decay resulting from increasingly unreachable energy barriers. Replacing water by CO2 or propane eliminates the barriers, therefore raising hopes for clean/efficient recovery.

}, doi = {10.1038/ncomms11890}, url = {http://www.nature.com/articles/ncomms11890}, author = {Lee, Thomas and Lyd{\'e}ric Bocquet and Benoit A. Coasne} } @article {217, title = {Effect of Water on Elastic and Creep Properties of Self-Standing Clay Films}, journal = {Langmuir}, volume = {32}, year = {2016}, month = {Feb-09-2016}, pages = {1370 - 1379}, abstract = {

We characterized experimentally the elastic and creep properties of thin self-standing clay films, and how their mechanical properties evolved with relative humidity and water content. The films were made of clay montmorillonite SWy-2, obtained by evaporation of a clay suspension. Three types of films were manufactured, which differed by their interlayer cation: sodium, calcium, or a mixture of sodium with calcium. The orientational order of the films was characterized by X-ray diffractometry. The films were mechanically solicited in tension, the resulting strains being measured by digital image correlation. We measured the Young\&$\#$39;s modulus and the creep over a variety of relative humidities, on a full cycle of adsorption-desorption for what concerns the Young\&$\#$39;s modulus. Increasing relative humidity made the films less stiff and made them creep more. Both the elastic and creep properties depended significantly on the interlayer cation. For the Young\&$\#$39;s modulus, this dependence must originate from a scale greater than the scale of the clay layer. Also, hysteresis disappeared when plotting the Young\&$\#$39;s modulus versus water content instead of relative humidity. Independent of interlayer cation and of relative humidity greater than 60\%, after a transient period, the creep of the films was always a logarithmic function of time. The experimental data gathered on these mesoscale systems can be of value for modelers who aim at predicting the mechanical behavior of clay-based materials (e.g., shales) at the engineering macroscopic scale from the one at the atomistic scale, for them to validate the first steps of their upscaling scheme. They provide also valuable reference data for bioinspired clay-based hybrid materials.

}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.5b03431}, author = {Benoit Carrier and Matthieu Vandamme and Roland Jean-Marc Pellenq and Bornert, Michel and Ferrage, Eric and Hubert, Fabien and Henri Van Damme} } @article {247, title = {Evolution of organo-clay composites with respect to thermal maturity in type II organic-rich source rocks}, journal = {Geochimica et Cosmochimica Acta}, volume = {195}, year = {2016}, month = {Dec-15-2016}, pages = {68 - 83}, abstract = {

Among the proposed pathways of sequestration and progressive transformation of organic matter (OM) during burial, the sorptive protection mechanism explains the strong relationship between total organic carbon (TOC) and mineral surface area (MSA) noted in numerous black shales around the globe. The complete mechanistic framework of preservation and evolution of OM in organo-mineral complexes remains, however, an enigma. On one hand, smectite layers composing the clay fraction are known to have a major influence on available surface area. OM maturation occurs, on the other hand, concurrently with the smectite illitization that provokes the closure of the interlayer spaces. The potential of smectite layers in the sequestration and preservation of organic molecules and the fate of these molecules with respect to the smectite illitization were therefore addressed. Here, the mineralogy of three organic-rich source rocks of various maturities was characterized in regards with the geochemistry of their OM. A thorough examination of the clay minerals present in the clay matrices provided evidences of mixed layer minerals containing smectite and illite layers with an increasing illite component with respect to maturity. The comprehensive interpretation of the X-ray diffractograms and analytical electron microscopy results suggested the presence of organic molecules in the inter-particulate and possibly the interlayer spaces of the smectite-rich components in immature source rocks. This eventuality was further supported by the presence of intercalated clay-organic nanocomposites observed by transmitted electron microscopy coupled with energy dispersive spectroscopy. Textural observations also showed that the increased illite content found in the overmature sample led to the reorganization of the OM and the clay particles into nano-scale aggregates. These results clarify the geochemical mechanism beyond the reported relationship between TOC and MSA and allow generalizing it to various organic-rich source rocks. Eventually, the understanding of the close organo-clay association raises prospects on the prediction of the evolution of the mechanical properties of economically valuable source rocks with respect to maturity.

}, issn = {00167037}, doi = {10.1016/j.gca.2016.09.008}, author = {Berthonneau, Jeremie and Grauby, Olivier and Muhannad Abuhaikal and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Henri Van Damme} } @article {248, title = {Fracture toughness anomalies: Viewpoint of topological constraint theory}, journal = {Acta Materialia}, volume = {121}, year = {2016}, month = {Dec-2016}, pages = {234 - 239}, abstract = {

The relationship between composition, structure, and resistance to fracture remains poorly understood. Here, based on molecular dynamics simulations, we report that sodium silicate glasses and calcium\–silicate\–hydrates feature an anomalous maximum in fracture toughness. In the framework of topological constraint theory, this anomaly is correlated to a flexible-to-rigid transition, driven by pressure or composition for sodium silicate and calcium\–silicate\–hydrates, respectively. This topological transition, observed for an isostatic network, is also shown to correspond to a ductile-to-brittle transition. At this state, the network is rigid but free of eigen-stress and features stress relaxation through crack blunting, resulting in optimal resistance to fracture. Our topological approach could therefore enable the computational design of tough inorganic solids, which has long been a \“holy grail\” within the non-metallic materials chemistry community.

Image 1

}, issn = {13596454}, doi = {10.1016/j.actamat.2016.09.004}, author = {Mathieu Bauchy and Wang, Bu and Wang, Mengyi and Yu, Yingtian and Mohammad Javad Abdolhosseini Qomi and Smedskjaer, Morten M. and Christophe Bichara and Franz-Josef Ulm and Roland Jean-Marc Pellenq} } @article {196, title = {Mesoscale texture of cement hydrates}, journal = {Proceedings of the National Academy of Sciences}, volume = {113}, year = {2016}, month = {Feb-23-2016}, pages = {2029 - 2034}, abstract = {

Strength and other mechanical properties of cement and concrete rely upon the formation of calcium\–silicate\–hydrates (C\–S\–H) during cement hydration. Controlling structure and properties of the C\–S\–H phase is a challenge, due to the complexity of this hydration product and of the mechanisms that drive its precipitation from the ionic solution upon dissolution of cement grains in water. Departing from traditional models mostly focused on length scales above the micrometer, recent research addressed the molecular structure of C\–S\–H. However, small-angle neutron scattering, electron-microscopy imaging, and nanoindentation experiments suggest that its mesoscale organization, extending over hundreds of nanometers, may be more important. Here we unveil the C\–S\–H mesoscale texture, a crucial step to connect the fundamental scales to the macroscale of engineering properties. We use simulations that combine information of the nanoscale building units of C\–S\–H and their effective interactions, obtained from atomistic simulations and experiments, into a statistical physics framework for aggregating nanoparticles. We compute small-angle scattering intensities, pore size distributions, specific surface area, local densities, indentation modulus, and hardness of the material, providing quantitative understanding of different experimental investigations. Our results provide insight into how the heterogeneities developed during the early stages of hydration persist in the structure of C\–S\–H and impact the mechanical performance of the hardened cement paste. Unraveling such links in cement hydrates can be groundbreaking and controlling them can be the key to smarter mix designs of cementitious materials.

Fig. 1.

}, issn = {0027-8424}, doi = {10.1073/pnas.1520487113}, author = {Katerina Ioannidou and Konrad J. Krakowiak and Mathieu Bauchy and Christian G. Hoover and Enrico Masoero and Sidney Yip and Franz-Josef Ulm and Pierre E. Levitz and Roland Jean-Marc Pellenq and Emanuela Del Gado} } @article {323, title = {Nanochemo-mechanical signature of organic-rich shales: a coupled indentation{\textendash}EDX analysis}, journal = {Acta Geotechnica}, volume = {11}, year = {2016}, month = {Jun-2016}, pages = {559 - 572}, abstract = {

The organic\–inorganic nature of organic-rich source rocks poses several challenges for the development of functional relations that link mechanical properties with geochemical composition. With this focus in mind, we herein propose a method that enables chemo-mechanical characterization of this highly heterogeneous source rock at the micron and submicron length scale through a statistical analysis of a large array of energy-dispersive X-ray spectroscopy (EDX) data coupled with nanoindentation data. The ability to include elemental composition to the indentation probe via EDX is shown to provide a means to identify pure material phases, mixture phases, and interfaces between different phases. Employed over a large array, the statistical clustering of this set of chemo-mechanical data provides access to the properties of the fundamental building blocks of clay-dominated organic-rich source rocks. The versatility of the approach is illustrated through the application to a large number of source rocks of different origin, chemical composition, and organic content. We find that the identified properties exhibit a unique scaling relation between stiffness and hardness. This suggests that organic-rich shale properties can be reduced to their elementary constituents, with several implications for the development of predictive functional relations between chemical composition and mechanical properties of organic-rich source rocks such as the intimate interplay between clay-packing, organic maturity, and mechanical properties of porous clay/organic phase.

}, issn = {1861-1125}, doi = {10.1007/s11440-015-0426-4}, author = {Abedi, Sara and Slim, Mirna and Hofmann, Ronny and Bryndzia, Taras and Franz-Josef Ulm} } @article {195, title = {Realistic molecular model of kerogen{\textquoteright}s nanostructure}, journal = {Nature Materials}, year = {2016}, month = {Feb-01-2016}, abstract = {

Despite kerogen\’s importance as the organic backbone for hydrocarbon production from source rocks such as gas shale, the interplay between kerogen\’s chemistry, morphology and mechanics remains unexplored. As the environmental impact of shale gas rises, identifying functional relations between its geochemical, transport, elastic and fracture properties from realistic molecular models of kerogens becomes all the more important. Here, by using a hybrid experimental\–simulation method, we propose a panel of realistic molecular models of mature and immature kerogens that provide a detailed picture of kerogen\’s nanostructure without considering the presence of clays and other minerals in shales. We probe the models\’ strengths and limitations, and show that they predict essential features amenable to experimental validation, including pore distribution, vibrational density of states and stiffness. We also show that kerogen\’s maturation, which manifests itself as an increase in the sp2/sp3 hybridization ratio, entails a crossover from plastic-to-brittle rupture mechanisms.

Kerogen in organic-rich shale formations.

Reconstruction of molecular models of kerogens.

Experimental validation of the molecular models.

Elastic properties of molecular models of kerogen.

}, issn = {1476-1122}, doi = {10.1038/nmat4541}, author = {Bousige, Colin and Ghimbeu, Cam{\'e}lia Matei and Vix-Guterl, Cathie and Pomerantz, Andrew E. and Suleimenova, Assiya and Vaughan, Gavin and Garbarino, Gaston and Feygenson, Mikhail and Wildgruber, Christoph and Franz-Josef Ulm and Roland Jean-Marc Pellenq and Benoit A. Coasne} } @article {270, title = {Scaling behaviour of cohesive granular flows}, journal = {EPL (Europhysics Letters)}, volume = {112}, year = {2016}, month = {Jan-12-2016}, pages = {Article Number: 64004}, abstract = {

The shear strength of dense granular flows is generally described by an effective friction coefficient, ratio of shear to normal stress, as a function of the inertial number I. However, this ratio depends on the normal stress when the particles interact via both friction and adhesion forces, and in this sense it does not properly represent a Coulomb-like friction. For the same reason, it is not a unique function of I. We used extensive contact dynamics simulations to isolate the cohesive strength from the purely frictional strength in dense inertial flows for a broad range of shear rates and adhesion forces between particles. Remarkably, while the frictional part of the strength increases with I, the cohesive strength is found to be a decreasing function of I. We show that a single dimensionless parameter, combining interparticle adhesion with I, controls not only the cohesive strength but also the packing fraction and granular texture in inertial flows.

}, issn = {0295-5075}, doi = {10.1209/0295-5075/112/64004}, author = {Berger, Nicolas and Emilien Az{\'e}ma and Douce, Jean-Fran{\c c}ois and Farhang Radja{\"\i}} } @article {619, title = {Spectroscopic probe of the van der Waals interaction between polar molecules and a curved surface}, journal = {Physical Review A}, volume = {94}, year = {2016}, month = {Aug-17-2016}, abstract = {

We study the shift of rotational levels of a diatomic polar molecule due to its van der Waals interaction with a gently curved dielectric surface at temperature T, and submicron separations. The molecule is assumed to be in its electronic and vibrational ground state, and the rotational degrees are described by a rigid rotor model. We show that under these conditions retardation effects and surface dispersion can be neglected. The level shifts are found to be independent of T, and given by the quantum state averaged classical electrostatic interaction of the dipole with its image on the surface. We use a derivative expansion for the static Green\&$\#$39;s function to express the shifts in terms of surface curvature. We argue that the curvature induced line splitting is experimentally observable, and not obscured by natural linewidths and thermal broadening.

}, issn = {2469-9926}, doi = {10.1103/PhysRevA.94.022509}, url = {https://link.aps.org/doi/10.1103/PhysRevA.94.022509}, author = {Bimonte, Giuseppe and Emig, Thorsten and Jaffe, R. L. and Kardar, Mehran} } @article {326, title = {Velocity statistics of the Nagel-Schreckenberg model}, journal = {Physical Review E}, volume = {93}, year = {2016}, month = {Feb-18-2016}, pages = {Article Number: 022305}, abstract = {

The statistics of velocities in the cellular automaton model of Nagel and Schreckenberg for traffic are studied. From numerical simulations, we obtain the probability distribution function (PDF) for vehicle velocities and the velocity-velocity (vv) correlation function. We identify the probability to find a standing vehicle as a potential order parameter that signals nicely the transition between free congested flow for sufficiently large number of velocity states. Our results for the vv correlation function resemble features of a second order phase transition. We develop a 3-body approximation that allows us to relate the PDFs for velocities and headways. Using this relation, an approximation to the velocity PDF is obtained from the headway PDF observed in simulations. We find a remarkable agreement between this approximation and the velocity PDF obtained from simulations.

}, issn = {2470-0045}, doi = {10.1103/PhysRevE.93.022305}, author = {Bain, Nicolas and Emig, Thorsten and Franz-Josef Ulm and Schreckenberg, Michael} } @article {177, title = {Assessing Polarizability Models for the Simulation of Low-Frequency Raman Spectra of Benzene}, journal = {The Journal of Physical Chemistry B}, volume = {119}, year = {2015}, month = {Jul-23-2015}, pages = {9345 - 9358}, abstract = {
Abstract Image

Optical Kerr effect (OKE) spectroscopy is a widely used technique for probing the low-frequency, Raman-active dynamics of liquids. Although molecular simulations are an attractive tool for assigning liquid degrees of freedom to OKE spectra, the accurate modeling of the OKE and the motions that contribute to it relies on the use of a realistic and computationally tractable molecular polarizability model. Here we explore how the OKE spectrum of liquid benzene, and the underlying dynamics that determines its shape, are affected by the polarizability model employed. We test a molecular polarizability model that uses a point anisotropic molecular polarizability and three other models that distribute the polarizability over the molecule. The simplest and most computationally efficient distributed polarizability model tested is found to be sufficient for the accurate simulation of the many-body polarizability dynamics of this liquid. We further find that the atomic-to-molecular polarizability transformation approximation [Hu et al. J. Phys. Chem. B 2008, 112, 7837\–7849], used in conjunction with this distributed polarizability model, yields OKE spectra whose shapes differ negligibly from those calculated without this approximation, providing a substantial increase in computational efficiency.

}, issn = {1520-6106}, doi = {10.1021/jp509968v}, author = {Bender, John S. and Benoit A. Coasne and Fourkas, John T.} } @article {128, title = {Bottom-up model of adsorption and transport in multiscale porous media.}, journal = {Phys Rev E Stat Nonlin Soft Matter Phys}, volume = {91}, year = {2015}, month = {Mar-20-2015}, pages = {Article Number: 032133 }, abstract = {

We develop a model of transport in multiscale porous media which accounts for adsorption in the different porosity scales. This model employs statistical mechanics to upscale molecular simulation and describe adsorption and transport at larger time and length scales. Using atom-scale simulations, which capture the changes in adsorption and transport with temperature, pressure, pore size, etc., this approach does not assume any adsorption or flow type. Moreover, by relating the local chemical potential \μ(r) and density \ρ(r), the present model accounts for adsorption effects and possible changes in the confined fluid state upon transport. This model constitutes a bottom-up framework of adsorption and transport in multiscale materials as it (1) describes the adsorption-transport interplay, (2) accounts for the hydrodynamics breakdown at the nm scale, and (3) is multiscale.

}, issn = {1550-2376}, doi = {10.1103/PhysRevE.91.032133}, author = {Botan, Alexandru and Franz-Josef Ulm and Roland Jean-Marc Pellenq and Benoit A. Coasne} } @article {136, title = {Capturing material toughness by molecular simulation: accounting for large yielding effects and limits}, journal = {International Journal of Fracture}, volume = {194}, year = {2015}, month = {Aug-2015}, pages = {149 - 167}, abstract = {

The inherent computational cost of molecular simulations limits their use to the study of nanometric systems with potentially strong size effects. In the case of fracture mechanics, size effects due to yielding at the crack tip can affect strongly the mechanical response of small systems. In this paper we consider two examples: a silica crystal for which yielding is limited to a few atoms at the crack tip, and a nanoporous polymer for which the process zone is about one order of magnitude larger. We perform molecular simulations of fracture of those materials and investigate in particular the system and crack size effects. The simulated systems are periodic with an initial crack. Quasi-static loading is achieved by increasing the system size in the direction orthogonal to the crack while maintaining a constant temperature. As expected, the behaviors of the two materials are significantly different. We show that the behavior of the silica crystal is reasonably well described by the classical framework of linear elastic fracture mechanics (LEFM). Therefore, one can easily upscale engineering fracture properties from molecular simulation results. In contrast, LEFM fails capturing the behavior of the polymer and we propose an alternative analysis based on cohesive crack zone models. We show that with a linear decreasing cohesive law, this alternative approach captures well the behavior of the polymer. Using this cohesive law, one can anticipate the mechanical behavior at larger scale and assess engineering fracture properties. Thus, despite the large yielding of the polymer at the scale of the molecular simulation, the cohesive zone analysis offers a proper upscaling methodology.

}, issn = {0376-9429}, doi = {10.1007/s10704-015-0045-y}, author = {Brochard, Laurent and Gy{\"o}rgy Hantal and Hadrien Laubie and Franz-Josef Ulm and Roland Jean-Marc Pellenq and Benoit A. Coasne} } @article {158, title = {Casimir-Polder force between anisotropic nanoparticles and gently curved surfaces}, journal = {Physical Review D}, volume = {92}, year = {2015}, month = {Jul-17-2015}, abstract = {

The Casimir--Polder interaction between an anisotropic particle and a surface is orientation dependent. We study novel orientational effects that arise due to curvature of the surface for distances much smaller than the radii of curvature by employing a derivative expansion. For nanoparticles we derive a general short distance expansion of the interaction potential in terms of their dipolar polarizabilities. Explicit results are presented for nano-spheroids made of SiO2 and gold, both at zero and at finite temperatures. The preferred orientation of the particle is strongly dependent on curvature, temperature, as well as material properties.

}, issn = {1550-7998}, doi = {10.1103/PhysRevD.92.025028}, author = {Bimonte, Giuseppe and Emig, Thorsten and Kardar, Mehran} } @proceedings {98, title = {Is cement a glassy material?}, journal = {Euro-C Conference}, volume = {COMPUTATIONAL MODELLING OF CONCRETE STRUCTURES, VOL 1}, year = {2015}, month = {Jun-22-2015}, pages = {169-176}, publisher = {CRC PRESS-TAYLOR \& FRANCIS GROUP}, address = {MAR 24-27, 2014, St Anton am Alberg, AUSTRIA}, abstract = {

The nature of Calcium-Silicate-Hydrate (C-S-H), the binding phase of cement, remains a controversial question. In particular, contrary to the former crystalline model, it was recently proposed that its nanoscale structure was actually amorphous. To elucidate this issue, we analyzed the structure of a realistic simulation of C-S-H, and compared the latter to crystalline tobermorite, a natural analogue to cement, and to an artificial ideal glass. Results clearly support that C-S-H is amorphous. However, its structure shows an intermediate degree of order, retaining some characteristics of the crystal while acquiring an overall glass-like disorder. Thanks to a detailed quantification of order and disorder, we show that its amorphous state mainly arises from its hydration.

}, isbn = {978-1-138-02641-4; 978-1-315-76203-6}, doi = {10.1201/b16645-19}, author = {Mathieu Bauchy and Mohammad Javad Abdolhosseini Qomi and Roland Jean-Marc Pellenq and Franz-Josef Ulm}, editor = {Bicanic, N and Mang, H and Meschke, G and DeBorst, R} } @proceedings {332, title = {Creep of Bulk C-S-H: Insights from Molecular Dynamics Simulations}, journal = {10th International Conference on Mechanics and Physics of Creep, Shrinkage, and Durability of Concrete and Concrete StructuresCONCREEP 10}, volume = {CONCREEP 10: MECHANICS AND PHYSICS OF CREEP, SHRINKAGE, AND DURABILITY OF CONCRETE AND CONCRETE STRUCTURES }, year = {2015}, month = {Sep-17-2015}, pages = {511-516}, publisher = {American Society of Civil Engineers}, address = {September 21{\textendash}23, 2015, Vienna, AustriaReston, VA}, abstract = {

Understanding the physical origin of creep in calcium\–silicate\–hydrate (C\–S\–H) is of primary importance, both for fundamental and practical interest. Here, we present a new method, based on molecular dynamics simulation, allowing us to simulate the long-term visco-elastic deformations of C\–S\–H. Under a given shear stress, C\–S\–H features a gradually increasing shear strain, which follows a logarithmic law. The computed creep modulus is found to be independent of the shear stress applied and is in excellent agreement with nanoindentation measurements, as extrapolated to zero porosity.

}, doi = {10.1061/978078447934610.1061/9780784479346.061}, author = {Mathieu Bauchy and Enrico Masoero and Franz-Josef Ulm and Roland Jean-Marc Pellenq}, editor = {Hellmich, Christian and Pichler, Bernhard and Kollegger, Johann} } @proceedings {331, title = {C-S-H across Length Scales: From Nano to Micron}, journal = {10th International Conference on Mechanics and Physics of Creep, Shrinkage, and Durability of Concrete and Concrete StructuresCONCREEP 10}, volume = {CONCREEP 10: MECHANICS AND PHYSICS OF CREEP, SHRINKAGE, AND DURABILITY OF CONCRETE AND CONCRETE STRUCTURES }, year = {2015}, month = {Sep-17-2015}, pages = {39-48}, publisher = {American Society of Civil Engineers}, address = {September 21{\textendash}23, 2015, Vienna, AustriaReston, VA}, abstract = {

Despite their impact on longevity, serviceability, and environmental footprint of our built infrastructure, the chemo-physical origins of nanoscale properties of cementitious materials, and their link to macroscale properties still remain rather obscure. Here, we discuss a multi-scale approach that describes different aspects of physical properties of C-S-H at the nano- and meso-scales. These include dynamics of water, thermal properties and mechanical behavior of C-S-H and its effect on properties of cement paste at different scales.

}, doi = {10.1061/978078447934610.1061/9780784479346.006}, url = {http://ascelibrary.org/doi/book/10.1061/9780784479346http://ascelibrary.org/doi/pdf/10.1061/9780784479346http://ascelibrary.org/doi/10.1061/9780784479346.006http://ascelibrary.org/doi/pdf/10.1061/9780784479346.006}, author = {Mohammad Javad Abdolhosseini Qomi and Enrico Masoero and Mathieu Bauchy and Franz-Josef Ulm and Emanuela Del Gado and Roland Jean-Marc Pellenq}, editor = {Hellmich, Christian and Pichler, Bernhard and Kollegger, Johann} } @article {163, title = {Diffusion of Interlayer Cations in Swelling Clays as a Function of Water Content: Case of Montmorillonites Saturated with Alkali Cations}, journal = {The Journal of Physical Chemistry C}, volume = {119}, year = {2015}, month = {May-14-2015}, pages = {10370 - 10378}, abstract = {
Abstract Image

Swelling clays act as ion-exchange membranes owing to the presence of extra-framework ions surrounded by water molecules. A better understanding of the motion of the ions present in the pore space is required to predict the diffusion properties in these solids. Since water molecules tend to adsorb both on ions and clay surfaces, they moderate the interactions between the ions and the framework. The hydration of ions therefore has an impact on their diffusion properties. In this paper, the MX-80 montmorillonite considered for nuclear waste disposal applications has been selected and studied using an approach combining measurements of complex impedance spectroscopy and water adsorption isotherms. The number of charge carriers has been estimated, and the diffusion coefficient for interlayer cations at various hydration states was determined. The evolution of the diffusion coefficient is subsequently correlated with the effect of the opening of the interlayer space and its hydration state. The resulting picture sheds light on the reversible or irreversible character of ion exchange. Finally, our results obtained from the difference between the interlayer diffusion coefficients extracted from conductivity measurements and those obtained at the macroscopic scale is discussed in terms of the textural parameters.

}, issn = {1932-7447}, doi = {10.1021/jp512986d}, author = {Salles, Fabrice and Douillard, Jean-Marc and Bildstein, Olivier and El Ghazi, Samira and Prelot, B{\'e}n{\'e}dicte and Zajac, Jerzy and Henri Van Damme} } @proceedings {343, title = {Evolution of particle size distributions in crushable granular materials}, journal = {3rd International Symposium on Geomechanics from Micro to Macro}, volume = {Geomechanics from Micro to Macro}, year = {2015}, month = {Feb-02-2015}, pages = {275 - 280}, publisher = {CRC Press}, address = {SEP 01-03-2014 Univ Cambridge, Cambridge, ENGLAND}, abstract = {

By means of the contact dynamics method together with a particle fracture model, in which the particles are cohesive aggregates of irreducible polygonal fragments, we investigate the evolution of particle size distribution in the process of uniaxial compaction of granular materials. The case of single particle breakup under compressive stress is used to test the method and the influence of discretization (number of irreducible fragments). We show that the breaking threshold of the granular assembly scales with the internal cohesion of the particles but it depends also on the initial size distribution and irregularity of polygonal particle shapes. The evolution of size distribution proceeds by consecutive periods of intense particle crushing, characterized by local shattering instability, and periods of little breaking activity. Starting with either monodisperse or power-law distribution of particle sizes, the latter evolves towards a broad distribution of the fragmented particles with a nearly power-law distribution in the range of intermediate particle sizes. Interestingly, a finite number of large particles survive despite ongoing crushing process due to the more homogeneous distribution of forces in the presence of small fragmented particles filling the pores between larger particles.

}, isbn = {978-1-138-02707-7}, doi = {10.1201/b1739510.1201/b17395-48}, author = {Duc-Hanh Nguyen and Emilien Az{\'e}ma and Farhang Radja{\"\i} and Philippe Sornay}, editor = {Kenichi Soga and Krishna Kumar and Giovanna Biscontin and Kuo, Matthew} } @article {137, title = {Fracture toughness of calcium{\textendash}silicate{\textendash}hydrate from molecular dynamics simulations}, journal = {Journal of Non-Crystalline Solids}, volume = {419}, year = {2015}, month = {Jul-01-2015}, pages = {58 - 64}, abstract = {

Concrete is the most widely manufactured material in the world. Its binding phase, calcium\–silicate\–hydrate (C\–S\–H), is responsible for its mechanical properties and has an atomic structure fairly similar to that of usual calcium silicate glasses, which makes it appealing to study this material with tools and theories traditionally used for non-crystalline solids. Here, following this idea, we use molecular dynamics simulations to evaluate the fracture toughness of C\–S\–H, inaccessible experimentally. This allows us to discuss the brittleness of the material at the atomic scale. We show that, at this scale, C\–S\–H breaks in a ductile way, which prevents one from using methods based on linear elastic fracture mechanics. Knowledge of the fracture properties of C\–S\–H at the atomic scale opens the way for an upscaling approach to the design of tougher cement paste, which would allow for the design of slender environment-friendly infrastructures, requiring less material.

}, issn = {00223093}, doi = {10.1016/j.jnoncrysol.2015.03.031}, author = {Mathieu Bauchy and Hadrien Laubie and Mohammad Javad Abdolhosseini Qomi and Christian G. Hoover and Franz-Josef Ulm and Roland Jean-Marc Pellenq} } @article {159, title = {Interplay of curvature and temperature in the Casimir{\textendash}Polder interaction}, journal = {Journal of Physics: Condensed Matter}, volume = {27}, year = {2015}, month = {Jun-03-2015}, pages = {214018}, abstract = {

We study the Casimir-Polder interaction at finite temperatures between a polarizable small, anisotropic particle and a non-planar surface using a derivative expansion. We obtain the leading and the next-to-leading curvature corrections to the interaction for low and high temperatures. Explicit results are provided for the retarded limit in the presence of a perfectly conducting surface.

}, issn = {0953-8984}, doi = {10.1088/0953-8984/27/21/214018}, author = {Bimonte, Giuseppe and Emig, Thorsten} } @proceedings {334, title = {Kinetic Simulations of Cement Creep: Mechanisms from Shear Deformations of Glasses}, journal = {10th International Conference on Mechanics and Physics of Creep, Shrinkage, and Durability of Concrete and Concrete StructuresCONCREEP 10}, volume = {CONCREEP 10: MECHANICS AND PHYSICS OF CREEP, SHRINKAGE, AND DURABILITY OF CONCRETE AND CONCRETE STRUCTURES}, year = {2015}, month = {Sep-17-2015}, pages = {555-564}, publisher = {American Society of Civil Engineers}, address = {September 21{\textendash}23, 2015, Vienna, AustriaReston, VA}, abstract = {

The logarithmic deviatoric creep of cement paste is a technical and scientific challenge. Transition State Theory (TST) indicates that some nanoscale mechanisms of shear deformation, associated with a specific kind of strain hardening, can explain the type of deviatoric creep observed experimentally in mature cement pastes. To test this possible explanation, we simulate the shear deformations of a colloidal model of cement hydrates at the nanoscale. Results from quasi-static simulations indicate a strain hardening analogous to that postulated by the TST approach. Additional results from oscillatory shear (fatigue) simulations show an increase of deformation with number of loading cycles that is consistent with the observed creep. These findings indicate that nanoscale simulations can improve our current understanding of the mechanisms underlying creep, with potential to go beyond the logarithmic creep and explore the onset of failure during tertiary creep.

}, doi = {10.1061/978078447934610.1061/9780784479346.068}, author = {Enrico Masoero and Mathieu Bauchy and Emanuela Del Gado and Hegoi Manzano and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Sidney Yip}, editor = {Hellmich, Christian and Pichler, Bernhard and Kollegger, Johann} } @proceedings {358, title = {Micromechanical analysis of the surface erosion of a cohesive soil by means of a coupled LBM-DEM model}, journal = {IV International Conference on Particle-based Methods (PARTICLES 2015)}, volume = {PARTICLE-BASED METHODS IV-FUNDAMENTALS AND APPLICATIONS}, year = {2015}, month = {sept-30-2015}, pages = {519-528}, publisher = {International Center for Numerical Methods in Engineering (CIMNE)}, address = {SEP 28-30 2015 Barcelona, SPAIN}, abstract = {

The elementary mechanisms driving the ubiquitous surface erosion of cohesive geomaterials can be analysed from a micromechanical perspective combining well-known numerical techniques. Here, a coupled model combining the Discrete Element and Lattice Boltzmann methods (DEM-LBM) provides an insight into the solid-fluid interaction during the transient erosion caused by a vertical fluid jet impinging on the surface of a granular assembly. The brittle cementation providing cohesion between the solid grains is described here by means of a simple bond model with a single-parameter yield surface. The initial topology of the surface erosion tends to mimic the profile of fluid velocity directly above the soil surface. We find that both the rate of erosion and the magnitude of eroded mass depend directly on the micromechanical strength of the single solid bonds.

}, keywords = {Cohesion, DEM, LBM, Surface erosion}, url = {https://hal.archives-ouvertes.fr/hal-01269324}, author = {Cuellar, Pablo and Pierre Philippe and St{\'e}phane Bonelli and Benahmed, Nadia and Brunier-Coulin, Florian and Jeff Ngoma and Jean-Yves Delenne and Farhang Radja{\"\i}}, editor = {Onate, E and Bischoff, M and Owen, DRJ} } @article {625, title = {Native Morphology of Hydrated Spheroidal Halloysite Observed by Environmental Transmission Electron Microscopy}, journal = {Clays and Clay Minerals}, volume = {63}, year = {2015}, month = {Oct-2015}, pages = {368 - 377}, abstract = {

Natural mineral materials such as tabular and spheroidal halloysites have recently been suggested as candidates for intercalating metal ions or organic molecules. Their potential use as nano-adsorbents is related to their porous structure and water content. Although the two morphologies can coexist in natural deposits, spheroidal halloysites remain poorly characterized whereas much literature exists on tubular halloysites. The present study investigates the native morphology, internal porous structure, and behavior upon dehydration of spheroidal halloysite from Opotiki (New Zealand). This mineral was characterized in its natural hydrated state using a transmission electron microscope equipped with an environmental cell (EC-TEM). The sample was placed in a sealed block in which water vapor-saturated air circulated at a pressure of 30 Torr. The observed particles consisted of almost complete spheroids displaying polyhedral external surfaces. 1:1 layers stack concentrically as a pore-free, onion-like structure. The dynamic processes of dehydration created by slow depressurization of the cell resulted in a decrease in the layer-to-layer distance (d001) from ~10 \Å to ~7 \Å due to the loss of interlayer water molecules. Irreversible formation of spurious \‘internal pores\’ was recorded during this process. These pores were not indigenous to the hydrated 10 \Å halloysite and resulted from the collapse of the native layers. They cannot account for the physical chemical properties of spheroidal halloysite. Spheroidal halloysites would have a lower propensity for intercalating ions or molecules than tubular halloysites. Isolated facets were also observed in high-resolution-TEM and displayed a pseudo-hexagonal morphology. The three-dimensional microstructure of the spheroid appeared bent along the three pseudo equivalent yi directions of the kaolinite-like single layers. An analogy with polyhedral serpentine has allowed the proposal of a formation process of hydrated spheroidal halloysite triggered by enrichment in divalent ions in the growth system.

}, issn = {00098604}, doi = {10.1346/CCMN.2015.0630503}, url = {http://openurl.ingenta.com/content/xref?genre=article\&issn=0009-8604\&volume=63\&issue=5\&spage=368}, author = {Berthonneau, Jeremie and Grauby, Olivier and Jeannin, Charlotte and Chaudanson, Damien and Joussein, Emmanuel and Alain Baronnet} } @article {142, title = {Optimized molecular reconstruction procedure combining hybrid reverse Monte Carlo and molecular dynamics}, journal = {The Journal of Chemical Physics}, volume = {142}, year = {2015}, month = {Mar-21-2015}, pages = {Article Number: 114112}, abstract = {

We report an efficient atom-scale reconstruction method that consists of combining the Hybrid Reverse Monte Carlo algorithm (HRMC) with Molecular Dynamics (MD) in the framework of a simulated annealing technique. In the spirit of the experimentally constrained molecular relaxation technique [Biswas et al., Phys. Rev. B 69, 195207 (2004)], this modified procedure offers a refined strategy in the field of reconstruction techniques, with special interest for heterogeneous and disordered solids such as amorphous porous materials. While the HRMC method generates physical structures, thanks to the use of energy penalties, the combination with MD makes the method at least one order of magnitude faster than HRMC simulations to obtain structures of similar quality. Furthermore, in order to ensure the transferability of this technique, we provide rational arguments to select the various input parameters such as the relative weight of the energy penalty with respect to the structure optimization. By applying the method to disordered porous carbons, we show that adsorption properties provide data to test the global texture of the reconstructed sample but are only weakly sensitive to the presence of defects. In contrast, the vibrational properties such as the phonon density of states are found to be very sensitive to the local structure of the sample.

Image of FIG. 1.

Image of FIG. 2.

Image of FIG. 3.

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}, issn = {0021-9606}, doi = {10.1063/1.4914921}, author = {Bousige, Colin and Botan, Alexandru and Franz-Josef Ulm and Roland Jean-Marc Pellenq and Benoit A. Coasne} } @article {141, title = {Organic{\textendash}Clay Interfacial Chemical Bonds Probed by ab Initio Calculations}, journal = {The Journal of Physical Chemistry C}, volume = {119}, year = {2015}, month = {Mar-26-2015}, pages = {6511 - 6517}, abstract = {
Abstract Image

Evaluating the nature of binding of the organic phase (called kerogen) with clays and other minerals in gas and oil shale is of critical importance for developing optimal processes for hydrocarbon extraction and recovery. Here we report the results of an ab initio reactive study of a gaseous oil/clay interface, which consists of grafting fragments of sp3 methane and sp2 benzene onto the basal surface of illite. Methane and benzene fragments were selected as they correspond to the simplest monomers of the immature (aliphatic sp3 carbon atoms) and mature (aromatic sp2 carbon atoms) stages of the kerogen macromolecule while illite is encountered in many shale formations. We find that the methyl or phenyl radicals always bond upright to one of the outmost Si atoms of the clay phase, while the H atom attaches to the inner Al\–OH group forming a water molecule. The covalent attachment of the radicals to the oxygen atoms of the clay surface is always less favorable than to the silicon atoms. The energetics of these grafted adducts are discussed along with the maturation state of the shale. An unanticipated signature of the covalent Si\–C binding is the formation of hypervalent Si complexes, characterized by elongated bonds at the oil/clay interface. We complement our atomistic modeling by simulating IR spectra of the two covalently grafted interfaces (methyl\–illite and phenyl\–illite) which fingerprint elongated Si\–C bonds in the frequency range 1100\–1250 cm\–1. This novel finding should have a large impact on the understanding of fracking conditions in shales through this tight- and loose-bonded organic/inorganic interface.

}, issn = {1932-7447}, doi = {10.1021/jp510885f}, author = {Bocquet, Marie-Laure and Benoit A. Coasne and Roland Jean-Marc Pellenq and Franz-Josef Ulm} } @article {178, title = {Polarized Water Wires under Confinement in Chiral Channels}, journal = {The Journal of Physical Chemistry B}, volume = {119}, year = {2015}, month = {Jul-16-2015}, pages = {8707 - 8717}, abstract = {
Abstract Image

The alignment of water molecules along chiral pores may activate proton/ion conduction along dipolar hydrophilic pathways. Here we show that a simple synthetic \“T-channel\” forms a directional pore with its carbonyl moieties solvated by chiral helical water wires. Atom-scale simulations and experimental crystallographic assays reveal a dynamical structure of water and electrolyte solutions (alkali metal chlorides) confined in these organic T-channels. Oscillations in the dipole orientation, which correspond to alternative ordering (dipole up\–dipole down) of the water molecules with a period of about 4.2 \Å (imposed by the distance between two successive carbonyl groups) are observed. When ions are added to the system, despite the strong Coulombic water/ion interaction, confined water remains significantly ordered in the T-channel and still exhibits surface-induced polarization. Cation permeation can be achieved through alternated hydration\–dehydration occurring along strongly oriented water wires. The T-channel, which exhibits chirality with strong water orientation, provides an opportunity to unravel novel water-channel systems that share many interesting properties of biomolecular systems.

}, issn = {1520-6106}, doi = {10.1021/acs.jpcb.5b03322}, author = {Barboiu, Mihail and Pierre-Andre Cazade and Le Duc, Yann and Yves-Marie Legrand and Arie Van Der Lee and Benoit A. Coasne} } @article {181, title = {Predicting Adsorption on Bare and Modified Silica Surfaces}, journal = {The Journal of Physical Chemistry C}, volume = {119}, year = {2015}, month = {Mar-19-2015}, pages = {6009 - 6017}, abstract = {
Abstract Image

We show that Derjaguin\’s theory of adsorption can be used to predict adsorption on bare and modified surfaces using parameters available to simple experiments. Using experiment and molecular simulation of adsorption of various gases on hydroxylated, methylated, and trifluoromethylated silica, this simple parametrization of Derjaguin\’s model allows predicting adsorption on any functionalized surface using a minimum set of parameters such as the heat of vaporization of the adsorbate and the Henry constant of the adsorption isotherm. This general yet simple scheme constitutes a powerful tool as it avoids having to carry out tedious and complex adsorption measurements.

}, issn = {1932-7447}, doi = {10.1021/jp511726a}, author = {L{\'e}pinay, Matthieu and Broussous, Lucile and Licitra, Christophe and Bertin, Fran{\c c}ois and Rouessac, Vincent and Ayral, Andre and Benoit A. Coasne} } @article {174, title = {Probing the microporosity of low-k organosilica films: MP and t-plot methods applied to ellipsometric porosimetry data}, journal = {Microporous and Mesoporous Materials}, volume = {217}, year = {2015}, month = {Nov-15-2015}, pages = {119 - 124}, abstract = {

Ellipsometric porosimetry (EP) experiments are performed to obtain the adsorption isotherms of water, methanol, and toluene on pristine and damaged SiOCH porous materials. The use of gaseous adsorbates with different polarities, sizes, and surface tensions enables us to probe their affinity with such organosilica surfaces. Using reference t-curves obtained from Statistical Mechanics molecular simulations, we discuss the ability of the MicroPore analysis (MP) method to accurately estimate micropore sizes from EP measurements by comparing them with the mean pore sizes obtained using positron annihilation lifetime spectroscopy (PALS) and grazing incidence small angle X-ray scattering (GISAXS). We also report accessible microporous volumes estimated from the t-plot method used with the reference t-curves obtained by means of molecular simulation. We show that EP characterization of microporous films combined with the MP and t-plot methods can be improved by taking into account the effect of the chemical nature of the pore surface on the variation of the adsorbed thickness (t-curve).

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}, issn = {13871811}, doi = {10.1016/j.micromeso.2015.05.050}, author = {L{\'e}pinay, Matthieu and Broussous, Lucile and Licitra, Christophe and Bertin, Fran{\c c}ois and Rouessac, Vincent and Ayral, Andre and Benoit A. Coasne} } @article {160, title = {Reversing the critical Casimir force by shape deformation}, journal = {Physics Letters B}, volume = {743}, year = {2015}, month = {Apr-09-2015}, pages = {138 - 142}, abstract = {

The exact critical Casimir force between periodically deformed boundaries of a 2D semi-infinite strip is obtained for conformally invariant classical systems. Only two parameters (conformal charge and scaling dimension of a boundary changing operator), along withthe solution of an electrostatic problem, determine the Casimir force, rendering the theory practically applicable to any shape and arrangement. The attraction between any two mirror symmetric objects follows directly from our general result. The possibility of purely shape induced reversal of the force, as well as occurrence of stable equilibrium points, is demonstrated for certain conformally invariant models, including the tricritical Ising model.

}, issn = {03702693}, doi = {10.1016/j.physletb.2015.02.038}, author = {Bimonte, Giuseppe and Emig, Thorsten and Kardar, Mehran} } @proceedings {357, title = {Rheology and Micromechanical Analysis of Granular Media Composed of Platy Particles: A Step Toward the DEM Simulation of Clayey Soils}, journal = {15th Pan-American Conference on Soil Mechanics and Geotechnical Engineering (PCSMGE) / 8th South American Congress on Rock Mechanics (SCRM)}, volume = {FROM FUNDAMENTALS TO APPLICATIONS IN GEOTECHNICS }, year = {2015}, month = {2015}, pages = {1357-1364}, address = {NOV 15-18 2015 Buenos Aires, ARGENTINA}, abstract = {

This work was carried out in the framework of a larger project devoted
to the micro-mechanical modeling of clayey soils by means of discrete element
simulations. Here, we study the rheology and microstructure of granular media
composed of platy particles. The particles are three-dimensional square plates,
approximated as spheropolyhedra. Several samples composed of particles of
different levels of platyness (related to the ratio of length to thickness) were
numerically prepared and sheared up to large deformations. Specifically, we
revisit and analyze in detail an ordering phenomenon described briefly in a
previous paper [1] and investigate its consequences in terms of the alignment of
particles and cluster formation. We find that particle alignment is strongly
enhanced by the degree of platyness and leads to the formation of face-connected
clusters. Due to dynamics, this spontaneous clustering is a robust characteristic of
granular systems composed of platy particles even in the absence of attraction
forces.

}, doi = {10.3233/978-1-61499-603-3-1357}, author = {Boton, Mauricio and Estrada, Nicolas and Emilien Az{\'e}ma}, editor = {Manzanal, D and Sfriso, AO} } @article {131, title = {Rigidity transition in materials: hardness is driven by weak atomic constraints.}, journal = {Phys Rev Lett}, volume = {114}, year = {2015}, month = {Mar-23-2015}, pages = {Article Number: 125502}, abstract = {

Understanding the composition dependence of the hardness in materials is of primary importance for infrastructures and handled devices. Stimulated by the need for stronger protective screens, topological constraint theory has recently been used to predict the hardness in glasses. Herein, we report that the concept of rigidity transition can be extended to a broader range of materials than just glass. We show that hardness depends linearly on the number of angular constraints, which, compared to radial interactions, constitute the weaker ones acting between the atoms. This leads to a predictive model for hardness, generally applicable to any crystalline or glassy material.

Figure

Figure

Figure

Figure

}, issn = {1079-7114}, doi = {10.1103/PhysRevLett.114.125502}, author = {Mathieu Bauchy and Mohammad Javad Abdolhosseini Qomi and Christophe Bichara and Franz-Josef Ulm and Roland Jean-Marc Pellenq} } @book {647, title = {Springer Series in Materials ScienceMolecular Dynamics Simulations of Disordered MaterialsFirst-Principles Modeling of Binary Chalcogenides: Recent Accomplishments and New Achievements}, volume = {215}, year = {2015}, pages = {313 - 344}, publisher = {Springer International Publishing}, organization = {Springer International Publishing}, address = {Cham}, abstract = {

This contribution is focussed on a set of first-principles molecular dynamics results obtained over the past fifteen years for disordered chalcogenides. In the first part, we sketch and review the historical premises underlying research efforts devoted to the understanding of structural properties in liquid and glassy GexSe1-x systems. We stress the importance of selecting well performing exchange-correlation functionals (within density functional theory) to achieve a correct description of short and intermediate range order. In the second part, we provide a specific, comparative example of structural analysis for chalcogenide GeX4 systems differing by the chemical identity of the X atom. We are able to demonstrate that the correct account of differences between the coordination environments of the two corresponding glasses requires system sizes substantially larger than similar to 100 atoms.

}, isbn = {978-3-319-15674-3}, issn = {0933-033X}, doi = {10.1007/978-3-319-15675-010.1007/978-3-319-15675-0_12}, url = {http://link.springer.com/10.1007/978-3-319-15675-0}, author = {Bouzid, A. and Le Roux, S. and Guido Ori and Tugene, Christine and Boero, M. and Carlo Massobrio}, editor = {Carlo Massobrio and Du, Jincheng and Bernasconi, Marco and Salmon, Philip S.} } @book {648, title = {Springer Series in Materials ScienceMolecular Dynamics Simulations of Disordered MaterialsMolecular Modeling of Glassy Surfaces}, volume = {215}, year = {2015}, pages = {345 - 365}, publisher = {Springer International Publishing}, organization = {Springer International Publishing}, address = {Cham}, abstract = {

Progress in computational materials science has allowed the development of realistic models for a wide range of materials including both crystalline and glassy solids. In recent years, with the growing interest in nanoparticles and porous materials, more attention has been devoted to the design of realistic models of glassy surfaces and finely divided materials. The structural disorder in glassy surfaces, however, poses a major challenge which consists of describing such surfaces using computer simulations. In this paper, we show how atomic-scale simulations can be used to develop and investigate the properties of glassy surfaces. We illustrate how both first principles calculations and classical molecular mechanics can be used to follow the trajectory at finite temperature of these systems, and obtain statistical thermodynamic averages to compare against available experiments. Both glassy oxide (silica) and non-oxide (chalcogenide) surfaces are considered.

}, isbn = {978-3-319-15674-3}, issn = {0933-033X}, doi = {10.1007/978-3-319-15675-010.1007/978-3-319-15675-0_13}, url = {http://link.springer.com/10.1007/978-3-319-15675-0}, author = {Guido Ori and Carlo Massobrio and Bouzid, A. and Benoit A. Coasne}, editor = {Carlo Massobrio and Du, Jincheng and Bernasconi, Marco and Salmon, Philip S.} } @article {132, title = {Subcontinuum mass transport of condensed hydrocarbons in nanoporous media.}, journal = {Nat Commun}, volume = {6}, year = {2015}, month = {Apr-22-2015}, pages = {Article Number: 6949}, abstract = {

Although hydrocarbon production from unconventional reservoirs, the so-called shale gas, has exploded recently, reliable predictions of resource availability and extraction are missing because conventional tools fail to account for their ultra-low permeability and complexity. Here, we use molecular simulation and statistical mechanics to show that continuum description--Darcy\&$\#$39;s law--fails to predict transport in shales nanoporous matrix (kerogen). The non-Darcy behaviour arises from strong adsorption in kerogen and the breakdown of hydrodynamics at the nanoscale, which contradict the assumption of viscous flow. Despite this complexity, all permeances collapse on a master curve with an unexpected dependence on alkane length. We rationalize this non-hydrodynamic behaviour using a molecular description capturing the scaling of permeance with alkane length and density. These results, which stress the need for a change of paradigm from classical descriptions to nanofluidic transport, have implications for shale gas but more generally for transport in nanoporous media.

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Figure 6

}, issn = {2041-1723}, doi = {10.1038/ncomms7949}, author = {Kerstyn I. Falk and Benoit A. Coasne and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Lyd{\'e}ric Bocquet} } @proceedings {359, title = {Transient regime to fluidized chimney within a granular bed by means of a 2D DEM/LBM modeling}, journal = {IV International Conference on Particle-based Methods (PARTICLES 2015)}, volume = {PARTICLE-BASED METHODS IV-FUNDAMENTALS AND APPLICATIONS}, year = {2015}, month = {sept-30-2015}, pages = {558-566}, publisher = {International Center for Numerical Methods in Engineering (CIMNE)}, address = {SEP 28-30 2015 Barcelona, SPAIN}, abstract = {

Beyond a given threshold, an upward fluid flow at constant flowrate, injected through a small size section, is able to generate a fluidization along a vertical chimney over the entire height of a granular assembly. Fluidization is first initiated in the immediate vicinity of the injection hole and then the fluidized zone grows gradually until reaching the upper surface of the granular packing. In this work, we present numerical results on the kinetics of chimney fluidization in an immersed granular bed produced with two-dimensional simulations coupling the Discrete Element and Lattice Boltzmann Methods (DEM-LBM). A parametric study is carried out with 11 different sets of physical parameters and analyzed based on spatio-temporal diagrams. Then a dimensional analysis allows finding general scaling laws for both threshold and growth rate of the fluidized zone by use of two dimensionless numbers, namely Reynolds and Archimedes numbers, while quite simple empirical relationships can also be proposed.

}, keywords = {DEM, Fluidization, Granular Materials, LBM}, url = {https://hal.archives-ouvertes.fr/hal-01269325}, author = {Jeff Ngoma and Pierre Philippe and St{\'e}phane Bonelli and Cuellar, Pablo and Jean-Yves Delenne and Farhang Radja{\"\i}}, editor = {Onate, E and Bischoff, M and Owen, DRJ} } @article {80, title = {Adsorption of carbon dioxide-methane mixtures in porous carbons: effect of surface chemistry}, journal = {Adsorption-Journal fo the International Adsorption Society}, volume = {20}, year = {2014}, month = {Feb-2014}, pages = {453-463}, type = {Article}, abstract = {

A combined experimental and molecular simulation study of the coadsorption of CO2 and CH4 in porous carbons is reported. We address the effect of surface chemistry by considering a numerical model of disordered porous carbons which has been modified to include heterochemistry (with a chemical composition consistent with that of the experimental sample). We discuss how realistic the numerical sample is by comparing its pore size distribution (PSD), specific surface area, porous volume, and porosity with those for the experimental sample. We also discuss the different criteria used to estimate the latter properties from a geometrical analysis. We demonstrate the ability of the MP method to estimate PSD of porous carbons from nitrogen adsorption isotherms. Both the experimental and simulated coadsorption isotherms resemble those obtained for pure gases (type I in the IUPAC classification). On the other hand, only the porous carbon including the heterogroups allows simulating quantitatively the selectivity of the experimental adsorbent for different carbon dioxide/methane mixtures. This result shows that taking into account the heterochemistry present in porous carbons is crucial to represent correctly adsorption selectivities in such hydrophobic samples. We also show that the adsorbed solution theory describes quantitatively the simulated and experimental coadsorption isotherms without any parameter adjustment.

}, keywords = {Carbon dioxide, Methane, Mixtures, Porous carbons}, issn = {0929-5607}, doi = {10.1007/s10450-013-9570-z}, author = {Pierre Billemont and Benoit A. Coasne and Guy De Weireld} } @article {102, title = {Anomalous composition-dependent dynamics of nanoconfined water in the interlayer of disordered calcium-silicates}, journal = {Journal of Chemical Physics}, volume = {140}, year = {2014}, month = {Feb-07-2014}, pages = {Article Number: 054515}, type = {Article}, abstract = {

With shear interest in nanoporous materials, the ultraconfining interlayer spacing of calcium-silicate-hydrate (C-S-H) provides an excellent medium to study reactivity, structure, and dynamic properties of water. In this paper, we present how substrate composition affects chemo-physical properties of water in ultraconfined hydrophilic media. This is achieved by performing molecular dynamics simulation on a set of 150 realistic models with different compositions of calcium and silicon contents. It is demonstrated that the substrate chemistry directly affects the structural properties of water molecules. The motion of confined water shows a multi-stage dynamics which is characteristic of supercooled liquids and glassy phases. Inhomogeneity in that dynamics is used to differentiate between mobile and immobile water molecules. Furthermore, it is shown that the mobility of water molecules is composition-dependent. Similar to the pressure-driven self-diffusivity anomaly observed in bulk water, we report the first study on composition-driven diffusion anomaly, the self diffusivity increases with increasing confined water density in C-S-H. Such anomalous behavior is explained by the decrease in the typical activation energy required for a water molecule to escape its dynamical cage. (C) 2014 AIP Publishing LLC.

Image of FIG. 1.
Image of FIG. 2.
Image of FIG. 3.
}, issn = {0021-9606}, doi = {10.1063/1.4864118}, author = {Mohammad Javad Abdolhosseini Qomi and Mathieu Bauchy and Franz-Josef Ulm and Roland Jean-Marc Pellenq} } @article {107, title = {An artificial primitive mimic of the Gramicidin-A channel}, journal = {Nature Communications}, volume = {5}, year = {2014}, month = {Jun-26-2014}, type = {Article}, abstract = {

Gramicidin A (gA) is the simplest known natural channel, and important progress in improving conduction activity has previously been obtained with modified natural gAs. However, simple artificial systems mimicking the gA functions are unknown. Here we show that gA can be mimicked using a simple synthetic triazole or {\textquoteleft}T-channel\&$\#$39; forming compound (TCT), having similar constitutional functions as the natural gAs. As in gA channels, the carbonyl moieties of the TCT, which point toward the T-channel core and surround the transport direction, are solvated by water. The net-dipolar alignment of water molecules along the chiral pore surfaces influences the conduction of protons/ions, envisioned to diffuse along dipolar hydrophilic pathways. Theoretical simulations and experimental assays reveal that the conduction through the T-channel, similar to that in gA, presents proton/water conduction, cation/anion selectivity and large open channel-conductance states. T-channels-associating supramolecular chirality with dipolar water alignment-represent an artificial primitive mimic of gA.

Molecular structures and crystal packing.

Molecular simulations of water molecules and ions confined within T-channel.

Bilayer membrane transport experiments.

Single channel conductance of T-channels under {\textquoteleft}early stage{\textquoteright} conductance records.

}, issn = {2041-1723}, doi = {10.1038/ncomms5142}, author = {Barboiu, Mihail and Le Duc, Yann and Gilles, Arnaud and Pierre-Andre Cazade and Michau, Mathieu and Yves-Marie Legrand and Arie Van Der Lee and Benoit A. Coasne and Parvizi, Paria and Post, Joshua and Fyles, Thomas} } @article {84, title = {Atomic-scale modelling of elastic and failure properties of clays}, journal = {Molecular Physics}, volume = {112}, year = {2014}, month = {May-19-2014}, pages = {1294-1305}, type = {Article}, abstract = {

The elastic and failure properties of a typical clay, illite, are investigated using molecular simulation. We employ a reactive (ReaxFF) and a non-reactive (ClayFF) force field to assess the elastic properties of the clay. As far as failure is concerned, ReaxFF was used throughout the study; however, some calculations were also performed with ClayFF. A crack parallel to the clay layers is found to have low fracture resistance when submitted to a tensile loading perpendicular to the crack. The mechanism of both yield and fracture failures is decohesion in the interlayer space. In contrast, under shear loading, the nanoscale failure mechanism is a stick-slip between clay layers. No fracture propagation is observed as the clay layers slide on top of each other. The low fracture resistance in mode I and the stick-slip failure in mode II are both the consequence of the lack of chemical bonds between clay layers where the cohesion is provided by non-covalent interactions. This work, which provides a description of the failure of clays at the microscopic scale, is the first step towards describing the failure of clays at a larger scale where the polycrystalline distribution of clay grains must be taken into account.

}, keywords = {clay, elastic properties, fracture, reactive molecular simulation}, issn = {0026-8976}, doi = {10.1080/00268976.2014.897393}, author = {Gy{\"o}rgy Hantal and Brochard, Laurent and Hadrien Laubie and Ebrahimi, Davoud and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Benoit A. Coasne} } @article {116, title = {Casimir-Polder interaction for gently curved surfaces}, journal = {Physical Review D}, volume = {90}, year = {2014}, month = {Oct-28-2014}, type = {Article}, abstract = {

We use a derivative expansion for gently curved surfaces to compute the leading and the next-to-leading curvature corrections to the Casimir-Polder interaction between a polarizable small particle and a nonplanar surface. While our methods apply to any homogeneous and isotropic surface, explicit results are presented here for perfect conductors. We show that the derivative expansion of the Casimir-Polder potential follows from a resummation of its perturbative series, for small in-plane momenta. We consider the retarded, nonretarded and classical high-temperature limits.

}, issn = {1550-7998}, doi = {10.1103/PhysRevD.90.081702}, author = {Bimonte, Giuseppe and Emig, Thorsten and Kardar, Mehran} } @article {72, title = {Combinatorial molecular optimization of cement hydrates}, journal = {Nat Commun}, volume = {5}, year = {2014}, month = {Sep-24-2014}, pages = {Article Number: 4960}, abstract = {

Despite its ubiquitous presence in the built environment, concrete\â\€$(1s (Bmolecular-level properties are only recently being explored using experimental and simulation studies. Increasing societal concerns about concrete\â\€$(1s (Benvironmental footprint have provided strong motivation to develop new concrete with greater specific stiffness or strength (for structures with less material). Herein, a combinatorial approach is described to optimize properties of cement hydrates. The method entails screening a computationally generated database of atomic structures of calcium-silicate-hydrate, the binding phase of concrete, against a set of three defect attributes: calcium-to-silicon ratio as compositional index and two correlation distances describing medium-range silicon-oxygen and calcium-oxygen environments. Although structural and mechanical properties correlate well with calcium-to-silicon ratio, the cross-correlation between all three defect attributes reveals an indentation modulus-to-hardness ratio extremum, analogous to identifying optimum network connectivity in glass rheology. We also comment on implications of the present findings for a novel route to optimize the nanoscale mechanical properties of cement hydrate.

Figure 1

}, doi = {10.1038/ncomms5960}, author = {Mohammad Javad Abdolhosseini Qomi and Konrad J. Krakowiak and Mathieu Bauchy and Stewart, K.L. and Rouzbeh Shahsavari and Jagannathan, D. and Brommer, D.B. and Alain Baronnet and Markus J Buehler and Sidney Yip and Franz-Josef Ulm and Krystyn J. Van Vliet and Roland Jean-Marc Pellenq} } @article {306, title = {Discussion: Strength-to-fracture scaling in scratching}, journal = {Engineering Fracture Mechanics}, volume = {119}, year = {2014}, month = {Mar-2014}, pages = {21 - 28}, abstract = {

In their paper, Lin and Zhou (2013) add a new dimension to the scratch test analysis, challenging the applicability of Linear Elastic Fracture Mechanics to scratch tests. The question raised is how to integrate the three-dimensionality of scratch tests into the energetic Size Effect Law (SEL) formulated by Ba{\v z}ant for quasi-brittle materials. We show that Lin and Zhou\’s analysis, although relevant is incomplete, as it neglects the blade width, which is critical for the fracture property assessment. In return, if the blade width is properly taken into account, the SEL here proposed is a formidable means to ascertain the fracture toughness from scratching.

Fig. 1. Description of macroscopic scratch tests

Fig. 2. Influence of cutter width w on the intrinsic specific energy ε and the{\textellipsis}

Fig. 3. Strength scaling of scratch tests for different geometries (straight vs

Fig. 4. (a) Presence of a horizontal propagating crack during scratch testing{\textellipsis}

Fig. 5. Application of Ba{\v z}ant{\textquoteright}s Size Effect Law to scratch tests for different{\textellipsis}

}, issn = {00137944}, doi = {10.1016/j.engfracmech.2014.02.025}, author = {Ange-Therese Akono and Franz-Josef Ulm and Zden{\v e}k P Ba{\v z}ant} } @article {89, title = {Effect of Gas Adsorption on Acoustic Wave Propagation in MFI Zeolite Membrane Materials: Experiment and Molecular Simulation}, journal = {Langmuir}, volume = {30}, year = {2014}, month = {Aug-04-2014}, pages = {10336-10343}, type = {Article}, abstract = {
Abstract Image

The present study reports on the development of a characterization method of porous membrane materials which consists of considering their acoustic properties upon gas adsorption. Using acoustic microscopy experiments and atomistic molecular simulations for helium adsorbed in a silicalite-1 zeolite membrane layer, we showed that acoustic wave propagation could be used, in principle, for controlling the membranes operando. Molecular simulations, which were found to fit experimental data, showed that the compressional modulus of the composite system consisting of silicalite-1 with adsorbed He increases linearly with the He adsorbed amount while its shear modulus remains constant in a large range of applied pressures. These results suggest that the longitudinal and Rayleigh wave velocities (VL and VR) depend on the He adsorbed amount whereas the transverse wave velocity VT remains constant.

}, issn = {0743-7463}, doi = {10.1021/la502182k}, author = {Manga, Etoungh D. and Blasco, Hugues and J. Philippe Da-Costa and Drobek, Martin and Ayral, Andre and Le Clezio, Emmanuel and Despaux, Gilles and Benoit A. Coasne and Julbe, Anne} } @proceedings {346, title = {Geomechanics from Micro to MacroInteraction between two localized fluidization cavities in granular media : Experiments and numerical simulation}, journal = {3rd International Symposium on Geomechanics from Micro to Macro}, volume = {Geomechanics from Micro to Macro}, year = {2014}, month = {Sep-2014}, pages = {1571 - 1576}, publisher = {CRC Press}, address = {SEP 01-03-2014 Univ Cambridge, Cambridge, ENGLAND}, abstract = {

In this work, we present experimental and numerical results on the interaction between two localized fluidization cavities in an immersed granular packing. According to the gap between the two locally injected upward fluid flows, each fluidized cavity will evolve independently of the another, or conversely, the two cavities can interact with each other: they merge and eventually behave like a single cavity. Combined optical techniques are used for visualization of particle motion inside the granular media (Refractive Index-Matching between liquid and beads and Planar Laser-Induced Fluorescence), the experimental results are compared to a two-dimensional simulation based on coupled Discrete Element and Lattice Boltzmann Methods (DEM-LBM).

}, isbn = {978-1-138-02707-7}, doi = {10.1201/b17395-286}, author = {Jeff Ngoma and Pierre Philippe and St{\'e}phane Bonelli and Jean-Yves Delenne and Farhang Radja{\"\i}}, editor = {Kenichi Soga and Krishna Kumar and Giovanna Biscontin and Kuo, Matthew} } @proceedings {344, title = {Lattice Boltzmann modeling of liquid clusters in granular media}, journal = {3rd International Symposium on Geomechanics from Micro to Macro}, volume = {Geomechanics from Micro to Macro}, year = {2014}, month = {Dec-03-2014}, pages = {461 - 466}, publisher = {CRC Press}, address = {SEP 01-03-2014 Univ Cambridge, Cambridge, ENGLAND}, abstract = {

We use capillary condensation simulated by a multiphase Lattice Boltzmann model as a means to generate homogeneous distributions of liquid clusters in 2D granular media. Liquid droplets condense from the vapor phase between and on the grains, and they transform into capillary bonds and liquid clusters as thermodynamic equilibrium is approached. As the amount of condensed liquid is increased, liquid clusters of increasing connectivity are formed and the distribution of liquid undergoes topological transitions until the whole pore space is filled by the liquid. We investigate the cluster statistics and local grain environments. From extensive simulations, we also obtain the mean Laplace pressure as a function of the amount of liquid, which is found to be quite similar to the well-known experimental retention curve in soil mechanics.

}, isbn = {978-1-138-02707-7}, doi = {10.1201/b1739510.1201/b17395-83}, author = {Jean-Yves Delenne and Vincent Richefeu and Farhang Radja{\"\i}}, editor = {Kenichi Soga and Krishna Kumar and Giovanna Biscontin and Kuo, Matthew} } @article {109, title = {Magnetic interactions in 3d metal chains on Cu2X/Cu(001) (X = N, O): Comparison with corresponding unsupported chains}, journal = {Physical Review B}, volume = {90}, year = {2014}, month = {Nov-2014}, pages = {195423}, type = {Article}, abstract = {

In this work we present a systematic study of the magnetic interactions within 3d transition-metal chains adsorbed on Cu2N and Cu2O monolayers grown on Cu(001). We are interested in the particular geometric adsorption configuration which gives rise, after relaxation, to the development of diatomic TM-X (X = N, O) chains. By using density functional theory (DFT), we calculate the energy difference between the ferromagnetic and antiferromagnetic intrachain configurations for Ti, V, Cr, Mn, Fe, and Co. Both substrates give rise, with minor differences, to the same magnetic trends, the only chains which are ferromagnetic after adsorption are Cr chains. By performing similar calculations in unsupported chains and introducing a tight-binding-model Hamiltonian based on physically reasonable assumptions we reproduce the magnetic trends obtained from the DFT calculations.

Figure

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Figure

Figure

Figure

}, issn = {1098-0121}, doi = {10.1103/PhysRevB.90.195423}, author = {Urdaniz, M. C. and Barral, M. A. and Llois, A. M. and Andres Sa{\`u}l} } @proceedings {251, title = {Mesoscale simulation of clay aggregate formation and mechanical properties}, journal = {3rd International Symposium on Geomechanics from Micro to Macro}, volume = {Geomechanics from Micro to Macro: Granular Matter}, year = {2014}, month = {Sep-2014}, pages = {539-544}, address = {SEP 01-03 2014 Univ Cambridge, Cambridge, ENGLAND}, abstract = {

This paper proposes a novel methodology for understanding the meso-scale aggregation of clay platelets in water. We use Molecular Dynamics simulations using the CLAYFF force fields to represent the interactions between two layers of Wyoming montmorillonite (Na-smectite) in bulk water. The analyses are used to establish the potential of mean force at different spacings between the layers for edge-to-edge and face-to-face interactions. This is accomplished by finding the change in free energy as a function of the separation distance between the platelets using thermodynamic perturbation theory with a simple overlap sampling method. These nanoscale results are then used to calibrate the Gay\–Berne (GB) potential that represents each platelet as a single-site ellipsoidal body. A coarse-graining upscaling approach then uses the GB potentials and molecular dynamics to represent the meso-scale aggregation of clay platelets (at submicron length scale). Results from meso-scale simulations obtain the equilibrium/jamming configurations for mono-disperse clay platelets. The results show aggregation for a range of clay platelets dimensions and pressures with mean stack size ranging from 3 to 8 platelets. The particle assemblies become more ordered and exhibit more pronounced elastic anisotropy at higher confining pressures. The results are in good agreement with previously measured nano-indentation moduli over a wide range of clay packing densities.

}, issn = {1434-5021}, doi = {10.1007/s10035-016-0655-8}, author = {Ebrahimi, Davoud and Roland Jean-Marc Pellenq and Andrew J. Whittle}, editor = {Kenichi Soga and Krishna Kumar and Giovanna Biscontin} } @proceedings {99, title = {Modelling cement at fundamental scales: From atoms to engineering strength and durability}, journal = {Euro-C Conference}, volume = {COMPUTATIONAL MODELLING OF CONCRETE STRUCTURES, VOL 1}, year = {2014}, month = {2014}, pages = {139-148}, publisher = {CRC Press-Taylor \& Francis Group}, address = {MAR 24-27, 2014, St Anton am Alberg, AUSTRIA}, abstract = {

The mechanics and rheology of cement pastes are largely determined by the Calcium-Silicate-Hydrate (C-S-H) gel, which is normally the main binding phase. The C-S-H gel is an amorphous material with a nanoscale pore network. Here we consider a model structure of the gel, where a continuous molecular model of non-porous C-S-H is combined with a colloidal model that incorporates the porosity of the gel. Numerical simulations predict mechanical properties and microscopic processes associated with yielding under shear. The proposed model can now be used to extract further properties and to contribute to a broader effort aimed at describing and engineering the multi-scale structure and mechanical behaviour of the cement paste. We finally discuss the opportunities offered by our model with respect to the scientific and technological challenges of modelling and controlling ageing and creep over long time scales.

}, isbn = {978-1-138-02641-4; 978-1-315-76203-6}, doi = {10.1201/b16645-16}, author = {Enrico Masoero and Hamlin M. Jennings and Franz-Josef Ulm and Emanuela Del Gado and Hegoi Manzano and Roland Jean-Marc Pellenq and Sidney Yip}, editor = {Bicanic, N and Mang, H and Meschke, G and DeBorst, R} } @proceedings {342, title = {Modelling soft-particle materials}, journal = {3rd International Symposium on Geomechanics from Micro to Macro}, volume = {Geomechanics from Micro to Macro}, year = {2014}, month = {Aug-26-2014}, pages = {43-48}, publisher = {CRC Press}, address = {SEP 01-03-2014 Univ Cambridge, Cambridge, ENGLAND}, abstract = {

Soft-particle materials include colloidal pastes, vesicles, many powders, microgels and suspensions. They share the common feature of being composed of particles that can undergo large deformations without rupture. For the simulation of such materials, we present a modelling approach based on an implicit formulation of the Material Point Method (MPM) interfaced with the Contact Dynamics (CD) method for the treatment of frictional contacts between particles. Each particle is discretized as a collection of material points. The information carried by the material points is projected onto a background mesh, where equations of motion are solved. The mesh solution is then used to update the material points. The implicit formulation of MPM allows for unconditional numerical stability and efficient coupling with implicit treatment of unilateral contacts and friction between the particles by the CD method. We use this model to analyse the compaction process of 2D soft-particle packings. The packing can reach high solid fractions by particle shape change and still flow plastically. The compaction is a nonlinear process in which new contacts are formed between particles and the contact areas increase. We find that the evolution of the packing fraction is a slow logarithmic function of the driving stress as a consequence of increasing contact area. We also evidence the effect of friction, which favours strong stress chains and thus the elongation of particles, leading to a larger packing fraction at a given level of compressive stress as compared to a frictionless particle packing.

}, url = {http://prodinra.inra.fr/record/370208}, author = {Saeid Nezamabadi and Farhang Radja{\"\i} and Julien Averseng}, editor = {Kenichi Soga and Krishna Kumar and Giovanna Biscontin} } @article {650, title = {Molecular dynamics simulation of amorphous HfO 2 for resistive RAM applications}, journal = {Modelling and Simulation in Materials Science and Engineering}, volume = {22}, year = {2014}, month = {Sep-2014}, pages = { Article Number 065006 }, abstract = {

HfO2 is widely investigated as the favoured material for resistive RAM device implementation. The structural features of HfO2 play a fundamental role in the switching mechanisms governing resistive RAM operations, and a comprehensive understanding of the relation between the atomistic properties and final device behaviour is still missing. In addition, despite the fact that ultra-scaled 10 nm resistive RAM will probably be made of amorphous HfO2, a deeper investigation of the structure is necessary. In this paper, the classical molecular dynamics technique was used to investigate the disordered atomic configuration of amorphous HfO2. The influence of density on both the atomistic structure and the diffusion of O species was carefully analysed. The results achieved show that the atomistic structure of an amorphous HfO2 system is strongly affected by the density, and the amorphous system is rearranged in an atomic configuration similar to the crystalline configuration at similar densities. The diffusion of oxygen atoms increases with the decrease of the density, consistent with a less-packed atomic structure which allows for easier movement of this species.

}, issn = {0965-0393}, doi = {10.1088/0965-0393/22/6/065006}, url = {http://stacks.iop.org/0965-0393/22/i=6/a=065006?key=crossref.b7d708e3a43b9124ea539668eee311b0}, author = {Broglia, G and Guido Ori and Larcher, L and Montorsi, M} } @article {70, title = {Multiphase equation of state for carbon addressing high pressures and temperatures}, journal = {Phys Rev. B}, volume = {89}, year = {2014}, month = {Jun-2014}, chapter = {224109}, abstract = {

We present a 5-phase equation of state for elemental carbon which addresses a wide range of density and temperature conditions: 3g/cc\<\ρ\<20g/cc,0K\<T\<\∞. The phases considered are diamond, BC8, simple cubic, simple hexagonal, and the liquid/plasma state. The solid phase free energies are constrained by density functional theory (DFT) calculations. Vibrational contributions to the free energy of each solid phase are treated within the quasiharmonic framework. The liquid free energy model is constrained by fitting to a combination of DFT molecular dynamics performed over the range 10000K\<T\<100000K, and path integral quantum Monte Carlo calculations for T\>100000K (both for \ρ between 3 and 12 g/cc, with select higher- \ρ DFT calculations as well). The liquid free energy model includes an atom-in-jellium approach to account for the effects of ionization due to temperature and pressure in the plasma state, and an ion-thermal model which includes the approach to the ideal gas limit. The precise manner in which the ideal gas limit is reached is greatly constrained by both the highest-temperature DFT data and the path integral data, forcing us to discard an ion-thermal model we had used previously in favor of a new one. Predictions are made for the principal Hugoniot and the room-temperature isotherm, and comparisons are made to recent experimental results.

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}, doi = {10.1103/PhysRevB.89.224109}, author = {L. X. Benedict and K. P. Driver and S. Hamel and B. Militzer and T. Qi and Alfredo A. Correa and Andres Sa{\`u}l and E. Schwegler} } @article {68, title = {Nanofluidics: Bubbles as osmotic membranes}, journal = {Nature nanotechnology}, volume = {9}, year = {2014}, month = {Mar-2014}, pages = {249{\textendash}251}, abstract = {

Nanoscale gas bubbles can act as selective membranes and be used to estimate the condensation coefficient of water.

}, doi = {10.1038/nnano.2014.61}, author = {Lyd{\'e}ric Bocquet} } @article {115, title = {Nanoscale Structure of Cement: Viewpoint of Rigidity Theory}, journal = {Journal of Physical Chemistry C}, volume = {118}, year = {2014}, month = {Jun-12-2014}, pages = {12485-12493}, type = {Article}, abstract = {
Abstract Image

Rigidity theory is a powerful tool to predict the properties of glasses with respect to composition. By reducing such molecular networks to simple mechanical trusses, topological constraint theory filters out all the unnecessary details that ultimately do not affect macroscopic properties. However, the usual constraint enumeration is restricted to networks that are amorphous, homogeneous, and fully connected. On the contrary, calcium\–silicate\–hydrate (C\–S\–H), the binding phase of cement, is partially crystalline and heterogeneous and shows some isolated water molecules. Here, we report how rigidity theory can be used to describe the nanoscale structure of this material by relying on molecular dynamics simulations. The distinction between intact and broken constraints is clearly defined at the atomic scale, thus allowing a precise enumeration of the topological constraints. We show that the rigidity of the C\–S\–H network can be increased by decreasing the Ca/Si molar ratio, which, as predicted by rigidity theory, allows improvement of the hardness of the material. This study suggests that rigidity theory could be applied with great rewards to a broader range of materials than glasses.

}, issn = {1932-7447}, doi = {10.1021/jp502550z}, author = {Mathieu Bauchy and Mohammad Javad Abdolhosseini Qomi and Christophe Bichara and Franz-Josef Ulm and Roland Jean-Marc Pellenq} } @article {262, title = {Order and disorder in calcium{\textendash}silicate{\textendash}hydrate}, journal = {The Journal of Chemical Physics}, volume = {140}, year = {2014}, month = {Jun-07-2014}, pages = {Article Number: 214503}, abstract = {

Despite advances in the characterization and modeling of cement hydrates, the atomic order in Calcium\–Silicate\–Hydrate (C\–S\–H), the binding phase of cement, remains an open question. Indeed, in contrast to the former crystalline model, recent molecular models suggest that the nanoscale structure of C\–S\–H is amorphous. To elucidate this issue, we analyzed the structure of a realistic simulated model of C\–S\–H, and compared the latter to crystalline tobermorite, a natural analogue of C\–S\–H, and to an artificial ideal glass. The results clearly indicate that C\–S\–H appears as amorphous, when averaged on all atoms. However, an analysis of the order around each atomic species reveals that its structure shows an intermediate degree of order, retaining some characteristics of the crystal while acquiring an overall glass-like disorder. Thanks to a detailed quantification of order and disorder, we show that, while C\–S\–H retains some signatures of a tobermorite-like layered structure, hydrated species are completely amorphous.

}, issn = {0021-9606}, doi = {10.1063/1.4878656}, author = {Mathieu Bauchy and Mohammad Javad Abdolhosseini Qomi and Franz-Josef Ulm and Roland Jean-Marc Pellenq} } @article {272, title = {Particle alignment and clustering in sheared granular materials composed of platy particles}, journal = {The European Physical Journal E}, volume = {37}, year = {2014}, month = {Nov-24-2014}, pages = {Article Number: 116}, abstract = {

By means of molecular dynamics simulations, we investigate the texture and local ordering in sheared packings composed of cohesionless platy particles. The morphology of large packings of platy particles in quasistatic equilibrium is complex due to the combined effects of local nematic ordering of the particles and anisotropic orientations of contacts between particles. We find that particle alignment is strongly enhanced by the degree of platyness and leads to the formation of face-connected clusters of exponentially decaying size. Interestingly, due to dynamics in continuous shearing, this ordering phenomenon emerges even in systems composed of particles of very low platyness differing only slightly from spherical shape. The number of clusters is an increasing function of platyness. However, at high platyness the proportion of face-face interactions is too low to allow for their percolation throughout the system.

}, issn = {1292-8941}, doi = {10.1140/epje/i2014-14116-0}, author = {Boton, Mauricio and Estrada, Nicolas and Emilien Az{\'e}ma and Farhang Radja{\"\i}} } @proceedings {348, title = {Pavement infrastructures footprint: The impact of pavement properties on vehicle fuel consumption}, journal = {Euro-C Conference}, volume = {COMPUTATIONAL MODELLING OF CONCRETE STRUCTURES}, year = {2014}, month = {Mar-2014}, pages = {1051-1058}, address = {MAR 24-27 2014 St Anton am Alberg, AUSTRIA}, abstract = {

A novel mechanistic model based on an infinite beam on elastic foundation is developed to
quantify the impact of pavement structural and material properties on pavement deflection and consequently on
vehicle fuel consumption. The model can also account for the effect of temperature and vehicle speed on fuel
consumption. A simplified expression for evaluating the energy dissipation for practical purposes is proposed
and used to investigate the impact of various pavement design systems on fuel consumption. GPS (General Pave-
ment Studies) sections from the FHWA\’s Long Term Pavement Performance program (FHWA 2011) are used
for this study. These sections consist of asphalt concrete (AC), portland cement concrete (PCC) and composite
pavements. The model quantifies the impact of temperature and vehicle speed on the fuel consumption and
confirms that those impacts are negligible for PCC and significant for AC pavements due to their viscoelasticity.

}, url = {https://cshub.mit.edu/sites/default/files/documents/louhghalam-Euro-C-2014.pdf}, author = {Arghavan Louhghalam and Mehdi Akbarian and Franz-Josef Ulm}, editor = {Bicanic, N and Mang, H and Meschke, G} } @article {278, title = {Penetration test in coarse granular material using Contact Dynamics Method}, journal = {Computers and Geotechnics}, volume = {55}, year = {2014}, month = {Jan-2014}, pages = {248 - 253}, abstract = {

Field tests are widely used for soil characterization in geotechnical applications in spite of implementation difficulties. The light penetrometer is a well-known testing tool for fine soils, but the physical interpretation of the output data in the case of coarse granular materials is far less evident. Indeed, the data are considerably more sensitive in this case to various parameters such as fabric structure, particle shapes or the applied impact energy. In order to achieve a better understanding of the penetration process into a coarse granular material, a numerical study was performed by means of contact dynamics simulations. The penetration of a moving tip in a sample composed of irregular grain shapes was studied and the influence of the driving velocity and input energy on the penetration strength was analyzed. The results show that the latter grows with both the penetration rate and energy, despite the strong fluctuations occur due to a jamming\–unjamming process in which the contact network connectivity evolves intermittently in correlation with the penetration strength. This analysis suggests that the time-averaged data provided by a penetrometer is reliable information from which the bulk strength properties of coarse granular materials can be evaluated.

}, issn = {0266352X}, doi = {10.1016/j.compgeo.2013.09.006}, author = {Quezada, Juan Carlos and Breul, Pierre and Saussine, Gilles and Farhang Radja{\"\i}} } @article {73, title = {Physics and technological aspects of nanofluidics}, journal = {Lab on a Chip}, volume = {14}, year = {2014}, month = {Jun-2014}, pages = {3143 - 3158}, abstract = {

From a physical perspective, nanofluidics represents an extremely rich domain. It hosts many mechanisms acting on the nanoscale, which combine together or interact with the confinement to generate new phenomena. Superfast flows in carbon nanotubes, nonlinear electrokinetic transport, slippage over smooth surfaces, nanobubble stability, etc. are the most striking phenomena that have been unveiled over the past few years, and some of them are still awaiting an explanation. One may anticipate that new nanofluidic effects will be discovered in the future, but at the moment, the technological barrier is high. Fabrication of nanochannels is most often a tour de force, slow and costly. However, with the accumulation of technological skills along with the use of new nanofluidic materials (like nanotubes), nanofluidics is becoming increasingly accessible to experimentalists. Among the technological challenges faced by the field, fabricating devices mimicking natural nanometric systems, such as aquaporins, ionic pumps or kidney osmotic filtering, seems the most demanding in terms of groundbreaking ideas. Nanoflow characterization remains delicate, although considerable progress has been achieved over the past years. The targeted application of nanofluidics is not only in the field of genomics and membrane science \– with disruptive developments to be expected for water purification, desalination, and energy harvesting \– but also for oil and gas production from unconventional reservoirs. Today, in view of the markets that are targeted, nanofluidics may well impact the industry more than microfluidics; this would represent an unexpected paradox. These successes rely on using a variety of materials and technologies, using state-of-the-art nanofabrication, or low-tech inexpensive approaches. As a whole, nanofluidics is a fascinating field that is facing considerable challenges today. It possesses a formidable potential and offers much space for creative groundbreaking ideas.

Graphical abstract: Physics and technological aspects of nanofluidics
}, isbn = {1473-0197}, doi = {10.1039/C4LC00325J }, author = {Lyd{\'e}ric Bocquet and Tabeling, Patrick} } @proceedings {100, title = {Poro-chemo-fracture-mechanics ... bottom-up: Application to risk of fracture design of oil and gas cement sheath at early ages}, journal = {Euro-C Conference}, volume = {COMPUTATIONAL MODELLING OF CONCRETE STRUCTURES, VOL 1 }, year = {2014}, month = {Jan-2014}, pages = {61-67}, publisher = {CRC PRESS-TAYLOR \& FRANCIS GROUP}, address = {MAR 24-27, 2014, St Anton am Alberg, AUSTRIA}, abstract = {

With ever more challenging (T, p) environments for cementing applications in oil and gas wells, there is a need to change the classical paradigm of constitutive modeling of the early-age behavior of cementitious materials in oil-and gas well applications. Herein, we propose a bottom-up approach, which starts at the molecular scale of calcium-silicate-hydrates (C-S-H), and propagates this understanding via incremental poroelastic upscaling methods to the meso-and macroscale, and ultimately to the scale of engineering applications. With a clear focus on engineering risk-of-fracture evaluations, we show how to integrate this bottom-up approach with fracture mechanics.

}, isbn = {978-1-138-02641-4; 978-1-315-76203-6}, doi = {10.1201/b16645-8}, author = {Franz-Josef Ulm and Muhannad Abuhaikal and Thomas Alexander Petersen and Roland Jean-Marc Pellenq}, editor = {Bicanic, N and Mang, H and Meschke, G and DeBorst, R} } @article {274, title = {Predicting the settlement of coarse granular materials under vertical loading}, journal = {Scientific Reports}, volume = {4}, year = {2014}, month = {Jul-16-2014}, pages = {Article Number: 5707}, abstract = {

Granular materials are widely used in industrial processes despite their complex and poorly understood mechanical behaviour both in static and dynamic regimes. A prototypical example is the settlement and compaction of a granular bed under vibrational loading. The elementary mechanisms of this process are still unclear and there is presently no established theory or methodology to predict the settlement and its statistical variability. By means of a parametric study, carried out on a full-scale track, and a critical analysis of density relaxation laws, we introduce a novel settlement model in coarse granular materials under cyclic loading. Our extensive experimental data indicate that the settlement process is governed by three independent parameters strongly correlated with the vibration intensity and initial packing fraction. We show that the mean settlement is well predicted by the model with its parameter values extracted from experimental data.

Granular materials are both pressure-dependent and density-dependent materials and exhibit a broad range of intricate behaviours due to their discrete nature, dissipative interactions and generic structural disorder1. The packing fraction may vary as a result of particle rearrangements induced by shearing or vibrations and it leads to dramatic changes in the structure and mechanical response of a granular material2,3,4,5,6,7,8. A long-time logarithmic relaxation law of the packing fraction is systematically observed in experiments9,10. In simple compaction models, this behaviour is attributed to the exponentially increasing time for the particles to reach a new configuration of lower packing fraction. The case of settlement under cyclic loading has, however, been much less investigated. The settlement of granular bed occurs due to both compaction and side-wise spreading. An important industrial example is the railway ballast, which undergoes gradual settlement under the static and dynamic overloads induced by train traffics11,12,13,14. The readjustment of differential settlements requires costly operations on fast-train railways. For this reason, an improved understanding of the parameters governing the settlement process is a critical technological challenge for new developments in this field.

In this paper, we show that the total settlement N under vertical cyclic loading is governed by a logarithmic relaxation law as a function of the number N of cycles:

An external file that holds a picture, illustration, etc. Object name is srep05707-m1.jpg

where the three fitting parameters \∞, B and N0 can be evaluated from the loading parameters, namely the frequency (related to the train speed for ballast) and initial packing fraction of the material. Our experimental correlations between model and loading parameters show consistently that \∞ and B depend on the dimensionless loading intensity \Γ = (A\ω2)/(pd2/m + g), where A is the vibration amplitude, p is the confining pressure (under the sleeper for ballast), d is the average particle diameter, m is the average particle mass and g is gravitational acceleration. We also find that the parameter N0 is linked to the initial packing fraction of the material. In fact, this parameter controls the initial settlement rate, and it was systematically determined by means of a light penetrometer in our experiments on ballast material.

}, doi = {10.1038/srep05707}, author = {Quezada, Juan Carlos and Saussine, Gilles and Breul, Pierre and Farhang Radja{\"\i}} } @article {300, title = {Scratch hardness-strength solutions for cohesive-frictional materials}, journal = {International Journal for Numerical and Analytical Methods in Geomechanics}, volume = {36}, year = {2014}, month = {Feb-25-2014}, pages = {307 - 326}, abstract = {

In this paper we develop analytical solutions for scratch hardness\–strength relations for cohesive-frictional materials of the Mohr\–Coulomb and Drucker\–Prager type. Based on the lower bound yield design approach, closed-form solutions are derived for frictionless scratch devices, and validated against computational upper bound and elastoplastic finite element solutions. The influence of friction at the blade\–material interface is also investigated, for which a simple computational optimization is proposed. Illustrated for scratch tests on cement paste, we show that the proposed solutions provide a convenient way to determine estimates of cohesion and friction parameters from scratch data, and may serve as a benchmark to identify the relevance of strength models for scratch test analysis. Copyright \© 2011 John Wiley \& Sons, Ltd.

}, doi = {10.1002/nag.1008}, author = {Bard, Romain and Franz-Josef Ulm} } @proceedings {345, title = {Shear flow of dense granular suspensions by computer simulations}, journal = {3rd International Symposium on Geomechanics from Micro to Macro}, volume = {Geomechanics from Micro to Macro}, year = {2014}, month = {Apr-2014}, pages = {467-472}, publisher = {CRC Press}, address = {SEP 01-03-2014 Univ Cambridge, Cambridge, ENGLAND}, abstract = {

We analyze the shear flow of dense granular materials composed of circular particles immersed in a viscous fluid by means of Molecular Dynamics simulations interfaced with the Lattice Boltzmann Method. A homogeneous flow of the suspension is obtained through periodic boundary conditions and by directly applying a confining pressure on the granular phase and shearing the fluid phase. The stead-state rheology can be described in terms of effective friction coefficient and packing fraction of the suspension as a function of the ratio of viscous shear stress to confining pressure (frictional description), on one hand, and in terms of normal and shear viscosities of the suspension as a function of the packing fraction (viscous description), on the other hand. We show that the simulation data are consistent with both descriptions and in close agreement with the corresponding scaling laws observed in recent experiments.

}, url = {http://prodinra.inra.fr/record/369542}, author = {L. Amarsid and Patrick Mutabaruka and Jean-Yves Delenne}, editor = {Kenichi Soga and Krishna Kumar and Giovanna Biscontin} } @article {261, title = {A soft matter in construction {\textendash} Statistical physics approach to formation and mechanics of C{\textendash}S{\textendash}H gels in cement}, journal = {The European Physical Journal Special Topics}, volume = {223}, year = {2014}, month = {Oct-2014}, pages = {2285 - 2295}, abstract = {

Calcium-silicate hydrate (C-S-H) is the main binding agent in cement and concrete. It forms at the beginning of cement hydration, it progressively densifies as cement hardens and is ultimately responsible of concrete performances. This hydration product is a cohesive nano-scale gel, whose structure and mechanics are still poorly understood, in spite of its practical importance. Here we review some of the open questions for this fascinating material and a statistical physics approach recently developed, which allows us to investigate the gel formation under the out-of-equilibrium conditions typical of cement hydration and the role of the nano-scale structure in C-S-H mechanics upon hardening. Our approach unveils how some distinctive features of the kinetics of cement hydration can be related to changes in the morphology of the gels and elucidates the role of nano-scale mechanical heterogeneities in the hardened C-S-H.

}, issn = {1951-6355}, doi = {10.1140/epjst/e2014-02264-1}, author = {Emanuela Del Gado and Katerina Ioannidou and Enrico Masoero and Alain Baronnet and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Sidney Yip} } @article {79, title = {Structure-property relationships of water adsorption in metal-organic frameworks}, journal = {New Journal of Chemistry}, volume = {38}, year = {2014}, month = {Apr-16-2014}, pages = {3102-3111}, type = {Article}, abstract = {

A set of 15 metal\–organic frameworks (MIL-53, MIL-68, MIL-125, UiO-66, ZIF) exhibiting different pore size, morphology, and surface chemistry is used to unravel the numerous behaviors of water adsorption at room temperature in this class of materials. Outstanding \“S\”-shaped (type V) adsorption isotherms are observed for MIL-68 type solids. We show that the underlying mechanism of water adsorption can be rationalized using a simple set of three parameters: the Henry constant (i.e. the slope of the adsorption pressure in the low pressure range), the pressure at which pore filling occurs, and the maximum water adsorption capacity. While the Henry constant and pore filling pressure mostly depend on the affinity of water for the surface chemistry and on pore size, respectively, these two parameters are correlated as they both reflect different aspects of the hydrophobicity\–hydrophilicity of the material. For a given type of porous structure, the functionalization of the material by hydrophilic moieties such as hydrogen bonding groups (amine or aldehyde) systematically leads to an increase in the Henry constant concomitantly with a decrease in the pore filling pressure. As for the adsorption mechanism, we show that, for a given temperature, there is a critical diameter (Dc \∼ 20 \Å for water at room temperature) above which pore filling occurs through irreversible capillary condensation accompanied by capillary hysteresis loops. Below this critical diameter, pore filling is continuous and reversible unless the material exhibits some adsorption-induced flexibility.

Graphical abstract: Structure{\textendash}property relationships of water adsorption in metal{\textendash}organic frameworks
}, issn = {1144-0546}, doi = {10.1039/c4nj00076e}, author = {Canivet, Jerome and Bonnefoy, Jonathan and Daniel, Cecile and Legrand, Alexandre and Benoit A. Coasne and David Farrusseng} } @article {67, title = {Sub-additive ionic transport across arrays of solid-state nanopores}, journal = {Physics of Fluids (1994-present)}, volume = {26}, year = {2014}, month = {Jan-31-2014}, pages = {012005}, abstract = {

Nanopores, either biological, solid-state, or ultrathin pierced graphene, are powerful tools which are central to many applications, from sensing of biological molecules to desalination and fabrication of ion selective membranes. However, the interpretation of transport through low aspect-ratio nanopores becomes particularly complex as 3D access effects outside the pores are expected to play a dominant role. Here, we report both experiments and theory showing that, in contrast to na\ïve expectations, long-range mutual interaction across an array of nanopores leads to a non-extensive, sub-linear scaling of the global conductance on the number of pores N. A scaling analysis demonstrates that the N-dependence of the conductance depends on the topology of the network. It scales like G \∼ N/log\ N for a 1D line of pores, and like G\∼\√\‾\‾N for a 2D array, in agreement with experimental measurements. Our results can be extended to alternative transport phenomena obeying Laplace equations, such as diffusive, thermal, or hydrodynamic transport. Consequences of this counter-intuitive behavior are discussed in the context of transport across thin membranes, with applications in energy harvesting.

Image of FIG. 1.
Image of FIG. 2.
Image of FIG. 3.
Image of FIG. 4.
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Image of FIG. 6.
}, doi = {10.1063/1.4863206}, author = {Gadaleta, A and Sempere, C and Simon Gravelle and A. Siria and Fulcrand, R and Christophe Ybert and Lyd{\'e}ric Bocquet} } @article {32, title = {Surface Chemistry and Atomic-Scale Reconstruction of Kerogen-Silica Composites}, journal = {The Journal of Physical Chemistry C}, volume = {118}, year = {2014}, month = {Feb-6-2014}, pages = {2429-2438}, abstract = {
Abstract Image

Interest in gas shale, a novel source rock of natural gas, has increased tremendously in recent years. Better understanding of the kerogen\–rock interaction is of crucial importance for efficient gas extraction and, hence, asset management. In this study, we explore the possible chemical bonds between kerogen and silica, one of the most predominant mineral constituents of gas shale, by means of quantum chemistry. Energetically favorable bond formation reactions are found between alcoholic hydroxyl, carboxylate, and aldehyde groups, as well as aliphatic double bonds of kerogen and the silica surface. The performance of a reactive force field was also assessed in a representative set of chemical reactions and found to be satisfactory. The potential impact of bond formation reactions between the two phases on the actual kerogen\–silica interface is discussed as a function of the kerogen type, maturity, and density. Finally, a methodology aiming to reconstruct realistic kerogen\–silica interfaces is presented.

}, doi = {10.1021/jp406329n}, author = {Gy{\"o}rgy Hantal and Brochard, Laurent and Dias Soeiro Cordeiro, M Natalia and Franz-Josef Ulm and Roland Jean-Marc Pellenq} } @article {86, title = {Surface of glassy GeS2: A model based on a first-principles approach}, journal = {Physical Review B}, volume = {90}, year = {2014}, month = {Jul-2014}, type = {Article}, chapter = {045423}, abstract = {

First-principles calculations within the framework of the density functional theory are used to construct realistic models for the surface of glassy GeS2(g\−GeS2). Both calculations at T=0 K and at finite temperature (T=300 K) are considered. This allows for a comparison between the structural and electronic properties of surface and bulk g\−GeS2. Although the g\−GeS2 surface recovers the main tetrahedral structural motif of bulk g\−GeS2, the number of fourfold coordinated Ge atoms and twofold coordinated S atoms is smaller than in the bulk. On the contrary, the surface system features a larger content of overcoordinated S atoms and threefold coordinated Ge atoms. This effect is more important for the g\−GeS2 surface relaxed at 0 K. Maximally localized Wannier functions (WF) are used to inspect the nature of the chemical bonds of the structural units present at the g\−GeS2 surface. We compare the ability of several charge derivation methods to capture the atomic charge variations induced by a coordination change. Our estimate for the charges allows exploiting the first-principles results as a data base to construct a reliable interatomic force field.

Figure

Figure

Figure

Figure

Figure

Figure

Figure

}, issn = {1098-0121}, doi = {10.1103/PhysRevB.90.045423}, author = {Guido Ori and Carlo Massobrio and Bouzid, A. and Boero, M. and Benoit A. Coasne} } @article {82, title = {Surfactant Behavior of Ionic Liquids Involving a Drug: From Molecular Interactions to Self-Assembly}, journal = {Langmuir}, volume = {30}, year = {2014}, month = {Feb-2014}, pages = {1229-1238}, type = {Article}, abstract = {
Abstract Image

Aggregates formed in an aqueous medium by three ionic liquids CnMImIbu made up of 1-alkyl-3-methyl-imidazolium cation (n = 4, 6, 8) and ibuprofenate anion are investigated. Dynamic light scattering (DLS), cryogenic transmission electron microscopy (cryo-TEM), 1H nuclear magnetic resonance measurements, and atom-scale molecular dynamics simulations are used to shed light on the main interactions governing the formation of the aggregates and their composition. At high concentration, mixed micelles are formed with a composition that depends on the imidazolium alkyl chain length. For the shortest alkyl chain, micelles are mainly composed of ibuprofenate anions with some imidazolium cations intercalated between the anions. Upon increasing the alkyl chain length, the composition of the aggregates gets enriched in imidazolium cations and aggregates of stoichiometric composition are obtained. Attractive interactions between these aggregates led to the formation of larger aggregates. As suggested by molecular simulations, these larger aggregates might constitute the early stage of phase separation. Transitions from micelles to vesicles or ribbons are observed due to dilution effects and changes in the chemical composition of the aggregates. We also show that aggregation can be probed using simple microscopic quantities such as radial distribution functions and average solvation numbers.

}, issn = {0743-7463}, doi = {10.1021/la404166y}, author = {Tourne-Peteilh, Corine and Benoit A. Coasne and In, Martin and Brevet, David and Devoisselle, Jean-Marie and Andre Vioux and Lydie Viau} } @article {74, title = {Ultrahigh interlayer friction in multiwalled boron nitride nanotubes}, journal = {Nat Mater}, volume = {13}, year = {2014}, month = {Jul-2014}, pages = {688 - 693}, abstract = {

Friction at the nanoscale has revealed a wealth of behaviours that depart strongly from the long-standing macroscopic laws of Amontons\–Coulomb1, 2. Here, by using a \‘Christmas cracker\’-type of system in which a multiwalled nanotube is torn apart between a quartz-tuning-fork-based atomic force microscope (TF\–AFM) and a nanomanipulator, we compare the mechanical response of multiwalled carbon nanotubes (CNTs) and multiwalled boron nitride nanotubes (BNNTs) during the fracture and telescopic sliding of the layers. We found that the interlayer friction for insulating BNNTs results in ultrahigh viscous-like dissipation that is proportional to the contact area, whereas for the semimetallic CNTs the sliding friction vanishes within experimental uncertainty. We ascribe this difference to the ionic character of the BN, which allows charge localization. The interlayer viscous friction of BNNTs suggests that BNNT membranes could serve as extremely efficient shock-absorbing\ surfaces.

Multiwalled nanotube Christmas-cracker experimental set-up.

Frequency shift measured by the tuning fork versus the displacement of the piezoscanner during complete tensile load experiments.

}, isbn = {1476-1122}, doi = {10.1038/nmat3985}, author = {Nigues, A. and A. Siria and Vincent, P. and Poncharal, P. and Lyd{\'e}ric Bocquet} } @article {42, title = {Adsorption of carbon dioxide, methane, and their mixtures in porous carbons: effect of surface chemistry, water content, and pore disorder}, journal = {Langmuir}, volume = {29}, year = {2013}, month = {Jan-2013}, pages = {3328{\textendash}3338}, abstract = {
Abstract Image

The adsorption of carbon dioxide, methane, and their mixtures in nanoporous carbons in the presence of water is studied using experiments and molecular simulations. Both the experimental and numerical samples contain polar groups that account for their partially hydrophilicity. For small amounts of adsorbed water, although the shape of the adsorption isotherms remain similar, both the molecular simulations and experiments show a slight decrease in the CO2 and CH4 adsorption amounts. For large amounts of adsorbed water, the experimental data suggest the formation of methane or carbon dioxide clathrates in agreement with previous work. In contrast, the molecular simulations do not account for the formation of such clathrates. Another important difference between the simulated and experimental data concerns the number of water molecules that desorb upon increasing the pressure of carbon dioxide and methane. Although the experimental data indicate that water remains adsorbed upon carbon dioxide and methane adsorption, the molecular simulations suggest that 40 to 75\% of the initial amount of adsorbed water desorbs with carbon dioxide or methane pressure. Such discrepancies show that differences between the simulated and experimental samples are crucial to account for the rich phase behavior of confined water\–gas systems. Our simulations for carbon dioxide\–methane coadsorption in the presence of water suggest that the pore filling is not affected by the presence of water and that adsorbed solution theory can be applied for pressures as high as 15 MPa.

}, doi = {10.1021/la3048938}, author = {Pierre Billemont and Benoit A. Coasne and Guy De Weireld} } @article {218, title = {Environmental scanning electron microscopy (ESEM) and nanoindentation investigation of the crack tip process zone in marble}, journal = {Acta Geotechnica}, volume = {8}, year = {2013}, month = {Jun-2013}, pages = {223 - 245}, abstract = {

This study explores the interaction between crack initiation and nanomechanical properties in the crack-tip fracture process zone of Carrara marble. Specimens with preexisting cracks were loaded in a uniaxial testing machine until the process zone appeared at the tips of the preexisting cracks. ESEM analysis reveals an increase in microcrack density in the process zone with increased loading of the specimen. Nanoindentation testing comprised of lines and grids of single nanoindentations located both near and far from the process zone shows a decrease in both indentation modulus and indentation hardness near grain boundaries in intact material, and with closeness to the process zone. Ultimately, the study confirms that the crack-tip process zone manifests itself as an area of reduced indentation hardness and indentation modulus in marble.

}, issn = {1861-1125}, doi = {10.1007/s11440-013-0213-z}, author = {Brooks, Z. and Franz-Josef Ulm and Einstein, H. H.} } @article {46, title = {ESEM Study of the Humidity-Induced Swelling of Clay Film}, journal = {Langmuir}, volume = {29}, year = {2013}, month = {Oct-02-2013}, pages = {12823{\textendash}12833}, abstract = {
Abstract Image

We measured the humidity-induced swelling of thin self-standing films of montmorillonite clay by a combination of environmental scanning electron microscopy (ESEM) and digital image correlation (DIC). The films were about 40 \μm thick. They were prepared by depositing and evaporating a suspension of clay and peeling off the highly oriented deposits. The rationale for creating such original samples was to obtain mesoscopic samples that could be used to bridge experimentally the gap between the scale of the clay layer and the engineering scale of a macroscopic clay sample. Several montmorillonite samples were used: the reference clay Swy-2, the same clay homoionized with sodium or calcium ions, and a sodium-exchanged Cloisite. The edges of the clay films were observed by ESEM at various relative humidity values between 14\% and 95\%. The ESEM images were then analyzed by DIC to measure the swelling or the shrinkage of the films. We also measured the adsorption/desorption isotherms by weighing the film samples in a humidity-controlled environment. In order to analyze our results, we compared our swelling/shrinkage and adsorption/desorption data with previously published data on the interlayer spacing obtained by X-ray diffraction and with numerical estimates of the interlayer water obtained by molecular dynamics simulation. The swelling and the hysteresis of this swelling were found to be comparable for the overall macroscopic films and for the interlayer space. The same correspondence between film and interlayer space was observed for the amount of adsorbed water. This suggests that, in the range of relative humidities values explored, the films behave like freely swelling oriented stacks of clay layers, without any significant contribution from the mesoporosity. The relevance of this result for the behavior of clayey sedimentary rocks and the differences with the behavior of nonoriented samples (powders or compacted powders) are briefly discussed.

}, doi = {10.1021/la402781p}, author = {Benoit Carrier and Wang, Linlin and Matthieu Vandamme and Roland Jean-Marc Pellenq and Bornert, Michel and Tanguy, Alexandre and Henri Van Damme} } @article {77, title = {First-principles molecular dynamics study of glassy GeS2: Atomic structure and bonding properties}, journal = {Physical Review B}, volume = {88}, year = {2013}, month = {Nov-04-2013}, type = {Article}, abstract = {

The structure of glassy GeS2 is studied in the framework of density functional theory, by using a fully self-consistent first-principles molecular dynamics (FPMD) scheme. A comparative analysis is performed with previous molecular dynamics data obtained within the Harris functional (HFMD) total energy approach. The calculated total neutron structure factor exhibits an unprecedented agreement with the experimental counterpart. In particular, the height of the first sharp diffraction peak (FSDP) improves considerably upon the HFMD results. Both the Ge and the S subnetworks are affected by a consistent number of miscoordinations, coexisting with the main tetrahedral structural motif. Glassy GeS2 features a short-range order quite similar to the one found in glassy GeSe2, a notable exception being the larger number of edge-sharing connections. An electronic structure localization analysis, based on the Wannier functions formalism, provides evidence of a more enhanced ionic character in glassy GeS2 when compared to glassy GeS2.

}, issn = {1098-0121}, doi = {10.1103/PhysRevB.88.174201}, author = {Celino, M. and Le Roux, S. and Guido Ori and Benoit A. Coasne and Bouzid, A. and Boero, M. and Carlo Massobrio} } @proceedings {341, title = {Granular plastic flow and fabric-based internal variables}, journal = {3rd International Symposium on Geomechanics from Micro to Macro}, volume = {Geomechanics from Micro to Macro}, year = {2013}, month = {May-2013}, pages = {3 - 19}, publisher = {CRC Press}, address = {SEP 01-03-2014 Univ Cambridge, Cambridge, ENGLAND}, abstract = {

A microscopic approach to the quasi-static flow of granular materials requires
fabric parameters pertaining to the contact network. We show that the plastic behavior of
granular materials is correctly predicted with the approximation of perfectly rigid particles
interacting via dissipative contacts as simulated by means of the contact dynamics method.
We investigate the correlations between macroscopic variables (internal friction angle and ...

}, isbn = {978-1-138-02707-7}, doi = {10.1201/b1739510.1201/b17395-3}, url = {http://www.crcnetbase.com/doi/book/10.1201/b17395http://www.crcnetbase.com/doi/abs/10.1201/b17395-3}, author = {Farhang Radja{\"\i} and St{\'e}phane Roux}, editor = {Kenichi Soga and Krishna Kumar and Giovanna Biscontin and Kuo, Matthew} } @proceedings {370, title = {GRANULAR SLUMPING IN A FLUID : FOCUS ON RUNOUT DISTANCES}, journal = {3rd International Conference on Particle-based Methods}, volume = {PARTICLE-BASED METHODS III: FUNDAMENTALS AND APPLICATIONS}, year = {2013}, month = {Sept-2013}, pages = {115-123}, address = {SEP 18-20 2013 Stuttgart, GERMANY}, author = {Vincent Topin and Yann Monerie and Perales, F.}, editor = {Bischoff, M and Ramm, E and Onate, E} } @article {284, title = {An interdisciplinary approach towards improved understanding of soil deformation during compaction}, journal = {Soil and Tillage Research}, volume = {128}, year = {2013}, month = {Apr-2013}, pages = {61 - 80}, abstract = {

Soil compaction not only reduces available pore volume in which fluids are stored, but it alters the arrangement of soil constituents and pore geometry, thereby adversely impacting fluid transport and a range of soil ecological functions. Quantitative understanding of stress transmission and deformation processes in arable soils remains limited. Yet such knowledge is essential for better predictions of effects of soil management practices such as agricultural field traffic on soil functioning. Concepts and theory used in agricultural soil mechanics (soil compaction and soil tillage) are often adopted from conventional soil mechanics (e.g. foundation engineering). However, in contrast with standard geotechnical applications, undesired stresses applied by agricultural tyres/tracks are highly dynamic and last for very short times. Moreover, arable soils are typically unsaturated and contain important secondary structures (e.g. aggregates), factors important for affecting their soil mechanical behaviour. Mechanical processes in porous media are not only of concern in soil mechanics, but also in other fields including geophysics and granular material science. Despite similarity of basic mechanical processes, theoretical frameworks often differ and reflect disciplinary focus. We review concepts from different but complementary fields concerned with porous media mechanics and highlight opportunities for synergistic advances in understanding deformation and compaction of arable soils. We highlight the important role of technological advances in non-destructive measurement methods at pore (X-ray tomography) and soil profile (seismic) scales that not only offer new insights into soil architecture and enable visualization of soil deformation, but are becoming instrumental in the development and validation of new soil compaction models. The integration of concepts underlying dynamic processes that modify soil pore spaces and bulk properties will improve the understanding of how soil management affect vital soil mechanical, hydraulic and ecological functions supporting plant growth.

}, issn = {01671987}, doi = {10.1016/j.still.2012.10.004}, author = {Keller, T. and Lamand, M. and Peth, S. and Berli, M. and Jean-Yves Delenne and Baumgarten, W. and Rabbel, W. and Farhang Radja{\"\i} and Rajchenbach, J. and Selvadurai, A.P.S. and Or, D.} } @article {283, title = {Micromechanical analysis of second order work in granular media}, journal = {Granular Matter}, volume = {15}, year = {2013}, month = {Apr-2013}, pages = {221 - 235}, abstract = {

This paper examines instabilities in granular materials from a microscopic point of view through numerical simulations conducted using a discrete element method on two three-dimensional specimens. The detection and the tracking of grain scale deformation mechanisms constitute the key point for a better understanding the failure process and puzzling out what lies behind the vanishing of the macroscopic second order work. For this purpose, the second order work from microscopic variables, involving contact force and branch vector, was introduced and tracked numerically. Then, all contacts depicting negative values of the second order work were deeply investigated, especially their spatial distribution (homogeneity, agglomeration, dispersion\…) within the specimen according to the density of the granular assembly and to the loading direction. A set of comparisons has been considered in this context in order to highlight how a specimen is populated with such contacts whether it is loaded along a direction included within the plastic tensorial zone or along a direction for which the specimen is likely to behave elastically (elastic tensorial zone). Moreover, these comparisons concerned also loading directions within the cone of instability so that links between the vanishing of both microscopic and macroscopic second order works can be established and the local mechanisms responsible for failure occurrence may be figured out.

}, issn = {1434-5021}, doi = {10.1007/s10035-013-0402-3}, author = {Hadda, Nejib and Fran{\c c}ois Nicot and Bourrier, Franck and Sibille, Luc and Farhang Radja{\"\i} and Darve, F{\'e}lix} } @article {76, title = {Molecular intermittent dynamics of interfacial water: probing adsorption and bulk confinement}, journal = {Soft Matter}, volume = {9}, year = {2013}, month = {Jul-26-2013}, pages = {8654-8663}, type = {Article}}, abstract = {

Numerous natural and manufactured systems such as colloidal suspensions, geological pore networks, catalysts, and nanofluidic devices develop a large and sometimes complex interface strongly influencing the dynamics of the fluid entrapped inside these materials. A coarse grain picture of this molecular dynamics can be considered as an intermittence of adsorption steps and bulk relocations from one point to another point of the interface. Adsorption statistics such as the adsorption time distribution and its first moment reflect the degree of interaction of the molecule with the colloidal interface. Relocation statistics strongly depend on the shape of the pore, the surface forces and the bulk confinement. In this paper, a theoretical analysis of this intermittent dynamics is presented. A direct comparison with molecular dynamics simulations is proposed in the case of liquid water confined inside a hydrophilic substrate (silica slit pore with hydroxylated surfaces) or inside a hydrophobic substrate (carbon nanotube). Analysis of this intermittent dynamics allows quantification of the level of interaction of the vicinal water with the solid interface inside an independent adsorption region in exchange with the confined bulk fluid. The possibility of experimentally probing this dynamics using NMR relaxometry is emphasized.

}, issn = {1744-683X}, doi = {10.1039/c3sm51940f}, author = {Pierre E. Levitz and Patrick A Bonnaud and Pierre-Andre Cazade and Roland Jean-Marc Pellenq and Benoit A. Coasne} } @article {45, title = {Molecular simulations of supercritical fluid permeation through disordered microporous carbons}, journal = {Langmuir}, volume = {29}, year = {2013}, month = {Aug-13-2013}, pages = {9985{\textendash}9990}, abstract = {
Abstract Image

Fluid transport through microporous carbon-based materials is inherent in numerous applications, ranging from gas separation by carbon molecular sieves to natural gas production from coal seams and gas shales. The present study investigates the steady-state permeation of supercritical methane in response to a constant cross-membrane pressure drop. We performed dual control volume grand canonical molecular dynamics (DCV-GCMD) simulations to mimic the conditions of actual permeation experiments. To overcome arbitrary assumptions regarding the investigated porous structures, the membranes were modeled after the CS1000a and CS1000 molecular models, which are representative of real microporous carbon materials. When adsorption-induced molecular trapping (AIMT) mechanisms are negligible, we show that the permeability of the microporous material, although not significantly sensitive to the pressure gradient, monotonically decreases with temperature and reservoir pressures, consistent with diffusion theory. However, when AIMT occurs, the permeability increases with temperature in agreement with experimental data found in the literature.

}, doi = {10.1021/la402087r}, author = {Botan, Alexandru and Vermorel, Romain and Franz-Josef Ulm and Roland Jean-Marc Pellenq} } @article {30, title = {Nanofluidic Osmotic Diodes: Theory and Molecular Dynamics Simulations}, journal = {Physical Review Letters}, volume = {111}, year = {2013}, month = {Dec-2013}, pages = {244501}, abstract = {

Osmosis describes the flow of water across semipermeable membranes powered by the chemical free energy extracted from salinity gradients. While osmosis can be expressed in simple terms via the van \’t Hoff ideal gas formula for the osmotic pressure, it is a complex phenomenon taking its roots in the subtle interactions occurring at the scale of the membrane nanopores. Here we use new opportunities offered by nanofluidic systems to create an osmotic diode exhibiting asymmetric water flow under reversal of osmotic driving. We show that a surface charge asymmetry built on a nanochannel surface leads to nonlinear couplings between water flow and the ion dynamics, which are capable of water flow rectification. This phenomenon opens new opportunities for water purification and complex flow control in nanochannels.

Figure

Figure

Figure

Figure

}, doi = {10.1103/PhysRevLett.111.244501}, author = {Picallo, Clara B and Simon Gravelle and Joly, Laurent and Charlaix, Elisabeth and Lyd{\'e}ric Bocquet} } @article {66, title = {Optimizing water permeability through the hourglass shape of aquaporins}, journal = {Proceedings of the National Academy of Sciences}, volume = {110}, year = {2013}, month = {Oct-08-2013}, pages = {16367{\textendash}16372}, abstract = {

The ubiquitous aquaporin channels are able to conduct water across cell membranes, combining the seemingly antagonist functions of a very high selectivity with a remarkable permeability. Whereas molecular details are obvious keys to perform these tasks, the overall efficiency of transport in such nanopores is also strongly limited by viscous dissipation arising at the connection between the nanoconstriction and the nearby bulk reservoirs. In this contribution, we focus on these so-called entrance effects and specifically examine whether the characteristic hourglass shape of aquaporins may arise from a geometrical optimum for such hydrodynamic dissipation. Using a combination of finite-element calculations and analytical modeling, we show that conical entrances with suitable opening angle can indeed provide a large increase of the overall channel permeability. Moreover, the optimal opening angles that maximize the permeability are found to compare well with the angles measured in a large variety of aquaporins. This suggests that the hourglass shape of aquaporins could be the result of a natural selection process toward optimal hydrodynamic transport. Finally, in a biomimetic perspective, these results provide guidelines to design artificial nanopores with optimal performances.

}, doi = {10.1073/pnas.1306447110}, author = {Simon Gravelle and Joly, Laurent and Detcheverry, Fran{\c c}ois and Christophe Ybert and Cottin-Bizonne, C{\'e}cile and Lyd{\'e}ric Bocquet} } @proceedings {360, title = {Penetration strength of coarse granular materials from DEM simulations}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013 }, year = {2013}, month = {Jun-18-2013}, pages = { 241-244}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

Field tests are widely used for soil characterization in geotechnical applications in spite of implementation difficulties. The light penetrometer test is a well-known testing tool for fine soils, but the physical interpretation of the output data in the case of coarse granular materials is far less evident. In fact, the data are considerably more sensitive to various parameters such as fabric structure, particles shape or the applied impact energy. In order to achieve a better understanding of the underlying phenomena, we performed a numerical study by means contact dynamics DEM simulations. We consider the penetration of a moving tip into a sample composed of irregular grain shapes and we analyze the influence of the driving velocity and applied energy on the penetration strength. We find that the latter grows with both the penetration rate and energy. Force fluctuations on the tip involve a jamming-unjamming process. The typology of contact network and inter-granular friction play a major role in the fluctuations and measured values of the cone penetration strength.

}, doi = {10.1063/1.4811912}, author = {Quezada, Juan Carlos and Saussine, Gilles and Breul, Pierre and Farhang Radja{\"\i}}, editor = {Yu, A and Dong, K and Yang, R} } @article {285, title = {Quasistatic rheology and microstructural description of sheared granular materials composed of platy particles}, journal = {Physical Review E}, volume = {87}, year = {2013}, month = {Mar-28-2013}, pages = {Article Number: 032206}, abstract = {

This is the first paper of a series devoted to the micro-mechanical modeling of clayey soils, by means of discrete element simulations. We specifically focus here on the effect of the platy shape of particles by reducing the interactions between particles to mechanical contact forces (i.e., neither electrostatic repulsion nor van der Waals forces are taken into account). The particles are three-dimensional square plates, approximated as spheropolyhedra. Several samples composed of particles of different levels of platyness (related to the ratio of length to thickness) were numerically prepared and sheared up to large deformations. We analyzed the shear strength, packing fraction, orientation of the particles, connectivity, fabric of the interactions network, and interaction forces as functions of the platyness. We find that both the mechanical behavior and microstructure are strongly dependent on the degree of platyness. The principal underlying phenomenon is the alignment of particle faces along a particular direction. This ordering phenomenon, which emerges even for shapes that deviate only slightly from that of a sphere, enhances the ability of the packing to develop an anisotropic structure leading to large shear strength, especially as a consequence of the fabric and mobilization of friction forces. Moreover, the connectivity of the packings and their packing fraction also evolve with the platyness. In particular, the packing fraction evolves in a nonmonotonic fashion, as observed in other granular materials composed of elongated or angular particles.

}, issn = {1539-3755}, doi = {10.1103/PhysRevE.87.032206}, author = {Boton, Mauricio and Emilien Az{\'e}ma and Estrada, Nicolas and Farhang Radja{\"\i} and Lizcano, Arcesio} } @proceedings {361, title = {Settlement statistics of a granular layer composed of polyhedral particles}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {Jun-18-2013}, pages = {333-336}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

We use 3D contact dynamics simulations to investigate the mechanical equilibrium and settlement of a granular material composed of irregular polyhedral particles confined between two horizontal frictional planes. We show that, as a consequence of mobilized wall-particle friction force at the top and bottom boundaries, the transient deformation induced by a constant vertical load increment is controlled by the aspect ratio (thickness over width) of the packing as well as the stress ratio. The transient deformation declines considerably for increasingly smaller aspect ratios and grows with the stress ratio. From the simulation data for a large number of independent configurations, we find that sample-to-sample fluctuations of the deformation have a broad distribution and they scale with the average deformation.

}, doi = {10.1063/1.4811935}, author = {Quezada, Juan Carlos and Saussine, Gilles and Breul, Pierre and Farhang Radja{\"\i}}, editor = {Yu, A and Dong, K and Yang, R} } @proceedings {363, title = {Shear strength and microstructure of 3D assemblies of platy particles}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {Jul-09-2013}, pages = {519-522}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

As a first step towards particle-scale modeling of clayey soils, we investigate the mechanical behavior and microstructure of assemblies of three-dimensional rectangular platy particles by means of the discrete element method. Several samples composed of particles of different levels of platyness (ratio of width to thickness) were numerically prepared and sheared to large deformations. We analyze the shear strength, packing fraction, connectivity, contact and force anisotropies, and mobilization of friction forces as functions of platyness.We find that both the mechanical behavior and microstructure are strongly dependent on the degree of platyness. This happens, in particular, because of the alignment of particle faces along a particular direction. Additionally, as observed for other granular materials with complex shapes, the packing fraction passes by a peak value before decreasing for larger values of platyness.

}, keywords = {Clays, DEM, Microstructure, Shear strength}, url = {https://hal.archives-ouvertes.fr/hal-00842787}, author = {Boton, Mauricio and Emilien Az{\'e}ma and Estrada, Nicolas and Farhang Radja{\"\i} and Lizcano, Arcesio}, editor = {Yu, A and Dong, K and Yang, R} } @conference {36, title = {Water Isotherms, Shrinkage and Creep of Cement Paste: Hypotheses, Models and Experiments}, booktitle = {Mechanics and Physics of Creep, Shrinkage, and Durability of Concrete: A Tribute to Zdenek P. Ba{\.z}ant}, year = {2013}, month = {Sep-25-2013}, publisher = {ASCE Publications}, organization = {ASCE Publications}, abstract = {

Cement paste has a complex mesoscale structure, and small changes in its pore network potentially cause large variation in measurements such as the water isotherm (also nitrogen). We deconvolute the water isotherm with the help of advanced computational techniques, hypotheses, and a re-examination of published data. The pore system is divided into four different categories, each containing water with its own physical properties. By viewing the highly interdependent roles of water in each of the pore categories as a system, new insights are gained regarding possible mechanisms that control drying, shrinkage, and creep, and experimental strategies for verification.

}, doi = {10.1061/9780784413111.015}, author = {Hamlin M. Jennings and Enrico Masoero and Pinson, Matthew B and Strekalova, Elena G and Patrick A Bonnaud and Hegoi Manzano and Qing Ji and Jeffrey J. Thomas and Roland Jean-Marc Pellenq and Franz-Josef Ulm and others} } @article {51, title = {Hydration of calcium oxide surface predicted by reactive force field molecular dynamics}, journal = {Langmuir}, volume = {28}, year = {2012}, month = {Mar-06-2012}, pages = {4187{\textendash}4197}, abstract = {
Abstract Image

In this work, we present the parametrization of Ca\–O/H interactions within the reactive force field ReaxFF, and its application to study the hydration of calcium oxide surface. The force field has been fitted using density functional theory calculations on gas phase calcium\–water clusters, calcium oxide bulk and surface properties, calcium hydroxide, bcc and fcc Ca, and proton transfer reactions in the presence of calcium. Then, the reactive force field has been used to study the hydration of the calcium oxide {001} surface with different water contents. Calcium oxide is used as a catalyzer in many applications such as CO2 sequestration and biodiesel production, and the degree of surface hydroxylation is a key factor in its catalytic performance. The results show that the water dissociates very fast on CaO {001} bare surfaces without any defect or vacancy. The surface structure is maintained up to a certain amount of water, after which the surface undergoes a structural rearrangement, becoming a disordered calcium hydroxyl layer. This transformation is the most probable reason for the CaO catalytic activity decrease.

}, doi = {10.1021/la204338m}, author = {Hegoi Manzano and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Markus J Buehler and Adri CT Van Duin} } @proceedings {354, title = {Microscopic Origins of Shear Strength in Packings Composed of Elongated Particles}, journal = {9th International Workshop on Bifurcation and Degradation in Geomaterials (IWBDG 2011)}, volume = {Springer Series in Geomechanics and Geoengineering - ADVANCES IN BIFURCATION AND DEGRADATION IN GEOMATERIALS}, year = {2012}, month = {Apr-11-2012}, pages = {21-27}, address = {MAY 23-26 2011 Porquerolles, FRANCE}, abstract = {

We investigate the rheology, force transmission and texture of granular materials composed of elongated particles by means of contact dynamics simulations. The particles have a rounded-cap rectangular (RCR) shape described by a single elongation parameter varying from 0 for a circular particle to 1 for an infinitely thin or long particle. We study the quasi-static behavior, structural and force anisotropies as a function of the elongation parameter for packings submitted to biaxial compression. The shear strength is found to increase linearly with this parameter whereas the solid fraction both at the initial isotropic state and in the critical state is nonmonotonous. We show that for these elongated particles a harmonic decomposition of the stress tensor provides a fairly good approximation of the internal state. Our data suggest that the increase of shear strength with reflects both enhanced friction mobilization and anisotropic particle orientation as the elongation of the particles increases.

}, keywords = {Elongated particles, Fabric properties, force transmission, Harmonic decomposition}, url = {https://hal.archives-ouvertes.fr/hal-00686728}, author = {Emilien Az{\'e}ma and Farhang Radja{\"\i}}, editor = {St{\'e}phane Bonelli and Dascalu, Cristian and Fran{\c c}ois Nicot} } @article {56, title = {Poromechanics of microporous media}, journal = {Journal of the Mechanics and Physics of Solids}, volume = {60}, year = {2012}, month = {Apr-2012}, pages = {606{\textendash}622}, abstract = {

Microporous media, i.e., porous media made of pores with a nanometer size, are important for a variety of applications, for instance for sequestration of carbon dioxide in coal, or for storage of hydrogen in metal-organic frameworks. In a pore of nanometer size, fluid molecules are not in their bulk state anymore since they interact with the atoms of the solid: they are said to be in an adsorbed state. For such microporous media, conventional poromechanics breaks down.

In this work we derive poroelastic constitutive equations which are valid for a generic porous medium, i.e., even for a porous medium with pores of nanometer size. The complete determination of the poromechanical behavior of a microporous medium requires knowing how the amount of fluid adsorbed depends on both the fluid bulk pressure and the strain of the medium. The derived constitutive equations are validated with the help of molecular simulations on one-dimensional microporous media. Even when a microporous medium behaves linearly in the absence of any fluid (i.e., its bulk modulus does not depend on strain), we show that fluid adsorption can induce non-linear behavior (i.e., its drained bulk modulus can then depend significantly on strain). We also show that adsorption can lead to an apparent Biot coefficient of the microporous medium greater than unity or smaller than zero.

The poromechanical response of a microporous medium to adsorption significantly depends on the pore size distribution. Indeed, the commensurability (i.e., the ratio of the size of the pores to that of the fluid molecules) proves to play a major role. For a one-dimensional model of micropores with a variety of pore sizes, molecular simulations show that the amount of adsorbed fluid depends linearly on the strain of the medium. We derive linearized constitutive equations which are valid when such a linear dependence of the adsorbed amount of fluid on the strain is observed.

As an application, the case of methane and coal is considered. Molecular simulations of an adsorption of methane on a microporous realistic model for coal are performed with a flexible solid skeleton. The applicability of the set of linearized constitutive equations to this case is discussed and the results are shown to be consistent with swelling data measured during a classical adsorption experiment.

Example of molecular configuration. The fluid molecules can enter or leave the ...

Amount of fluid molecules adsorbed per unit length of the undeformed chain, in ...

Apparent tangent drained bulk modulus Kt of the crystalline chain.

}, doi = {10.1016/j.jmps.2012.01.001}, author = {Brochard, Laurent and Matthieu Vandamme and Roland Jean-Marc Pellenq} } @article {53, title = {Set in stone? A perspective on the concrete sustainability challenge}, journal = {MRS bulletin}, volume = {37}, year = {2012}, month = {Apr-09-2012}, pages = {395{\textendash}402}, abstract = {

As the most abundant engineered material on Earth, concrete is essential to the physical infrastructure of all modern societies. There are no known materials that can replace concrete in terms of cost and availability. There are, however, environmental concerns, including the significant CO2 emissions associated with cement production, which create new incentives for university\–industry collaboration to address concrete sustainability. Herein, we examine one aspect of this challenge\—the translation of scientific understanding at the microscale into industrial innovation at the macroscale\—by seeking improvements in cement-paste processing, performance, and sustainability through control of the mechanisms that govern microstructure development. Specifically, we consider modeling, simulation, and experimental advances in fracture, dissolution, precipitation, and hydration of cement paste precursors, as well as properties of the hardened cement paste within concrete. The aim of such studies is to optimize the chemical reactivity, mechanical performance, and other physical properties of cement paste to enable more sustainable processing routes for this ubiquitous material.

}, doi = {10.1557/mrs.2012.55}, author = {Krystyn J. Van Vliet and Roland Jean-Marc Pellenq and Markus J Buehler and Jeffrey C Grossman and Hamlin M. Jennings and Franz-Josef Ulm and Sidney Yip} } @article {49, title = {Solvated calcium ions in charged silica nanopores}, journal = {The Journal of Chemical Physics}, volume = {137}, year = {2012}, month = {Aug-14-2012}, pages = {Article Number: 064706}, abstract = {

Hydroxyl surface density in porous silica drops down to nearly zero when the pH of the confined aqueous solution is greater than 10.5. To study such extreme conditions, we developed a model of slit silicananopores where all the hydrogen atoms of the hydroxylated surface are removed and the negative charge of the resulting oxygen dangling bonds is compensated by Ca2+ counterions. We employed grand canonical Monte Carlo and molecular dynamics simulations to address how the Ca2+ counterions affect the thermodynamics, structure, and dynamics of confined water. While most of the Ca2+ counterions arrange themselves according to the so-called \“Stern layer,\” no diffuse layer is observed. The presence of Ca2+ counterions affects the pore filling for strong confinement where the surfaceeffects are large. At full loading, no significant changes are observed in the layering of the first two adsorbed water layers compared to nanopores with fully hydroxylated surfaces. However, the water structure and water orientational ordering with respect to the surface is much more disturbed. Due to the super hydrophilicity of the Ca2+-silica nanopores,waterdynamics is slowed down and vicinal water molecules stick to the pore surface over longer times than in the case of hydroxylated silicasurfaces. These findings, which suggest the breakdown of the linear Poisson\–Boltzmann theory, provide important information about the properties of nanoconfined electrolytes upon extreme conditions where the surface charge and ion concentration are large.

Image of FIG. 1.

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Image of FIG. 6.

}, doi = {10.1063/1.4742854}, author = {Patrick A Bonnaud and Benoit A. Coasne and Roland Jean-Marc Pellenq} } @article {297, title = {Stability, deformation, and variability of granular fills composed of polyhedral particles}, journal = {Physical Review E}, volume = {86}, year = {2012}, month = {Sep-28-2012}, pages = {Article Number: 031308 Part: 1}, abstract = {

By means of extensive contact dynamics simulations, we investigate the mechanical equilibrium and deformation of a granular material composed of irregular polyhedral particles confined between two horizontal frictional planes. We show that, as a consequence of mobilized wall-particle friction forces at the top and bottom boundaries, the transient deformation induced by a constant vertical load is controlled by the aspect ratio (thickness over width) of the packing as well as the stress ratio. The transient deformation declines considerably for increasingly smaller aspect ratios and grows with the stress ratio. From the simulation data for a large number of independent configurations, we find that sample-to-sample fluctuations of the deformation have a broad distribution and they scale with the average deformation. We also analyze the evolution of particle connectivity during settlement and with the applied force. The face-face and edge-face contacts between polyhedral particles concentrate strong force chains with a growing proportion as a function of the applied force.

}, issn = {1539-3755}, doi = {10.1103/PhysRevE.86.031308}, author = {Quezada, Juan Carlos and Breul, Pierre and Saussine, Gilles and Farhang Radja{\"\i}} } @article {58, title = {Structure and properties of nanoscale materials: theory and atomistic computer simulation}, journal = {International Journal of Nanotechnology}, volume = {9}, year = {2012}, month = {2012}, pages = {576{\textendash}604}, abstract = {

We present a review of a few research topics developed within the \"Theory and Atomistic Computer Simulation\" Department at CINaM. The bottom line of the scientific activity is to use up\–to\–date theoretical and computer simulation techniques to address physics and materials science problems, often at the nanometric scale, in close contact with experimental groups. It ranges from the study of the structure and properties of molecular systems for organic electronics to metallic clusters and alloys, magnetic oxides, nuclear fuels and carbon\–based nanostructures. These studies are motivated by fundamental research questions as well as more applied goals including environmental and energy issues, or information technologies. This broad spectrum of activities requires a large range of techniques, from theory and ab initio calculations to semi\–empirical models incorporated in Monte Carlo or molecular dynamics simulations.

}, doi = {10.1504/IJNT.2012.045335 }, author = {Christophe Bichara and Marsal, P and Mottet, C and Roland Jean-Marc Pellenq and F. Ribeiro and Andres Sa{\`u}l and G. Tr{\'e}glia and Weissker, H{\textendash}Ch} } @article {93, title = {Thermodynamics of Water Confined in Porous Calcium-Silicate-Hydrates}, journal = {Langmuir}, volume = {28}, year = {2012}, month = {Aug-07-2012}, pages = {11422-11432}, type = {Article}, abstract = {
Abstract Image

Water within pores of cementitious materials plays a crucial role in the damage processes of cement pastes, particularly in the binding material comprising calcium-silicate-hydrates (C\–S\–H). Here, we employed Grand Canonical Monte Carlo simulations to investigate the properties of water confined at ambient temperature within and between C\–S\–H nanoparticles or \“grains\” as a function of the relative humidity (\%RH). We address the effect of water on the cohesion of cement pastes by computing fluid internal pressures within and between grains as a function of \%RH and intergranular separation distance, from 1 to 10 \Å. We found that, within a C\–S\–H grain and between C\–S\–H grains, pores are completely filled with water for \%RH larger than 20\%. While the cohesion of the cement paste is mainly driven by the calcium ions in the C\–S\–H, water facilitates a disjoining behavior inside a C\–S\–H grain. Between C\–S\–H grains, confined water diminishes or enhances the cohesion of the material depending on the intergranular distance. At very low \%RH, the loss of water increases the cohesion within a C\–S\–H grain and reduces the cohesion between C\–S\–H grains. These findings provide insights into the behavior of C\–S\–H in dry or high-temperature environments, with a loss of cohesion between C\–S\–H grains due to the loss of water content. Such quantification provides the necessary baseline to understand cement paste damaging upon extreme thermal, mechanical, and salt-rich environments.

}, issn = {0743-7463}, doi = {10.1021/la301738p}, author = {Patrick A Bonnaud and Qing Ji and Benoit A. Coasne and Roland Jean-Marc Pellenq and Krystyn J. Van Vliet} } @article {59, title = {Adsorption-induced deformation of microporous materials: coal swelling induced by co2{\textendash}ch4 competitive adsorption}, journal = {Langmuir}, volume = {28}, year = {2011}, month = {Dec-20-2011}, pages = {2659{\textendash}2670}, abstract = {
Abstract Image

Carbon dioxide injection in coal seams is known to improve the methane production of the coal seam, while ensuring a safe and long-term carbon sequestration. This improvement is due to the preferential adsorption of CO2 in coal with respect to CH4: an injection of CO2 thus results in a desorption of CH4. However, this preferential adsorption is also known to cause a differential swelling of coal, which results in a significant decrease in the reservoir permeability during the injection process. Recent studies have shown that adsorption in coal micropores (few angstr\öms in size) is the main cause of the swelling. In this work, we focus on the competitive adsorption behavior of CO2 and CH4 in micropores. We perform molecular simulations of adsorption with a realistic atomistic model for coal. The competitive adsorption is studied at various temperatures and pressures representative of those in geological reservoirs. With the help of a poromechanical model, we then quantify the subsequent differential swelling induced by the computed adsorption behaviors. The differential swelling is almost insensitive to the geological temperatures and pressures considered here and is proportional to the CO2 mole fraction in the coal.

}, doi = {10.1021/la204072d}, author = {Brochard, Laurent and Matthieu Vandamme and Roland Jean-Marc Pellenq and Fen-Chong, Teddy} } @proceedings {349, title = {Creep behaviour of confined layers of polyhedral grains}, journal = {2nd International Conference on Particle-Based Methods - Fundamentals and Applications (Particles)}, volume = {PARTICLE-BASED METHODS II: FUNDAMENTALS AND APPLICATIONS }, year = {2011}, month = {Oct-2011}, pages = {574-583}, address = {OCT 26-28 2011 Barcelona, SPAIN}, abstract = {

By means of contact dynamics simulations, we investigate the creep deformation of a thin granular layer composed of irregular polyhedral particles under the action of a constant vertical overload applied on a horizontal wall on top of the layer. We show that the total deformation induced by the overload increases with the ratio between the vertical and confining horizontal stresses and the aspect ratio of the sample. The effect of the aspect ratio is a consequence of the mobilized wall-grain friction forces at the top and bottom boundaries, that lead to enhanced strength by stabilizing strong force chains at the center of the sample. We also evidence the influence of loading history due to strain-induced fabric change or inertial effects resulting from the instant application of the overload. The topology of the contact network evolves in close correlation with creep. In particular, the face/face contacts between polyhedral particles concentrate largest force chains and their number is an increasing function of creep. A crucial feature of a confined granular system is the statistical variability of the mechanical response that we analyzed for creep deformations by performing a large number of simulations for independent initial configurations. Our data indicate that the distribution of fluctuations with respect to the mean creep falls off exponentially.

}, url = {https://hal.archives-ouvertes.fr/hal-00761094}, author = {Quezada, Juan Carlos and Farhang Radja{\"\i} and Breul, Pierre and Saussine, Gilles}, editor = {Onate, E and Owen, DRJ} } @proceedings {352, title = {Modeling Porous Granular Aggregates}, journal = {9th International Workshop on Buifurcation and Degradation in Geomaterials (IWBDG 2011)}, volume = {Springer Series in Geomechanics and Geoengineering - ADVANCES IN BIFURCATION AND DEGRADATION IN GEOMATERIALS}, year = {2011}, month = {May-28-2011}, pages = {249 - 254}, publisher = {Springer Netherlands}, address = {MAY 23-26 2011 Porquerolles, FRANCE}, abstract = {

We rely on 3D simulations based on the Lattice Element Method (LEM) to analyze the failure of porous granular aggregates under tensile loading. We investigate crack growth by considering the number of broken bonds in the particle phase as a function of the matrix volume fraction and particle-matrix adhesion. Three regimes are evidenced, corresponding to no particle damage, particle abrasion and particle fragmentation, respectively. We also show that the probability density of strong stresses falls off exponentially at high particle volume fractions where a percolating network of jammed particles occurs. Decreasing the matrix volume fraction leads to increasingly broader stress distribution and hence a higher stress concentration. Our findings are in agreement with 2D results previously reported in the literature.

}, isbn = {978-94-007-1420-5}, issn = {1866-8755}, doi = {10.1007/978-94-007-1421-2_32}, author = {Rafik Aff{\`e}s and Vincent Topin and Jean-Yves Delenne and Yann Monerie}, editor = {St{\'e}phane Bonelli and Dascalu, Cristian and Fran{\c c}ois Nicot} } @article {258, title = {The nanogranular origin of friction and cohesion in shale-A strength homogenization approach to interpretation of nanoindentation results}, journal = {International Journal for Numerical and Analytical Methods in Geomechanics}, volume = {35}, year = {2011}, month = {Dec-10-2011}, pages = {1854 - 1876}, abstract = {

An inverse micromechanics approach allows interpretation of nanoindentation results to deliver cohesive-frictional strength behavior of the porous clay binder phase in shale. A recently developed strength homogenization model, using the Linear Comparison Composite approach, considers porous clay as a granular material with a cohesive-frictional solid phase. This strength homogenization model is employed in a Limit Analysis Solver to study indentation hardness responses and develop scaling relationships for indentation hardness with clay packing density. Using an inverse approach for nanoindentation on a variety of shale materials gives estimates of packing density distributions within each shale and demonstrates that there exists shale-independent scaling relations of the cohesion and of the friction coefficient that vary with clay packing density. It is observed that the friction coefficient, which may be interpreted as a degree of pressure-sensitivity in strength, tends to zero as clay packing density increases to one. In contrast, cohesion reaches its highest value as clay packing density increases to one. The physical origins of these phenomena are discussed, and related to fractal packing of these nanogranular materials. Copyright \© 2010 John Wiley \& Sons, Ltd.

}, doi = {10.1002/nag.v35.1710.1002/nag.984}, author = {Bobko, Christopher P. and Gathier, Benjamin and J. Alberto Ortega and Franz-Josef Ulm and Borges, Lavinia and Younane N. Abousleiman} } @proceedings {353, title = {Onset of Immersed Granular Avalanches by DEM-LBM Approach}, journal = {9th International Workshop on Buifurcation and Degradation in Geomaterials (IWBDG 2011)}, volume = {Springer Series in Geomechanics and Geoengineering - ADVANCES IN BIFURCATION AND DEGRADATION IN GEOMATERIALS}, year = {2011}, month = {May-28-2011}, pages = {109 - 115}, publisher = {Springer Netherlands}, address = {MAY 23-26 2011 Porquerolles, FRANCE}, abstract = {

We present 3D grain-fluid simulations based on the discrete element method interfaced with the lattice Boltzmann method and applied to investigate the initiation of underwater granular flows. We prepare granular beds of 800 spherical grains with different values of the initial solid fraction in a biperiodic rectangular box. In order to trigger an avalanche, the bed is instantaneously tilted to a finite slope angle above the maximum angle of stability. We simulate the dynamics of the transient flow for different solid fractions. In agreement with the experimental work of Iverson (Water Resour Res 36(7):1897\–1910, 2000) and Pailha et\ al. (Phys Fluids 20(11):111701, 2008), we find that the flow onset is controlled by the initial solid fraction.

}, isbn = {978-94-007-1420-5}, issn = {1866-8755}, doi = {10.1007/978-94-007-1421-210.1007/978-94-007-1421-2_14}, author = {Jean-Yves Delenne and Mansouri, M. and Farhang Radja{\"\i} and Moulay Sa{\"\i}d El Youssoufi and Seridi, A.}, editor = {St{\'e}phane Bonelli and Dascalu, Cristian and Fran{\c c}ois Nicot} } @proceedings {364, title = {Springer Series in Geomechanics and Geoengineering Multiscale and Multiphysics Processes in Geomechanics SIMULATION OF HYDRATION AND ELASTIC PROPERTIES OF MONTMORILLONITE USING MOLECULAR DYNAMICS}, journal = {International Workshop on Multiscale and Multiphysics Processes in Geomechanics}, volume = {Springer Series in Geomechanics and Geoengineering}, year = {2011}, month = {2011}, pages = {105 - 108}, publisher = {Springer Berlin Heidelberg}, address = {JUN 23-25 2010 Stanford Univ, Stanford, CA}, abstract = {

This article describes molecular-level simulations of the adsorption isotherm and elastic properties for a Wyoming Na-montmorillonite using the General Utility Lattice Program. The selected clay mineral includes isomorphous substitutions in both the silica tetrahedral and octahedral gibbsite sheets. The resulting negative charges are balanced by Na+ cations. The authors have investigated the importance of different interatomic potentials in understanding the adsorption of water molecules (at ambient temperature, 300K). A unique combination of NPT and Grand Canonical ensemble simulations using Core\–Shell potential shows intra-layer adsorption, while the same approach based on empirical CLAYFF potential produces only interlayer water adsorption. There is a correspondingly large difference in the theoretical elastic modulus normal to the clay sheets using the two different sets of force potentials. This article discusses the underlying reasons for these differences and reviews the experimental evidence supporting intra-layer water absorption in montmorillonite.

}, isbn = {978-3-642-19629-4}, issn = {1866-8755}, doi = {10.1007/978-3-642-19630-0_27}, author = {Roland Jean-Marc Pellenq and Andrew J. Whittle and Ebrahimi, Davoud}, editor = {Borja, Ronaldo I. and Wu, Wei} } @proceedings {347, title = {STRENGTH HOMOGENIZATION FOR COHESIVE-FRICTIONAL COMPOSITES: A LINEAR COMPARISON COMPOSITE APPROACH}, journal = {International Workshop on Multiscale and Multiphysics Processes in Geomechanics}, volume = {Springer Series in Geomechanics and Geoengineering}, year = {2011}, month = {Jan-2011}, pages = {57 - 60}, publisher = {Springer Berlin Heidelberg}, address = {JUN 23-25 2010 Stanford Univ, Stanford, CA}, abstract = {

In this work, we address the homogenization of cohesive-frictional strength properties of composite materials through the application of the Linear Comparison Composite (LCC) theory. The LCC methodology is implemented in a multiscale strength model relevant to geomaterials with heterogeneities associated with pore spaces and rigid-like grains. The proposed micromechanics solutions offer quantitative assessments of the effects of grain-scale properties and microstructure on the overall strength of the composite material Keywordscohesive-frictional materials\–linear comparison composite

}, isbn = {978-3-642-19629-4}, issn = {1866-8755}, doi = {10.1007/978-3-642-19630-0_15}, author = {J. Alberto Ortega and Gathier, Benjamin and Franz-Josef Ulm}, editor = {Wu, Wei and Borja, Ronaldo I.} } @article {288, title = {Tight binding within the fourth moment approximation: Efficient implementation and application to liquid Ni droplet diffusion on graphene}, journal = {Physical Review B}, volume = {84}, year = {2011}, month = {Aug-31-2011}, pages = { Article Number: 085455}, abstract = {

Application of the fourth moment approximation (FMA) to the local density of states within a tight binding description to build a reactive, interatomic interaction potential for use in large scale molecular simulations, is a logical and significant step forward to improve the second moment approximation, standing at the basis of several, widely used (semi-)empirical interatomic interaction models. In this paper we present a sufficiently detailed description of the FMA and its technical implications, containing the essential elements for an efficient implementation in a simulation code. Using a recent, existing FMA-based model for C-Ni systems, we investigated the size dependence of the diffusion of a liquid Ni cluster on a graphene sheet and find a power law dependence of the diffusion constant on the cluster size (number of cluster atoms) with an exponent very close to \−2/3, equal to a previously found exponent for the relatively fast diffusion of solid clusters on a substrate with incommensurate lattice matching. The cluster diffusion exponent gives rise to a specific contribution to the cluster growth law, which is due to cluster coalescence. This is confirmed by a simulation for Ni cluster growth on graphene, which shows that cluster coalescence dominates the initial stage of growth, overruling Oswald ripening.

}, issn = {1098-0121}, doi = {10.1103/PhysRevB.84.085455}, author = {Los, J. H. and Christophe Bichara and Roland Jean-Marc Pellenq} }