@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 {663, title = {Grains3D, a flexible DEM approach for particles of arbitrary convex shape{\textemdash}Part III: extension to non-convex particles modelled as glued convex particles}, journal = {Computational Particle Mechanics}, volume = {106}, year = {2019}, month = {Jan-2019}, pages = {55 - 84}, abstract = {

Large-scale numerical simulation using the discrete element method (DEM) contributes to improving our understanding of granular flow dynamics involved in many industrial processes and geophysical flows. In industry, it leads to an enhanced design and an overall optimization of the corresponding equipment and process. Most of the DEM simulations in the literature have been performed using spherical particles. A limited number of studies dealt with non-spherical particles, even less with non-convex particles. Even convex bodies do not always represent the real shape of certain particles. In fact, more complex-shaped particles are found in many industrial applications, for example, catalytic pellets in chemical reactors or crushed glass debris in recycling processes. In Grains3D-Part I (Wachs et al. in Powder Technol 224:374-389, 2012), we addressed the problem of convex shape in granular simulations, while in Grains3D-Part II (Rakotonirina and Wachs in Powder Technol 324:18-35, 2018), we suggested a simple though efficient parallel strategy to compute systems with up to a few hundreds of millions of particles. The aim of the present study is to extend even further the modelling capabilities of Grains3D towards non-convex shapes, as a tool to examine the flow dynamics of granular media made of non-convex particles. Our strategy is based on decomposing a non-convex-shaped particle into a set of convex bodies, called elementary components. We call our method glued or clumped convex method, as an extension of the popular glued sphere method. Essentially, a non-convex particle is constructed as a cluster of convex particles, called elementary components. At the level of these elementary components of a glued convex particle, we employ the same contact detection strategy based on a Gilbert-Johnson-Keerthi algorithm and a linked-cell spatial sorting that accelerates the resolution of the contact, that we introduced in [39]. Our glued convex model is implemented as a new module of our code Grains3D and is therefore automatically fully parallel. We illustrate the new modelling capabilities of Grains3D in two test cases: (1) the filling of a container and (2) the flow dynamics in a rotating drum.

}, keywords = {Granular flow; Discrete element method; Non-convex shape; GJK algorithm; Glued convex}, issn = {2196-4378}, doi = {10.1007/s40571-018-0198-3}, url = {http://link.springer.com/10.1007/s40571-018-0198-3}, author = {Rakotonirina, Andriarimina Daniel and Jean-Yves Delenne and Farhang Radja{\"\i} and Wachs, Anthony} } @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 {667, title = {Parallel implicit contact algorithm for soft particle systems}, journal = {Computer Physics Communications}, volume = {237}, year = {2019}, month = {Apr-01-2019}, pages = {17 - 25}, abstract = {

This paper presents a numerical technique to model soft particle materials in which the particles can undergo large deformations. It combines an implicit finite strain formalism of the Material Point Method and the Contact Dynamics method. In this framework, the large deformations of individual particles as well as their collective interactions are treated consistently. In order to reduce the computational cost, this method is parallelised using the Message Passing Interface (MPI) strategy. Using this approach, we investigate the uniaxial compaction of 2D packings composed of particles governed by a Neo-Hookean material behaviour. We consider compressibility rates ranging from fully compressible to incompressible particles. The packing deformation mechanism is a combination of both particle rearrangements and large deformations, and leads to high packing fractions beyond the jamming state. We show that the packing strength declines when the particle compressibility decreases, and the packing can deform considerably. We also discuss the evolution of the connectivity of the particles and particle deformation distributions in the packing. (C) 2018 Elsevier B.V. All rights reserved.

}, issn = {00104655}, doi = {10.1016/j.cpc.2018.10.030}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0010465518303904}, author = {Saeid Nezamabadi and Frank, Xavier and Jean-Yves Delenne and Julien Averseng and Farhang Radja{\"\i}} } @book {635, title = {ACS Symposium SeriesGels and Other Soft Amorphous Solids Heterogeneity in Cement Hydrates}, volume = {1296}, year = {2018}, pages = {357-371}, publisher = {American Chemical Society}, organization = {American Chemical Society}, address = {Washington, DC}, abstract = {

Cement hydrates named C-S-H are the main products of the reaction of cement with water. The C-S-H phase is the most important phase of cement paste as it glues all other phases together in a solid rock-like material. C-S-H gels form and densify via out-of-equilibrium precipitation and aggregation of nano-grains during cement hydration. In this chapter, the link between the making and densification of C-S-H gels and amorphous solids is discussed by coarse-grained models based on the evolution of interaction potentials and an out-of-equilibrium simulation approach for particle precipitation. In particular, we characterize and correlate mesoscale structural and mechanical heterogeneities resulting into residual local eigenstresses. This underlying microscopic picture explains recent macroscopic measurements of the volume change of hydrating cement in fully saturated conditions.

}, isbn = {0-8412-3316-0}, issn = {0097-6156}, doi = {10.1021/symposium10.1021/bk-2018-129610.1021/bk-2018-1296.ch018}, url = {http://pubs.acs.org/series/symposiumhttp://pubs.acs.org/doi/book/10.1021/bk-2018-1296}, author = {Katerina Ioannidou}, editor = {Horkay, Ferenc and Douglas, Jack F. and Emanuela Del Gado} } @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 {578, title = {Doping as a Way To Protect Silicate Chains in Calcium Silicate Hydrates}, journal = {ACS Sustainable Chemistry \& Engineering}, volume = {6}, year = {2018}, month = {Sep-09-2018}, pages = {15015 - 15021}, abstract = {

A critical challenge in reducing anthropogenic impacts on the environment is to decrease the carbon footprint of the cement industry. A key concern in the search for more sustainable cement designs is the understanding and control of the depolymerization process that eventually determines the integrity of their silicate chains under mechanical, chemical, or thermal stresses. Herein, we use metadynamics to show that the depolymerization of cement silicate skeletons consists of hydroxylation followed by bond-breaking. We then clarify the local effects of doping the silicate chains: a stable pentacoordinate state following hydroxylation is promoted by aluminum atoms but restrained by phosphorus additions, the presence of two dopants being related to energy landscapes less favorable to bond-breaking. The role of these dopants is explained in cement-based materials and is key to the quest for low-cost opportunities to preserve the strength of cement for high temperatures or even over time.

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}, keywords = {Bond-breaking; Calcium silicate hydrate; Doping; Green cement; Silicate chains}, issn = {2168-0485}, doi = {10.1021/acssuschemeng.8b03488}, url = {http://pubs.acs.org/doi/10.1021/acssuschemeng.8b03488}, author = {Dupuis, Romain and Dolado, Jorge S. and Surga, Jose and Ayuela Andr{\'e}s} } @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 {580, title = {Improving the practicality and safety of artificial corneas: Pre-assembly and gamma-rays sterilization of the Boston Keratoprosthesis}, journal = {The Ocular Surface}, volume = {16}, year = {2018}, month = {Jul-2018}, pages = {322 - 330}, abstract = {

Purpose: To make the Boston keratoprosthesis (B-KPro), together with its carrier corneal graft, more easily procured, transported and stored, as well as less expensive, easier for the surgeon to implant and safer for the patient, it is proposed that the B-KPro-graft combination be pre-assembled by an expert technician, followed by sterilization with gamma ray irradiation (GI) allowing long-term storage at room temperature. For this to be possible, it must be shown that the B-KPro itself (not only the graft) remains unharmed by the irradiation.

Methods: Polymethyl methacrylate (PMMA) discs and B-KPros were submitted to either ethylene oxide sterilization or different doses of GI. Cell biocompatibility, mechanical strength and optical quality were evaluated. The feasibility of assembling the B-KPro to a corneal graft, and gamma-radiate afterwards, was also assessed.

Results: There were no differences in cell biocompatibility between the samples. The optical evaluation showed high levels of transparency for all the groups. The absorbance of ultraviolet was higher for the groups treated with GI. The mechanical evaluation by nanoindentation showed no alterations of the PMMA discs after GI. The flexure test revealed a similar mechanical behavior. Technically, pre-assembly and GI of the B-KPro revealed no problems.

Conclusions: Sterilization of B-KPro using GI has no detrimental influence on the device. The pre-assembly of B-KPro to a donor cornea, followed by gamma sterilization, emerges as an efficient and safe procedure. (C) 2018 Elsevier Inc. All rights reserved.

}, keywords = {Artificial corneas; Boston keratoprosthesis; Gamma radiation; Gamma rays; Preassembly; Sterilization; Polymethyl methacrylate}, issn = {15420124}, doi = {10.1016/j.jtos.2018.04.002}, url = {https://linkinghub.elsevier.com/retrieve/pii/S1542012418300442}, author = {Gonzalez-Andrades, Miguel and Sharifi, Roholah and Islam, Mohammad Mirazul and Divoux, Thibaut and Haist, Michael and Paschalis, Eleftherios I. and Gelfand, Larisa and Mamodaly, Shamina and Di Cecilia, Luca and Cruzat, Andrea and Franz-Josef Ulm and Chodosh, James and Delori, Francois and Dohlman, Claes H.} } @article {533, title = {Mechanical strength of wet particle agglomerates}, journal = {Mechanics Research Communications}, volume = {92}, year = {2018}, month = {Sep-2018}, pages = {1 - 7}, abstract = {

Using particle dynamics simulations, we investigate the strength and microstructure of agglomerates of wet frictional particles subjected to axial compression. The numerical model accounts for the cohesive and viscous effects of the binding liquid up to a debonding distance with the liquid assumed to be distributed homogeneously inside the agglomerate. We show that wet agglomerates undergo plastic deformation due to the rearrangements of primary particles during compression. The compressive strength is thus characterized by the plastic threshold before the onset of failure by the irreversible loss of wet contacts between primary particles. We find that the agglomerate plastic threshold is proportional to the characteristic cohesive stress defined from the liquid-vapor surface tension and the mean diameter of primary particles, with a prefactor that is a nearly linear function of the debonding distance and increases with size span. We analyze the agglomerate microstructure and, considering only the cohesive capillary forces at all bonds between primary particles, we propose an expression of the plastic strength as a function of the texture parameters such as the wet coordination number and packing fraction. This expression is shown to be consistent with our simulations up to a multiplicative factor reflecting the distribution of the capillary bridges. (C) 2018 Published by Elsevier Ltd.

Fig. 1. Schematic drawing of the forces acting on particle i by a contacting particle j{\textellipsis}

Fig. 2. Schematic representation of diametrical compression test (a), and snapshots of{\textellipsis}

Fig. 3. Snapshot of a granule under diametrical compression for α=1

Fig. 4. Vertical strength σzz normalized by the reference stress σc for different{\textellipsis}

Fig. 5. Normalized plastic strength of the granule for several values of the debonding{\textellipsis}

Fig. 6. Normalized plastic strength σp/σc of the granules for different values of the{\textellipsis}

Fig. 7. The initial wet coordination number Z0 of the granules for different values of{\textellipsis}

Fig. 8. The prefactor η in Eq

Fig. 9. The ZΦs in Eq

}, issn = {00936413}, doi = {10.1016/j.mechrescom.2018.07.003}, url = {https://www-sciencedirect-com.libproxy.mit.edu/science/article/pii/S0093641318301216}, author = {Vo, Thanh-Trung and Patrick Mutabaruka and Saeid Nezamabadi and Jean-Yves Delenne and Izard, Edouard and Roland Jean-Marc Pellenq and Farhang Radja{\"\i}} } @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 {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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Figure

Figure

Figure

Figure

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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 {629, title = {Time-Resolved Mechanical Spectroscopy of Soft Materials via Optimally Windowed Chirps}, journal = {Physical Review X}, volume = {8}, year = {2018}, month = {Dec-06-2018}, pages = {Article Number 041042 }, abstract = {

The ability to measure the bulk dynamic behavior of soft materials with combined time and frequency resolution is instrumental for improving our fundamental understanding of connections between the microstructural dynamics and the macroscopic mechanical response. Current state-of-the-art techniques are often limited by a compromise between resolution in the time and frequency domains, mainly due to the use of elementary input signals that have not been designed for fast time-evolving systems such as materials undergoing gelation, curing, or self-healing. In this work, we develop an optimized and robust excitation signal for time-resolved mechanical spectroscopy through the introduction of joint frequency- and amplitude-modulated exponential chirps. Inspired by the biosonar signals of bats and dolphins, we optimize the signal profile to maximize the signal-to-noise ratio while minimizing spectral leakage with a carefully designed modulation of the envelope of the chirp, obtained using a cosine-tapered window function. A combined experimental and numerical investigation reveals that there exists an optimal range of window profiles (around 10\% of the total signal length) that minimizes the error with respect to standard single-frequency sweep techniques. The minimum error is set by the noise floor of the instrument, suggesting that the accuracy of an optimally windowed-chirp (OWCh) sequence is directly comparable to that achievable with a standard frequency sweep, while the acquisition time can be reduced by up to 2 orders of magnitude, for comparable spectral content. Finally, we demonstrate the ability of this optimized signal to provide time- and frequency-resolved rheometric data by studying the fast gelation process of an acid-induced protein gel using repeated OWCh pulse sequences. The use of optimally windowed chirps enables a robust time-resolved rheological characterization of a wide range of soft materials undergoing rapid mutation and has the potential to become an invaluable rheometric tool for researchers across different disciplines.

}, doi = {10.1103/PhysRevX.8.041042}, url = {https://link.aps.org/doi/10.1103/PhysRevX.8.041042}, author = {Geri, Michela and Keshavarz, Bavand and Divoux, Thibaut and Clasen, Christian and Curtis, Daniel J. and McKinley, Gareth H.} } @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 {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 {602, title = {Compaction of granular materials composed of deformable particles}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 05013}, abstract = {

In soft particle materials such as metallic powders the particles can undergo large deformations without rupture. The large elastic or plastic deformations of the particles are expected to strongly affect the mechanical properties of these materials compared to hard particle materials more often considered in research on granular materials. Herein, two numerical approaches are proposed for the simulation of soft granular systems: (i) an implicit formulation of the Material Point Method (MPM) combined with the Contact Dynamics (CD) method to deal with contact interactions, and (i) Bonded Particle Model (BPM), in which each deformable particle is modeled as an aggregate of rigid primary particles using the CD method. These two approaches allow us to simulate the compaction of an assembly of elastic or plastic particles. By analyzing the uniaxial compaction of 2D soft particle packings, we investigate the effects of particle shape change on the stress-strain relationship and volume change behavior as well as the evolution of the microstructure.

}, doi = {10.1051/epjconf/201714005013}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714005013}, author = {Thanh Hai Nguyen and Saeid Nezamabadi and Jean-Yves Delenne and Farhang Radja{\"\i}}, editor = {Luding, S.} } @article {614, title = {Conformal field theory of critical Casimir forces between surfaces with alternating boundary conditions in two dimensions}, journal = {Journal of Statistical Mechanics: Theory and Experiment}, year = {2017}, month = {Mar-2017}, pages = { Article Number 033201 }, abstract = {

Systems as diverse as binary mixtures and inclusions in biological membranes, and many more, can be described effectively by interacting spins. When the critical fluctuations in these systems are constrained by boundary conditions, critical Casimir forces (CCF) emerge. Here we analyze CCF between boundaries with alternating boundary conditions in two dimensions, employing conformal field theory (CFT). After presenting the concept of boundary changing operators, we specifically consider two different boundary configurations for a strip of critical Ising spins: (I) alternating equi-sized domains of up and down spins on both sides of the strip, with a possible lateral shift, and (II) alternating domains of up and down spins of different size on one side and homogeneously fixed spins on the other side of the strip. Asymptotic results for the CCF at small and large distances are derived. We introduce a novel modified Szego formula for determinants of real antisymmetric block Toeplitz matrices to obtain the exact CCF and the corresponding scaling functions at all distances. We demonstrate the existence of a surface renormalization group flow between universal force amplitudes of different magnitude and sign. The Casimir force can vanish at a stable equilibrium position that can be controlled by parameters of the boundary conditions. Lateral Casimir forces assume a universal simple cosine form at large separations.

}, keywords = {Casimir effect; conformal field theory; critical exponents and amplitudes}, doi = {10.1088/1742-5468/aa5a68}, url = {http://stacks.iop.org/1742-5468/2017/i=3/a=033201?key=crossref.e58e04fb8593248b573c53589bed0f1d}, author = {Dubail, Jerome and Santachiara, Raoul and Emig, Thorsten} } @article {601, title = {Effect of particle size distribution on 3D packings of spherical particles}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 02030}, abstract = {

We use molecular dynamics simulations of frictionless spherical particles to investigate a class of polydisperse granular materials in which the particle size distribution is uniform in particle volumes. The particles are assembled in a box by uniaxial compaction under the action of a constant stress. Due to the absence of friction and the nature of size distribution, the generated packings have the highest packing fraction at a given size span, defined as the ratio of the largest size to the smallest size. We find that, up to = 5, the packing fraction is a nearly linear function of . While the coordination number is nearly constant due to the isostatic nature of the packings, we show that the connectivity of the particles evolves with . In particular, the proportion of particles with 4 contacts represents the largest proportion of particles mostly of small size. We argue that this particular class of particles occurs as a result of the high stability of local configurations in which a small particle is stuck by four larger particles.

}, doi = {10.1051/epjconf/201714002030}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714002030}, author = {Taiebat, Mahdi and Patrick Mutabaruka and Roland Jean-Marc Pellenq and Farhang Radja{\"\i}}, editor = {Saeid Nezamabadi and Luding, S. and Jean-Yves Delenne} } @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 {584, title = {Impact of saccharides on the drying kinetics of agarose gels measured by in-situ interferometry}, journal = {Scientific Reports}, volume = {7}, year = {2017}, month = {Jan-23-2017}, pages = { Article Number: 41185 }, abstract = {

Agarose gels are viscoelastic soft solids that display a porous microstructure filled with water at 90\% w/w or more. Despite an extensive use in food industry and microbiology, little is known about the drying kinetics of such squishy solids, which suffers from a lack of time-resolved local measurements. Moreover, only scattered empirical observations are available on the role of the gel composition on the drying kinetics. Here we study by in-situ interferometry the drying of agarose gels of various compositions cast in Petri dishes. The gel thinning is associated with the displacement of interference fringes that are analyzed using an efficient spatiotemporal filtering method, which allows us to assess local thinning rates as low as 10 nm/s with high accuracy. The gel thinning rate measured at the center of the dish appears as a robust observable to quantify the role of additives on the gel drying kinetics and compare the drying speed of agarose gels loaded with various non-gelling saccharides of increasing molecular weights. Our work shows that saccharides systematically decrease the agarose gel thinning rate up to a factor two, and exemplifies interferometry as a powerful tool to quantify the impact of additives on the drying kinetics of polymer gels.

}, doi = {10.1038/srep41185}, url = {http://www.nature.com/articles/srep41185}, author = {Mao, Bosi and Divoux, Thibaut and Snabre, Patrick} } @article {245, title = {Inhomogeneity in Cement Hydrates: Linking Local Packing to Local Pressure}, journal = {Journal of Nanomechanics and Micromechanics}, volume = {7}, year = {2017}, month = {Mar-03-2017}, pages = {Article Number: UNSP 04017003}, abstract = {

Nanoscale structural heterogeneities were recently revealed in computational and experimental studies of calcium silicate hydrates in hardened cement pastes. In this work their consequences for the mechanics are analyzed by computing local pressures in model samples at different overall densities, corresponding to different initial water-to-cement ratios. The correlations between pore size distributions, local density, local cohesive energy, and local pressure clearly show how in these materials structural heterogeneities may be the origin of significant mechanical heterogeneities. The results indicate that even at high density pressure, heterogeneities develop during the densification of cement hydrates and result in the coexistence of regions of high positive pressure with regions of negative pressure, in spite of the overall mechanical stability of the samples. Furthermore, the regions of negative pressure, prone to mechanical instabilities and local plastic processes, tend to be localized close to the surface of large mesopores and hence to be more significant at higher initial water content.
Inhomogeneity in Cement Hydrates: Linking Local Packing to Local Pressure. Available from: https://www.researchgate.net/publication/314222493_Inhomogeneity_in_Cement_Hydrates_Linking_Local_Packing_to_Local_Pressure [accessed Oct 2, 2017].

}, issn = {2153-5434}, doi = {10.1061/(ASCE)NM.2153-5477.0000120}, author = {Katerina Ioannidou and Emanuela Del Gado and Franz-Josef Ulm and Roland Jean-Marc Pellenq} } @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 {264, title = {Modeling Granular Materials: Century-Long Research across Scales}, journal = {Journal of Engineering Mechanics}, volume = {143}, year = {2017}, month = {Jan-23-2017}, pages = {Article Number: UNSP 04017002}, abstract = {

Granular materials are the most recurrent form of solid-state matter on Earth. They challenge researchers and engineers in various fields not only because they occur with a broad variety of grain sizes, shapes and interactions in nature and industry, but also because they show a rich panoply of mechanical states. Despite this polymorphism, all these different types of soils, powders, granules, ores, pharmaceutical products, etc., are instances of the granular matter with the same least common denominator of being sandlike (psammoid in Greek), i.e.,\ solid grains interacting via frictional contacts. This review describes milestone contributions to the field of granular materials since the early elastic-plastic models developed for soils in the 1950s. The research on granular materials has grown into a vast multidisciplinary field in the 1980s with increasing focus on the microstructure and owing to new experimental tools and discrete simulation methods. It turns out that the granular texture, particle-scale kinematics, and force transmission are far more complex than presumed in early micromechanical models of granular materials. Hence, constitutive relations cannot easily be derived from the particle-scale behavior although advanced continuum models have been developed to account for anisotropy, intermediate stress, and complex loading paths. The subtle elastic properties and origins of bulk friction will be discussed, as well as the effects of particle shape and size distributions. The review covers also recent developments in macroscopic modeling such as the thermomechanical approach, anisotropic critical state theory, nonlocal modeling approach, inertial flows, and material instabilities. Finally, a brief account is given of open issues and some new frontiers and challenges in the field.

}, issn = {0733-9399}, doi = {10.1061/(ASCE)EM.1943-7889.0001196}, author = {Farhang Radja{\"\i} and Jean-Noel~ Roux and Daouadji, Ali} } @article {606, title = {Modeling root growth in granular soils: effects of root stiffness and packing fraction}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 14013}, abstract = {

We use molecular dynamics simulations to investigate the effects of root bending stiffness and packing fraction on the path followed by a growing root in 2D packings of grains representing a soil. The root is modeled as a chain of elements that can grow in length and change their direction depending on the forces exerted by soil grains. We show that the root shape is mainly controlled by the bending stiffness of its apex. At low stiffness, the root randomly explores the pore space whereas at sufficiently high stiffness, of the order of soil hardness multiplied by mean grain size, the root follows a straight path across the soil. Between these two limits, the root shape can be characterized by the standard deviation of its re-directions at the scale of soil grains. We find that this shape parameter varies as a power-law function of the normalized bending stiffness.

}, doi = {10.1051/epjconf/201714014013}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714014013}, author = {Fakih, Mahmoud and Jean-Yves Delenne and Farhang Radja{\"\i} and Fourcaud, Thierry}, editor = {Saeid Nezamabadi and Luding, S.} } @article {265, title = {Modeling soft granular materials}, journal = {Granular Matter}, volume = {19}, year = {2017}, month = {Jun-17-2017}, pages = {Article Number: 8}, abstract = {

Soft-grain materials such as clays and other colloidal pastes share the common feature of being composed of grains that can undergo large deformations without rupture. For the simulation of such materials, we present two alternative methods: (1) an implicit formulation of the material point method (MPM), in which each grain is discretized as a collection of material points, and (2) the bonded particle model (BPM), in which each soft grain is modeled as an aggregate of rigid particles using the contact dynamics method. In the MPM, a linear elastic behavior is used for the grains. In order to allow the aggregates in the BPM to deform without breaking, we use long-range center-to-center attraction forces between the primary particles belonging to each grain together with steric repulsion at their contact points. We show that these interactions lead to a plastic behavior of the grains. Using both methods, we analyze the uniaxial compaction of 2D soft granular packings. This process is nonlinear and involves both grain rearrangements and large deformations. High packing fractions beyond the jamming state are reached as a result of grain shape change for both methods. We discuss the stress-strain and volume change behavior as well as the evolution of the connectivity of the grains. Similar textures are observed at large deformations although the BPM requires higher stress than the MPM to reach the same level of packing fraction.

}, issn = {1434-5021}, doi = {10.1007/s10035-016-0689-y}, author = {Saeid Nezamabadi and Thanh Hai Nguyen and Jean-Yves Delenne and Farhang Radja{\"\i}} } @proceedings {336, title = {Modelling Transient Dynamics of Granular Slopes: MPM and DEM}, journal = {PROCEEDINGS OF THE 1ST INTERNATIONAL CONFERENCE ON THE MATERIAL POINT METHOD (MPM 2017) Book Series: Procedia Engineering }, volume = {175}, year = {2017}, month = {Jul-17-2017}, pages = {94 - 101}, publisher = {Elsevier Ltd.}, address = {JAN 10-13, 2017, Delft, NETHERLANDS}, abstract = {

Transient granular flows, such as rock falls, debris flows, and aerial and submarine avalanches, occur very often in nature. In the geotechnical context, transient movements of large granular slopes are a substantial factor of risk due to their destructive force and the transformations the y may produce in the landscape. This paper investigates the ability of MPM, a continuum approach, to reproduce the evolution of a granular slope destabilised by an external energy source. In particular, a central issue is whether the power-law dependence of run-out distance and time observed with respect to the initial geometry or energy can be reproduced by a simple Mohr-Coulomb plastic behaviour. The effect of base friction on the run-out kinematics is studied by comparing the data obtained from the DEM and MPM simulations. The mechanism of energy dissipation is primarily through friction and the MPM is able to predict the run-out response in good agreement with the DEM simulations. At very low excitation energies, the DEM simulations show longer run-out in comparison to the MPM due to local destabilization at the flow front. At low input energies, a larger fraction of the energy is consumed in the destabilisation process, hence the amount energy available for flow is less. However, at higher input energy, where most of the energy is dissipated during the spreading phase, the run-out distance has a weak dependence on the distribution of velocity in the granular mass.

}, issn = {18777058}, doi = {10.1016/j.proeng.2017.01.032}, author = {Krishna Kumar and Kenichi Soga and Jean-Yves Delenne and Farhang Radja{\"\i}}, editor = {Rohe, A and Kenichi Soga and Teunissen, H} } @proceedings {337, title = {MPM with Frictional Contact for Application to Soft Particulate Materials}, journal = {PROCEEDINGS OF THE 1ST INTERNATIONAL CONFERENCE ON THE MATERIAL POINT METHOD (MPM 2017) Book Series: Procedia Engineering }, volume = {175}, year = {2017}, month = {Mar-23-2017}, pages = {141 - 147}, publisher = {Elsevier Ltd.}, address = {JAN 10-13, 2017, Delft, NETHERLANDS}, abstract = {

Soft particle materials are composed of discrete particles that can undergo large deformations without rupture. Most food products, many powders, colloidal pastes, vesicles and biological cells are soft particle systems. In order to model such materials, we present an efficient numerical approach combining an implicit formulation of the Material Point Method (MPM) and Contact Dynamics (CD) method. The MPM deals with bulk variables of an individual particle by discretizing it as a collection of material points, whereas the CD allows for the treatment of frictional contacts between particles. This model is applied for the simulation of the uniaxial compression of 2D soft-particle packings. The compaction is a nonlinear process in which new contacts are formed between particles and the contact areas increase. The change of particle shapes allows these materials to reach high packing fraction. We find that the contact specific surface, the orientation anisotropy and the aspect ratio of particles increase as a function of the packing fraction but at different rates. We also evidence the effect of friction, which favors strong stress chains and thus the elongation of particles, leading to larger values of the orientation anisotropy and the aspect ratio at a given level of packing fraction as compared to a frictionless particle packing.

}, issn = {18777058}, doi = {10.1016/j.proeng.2017.01.044}, author = {Saeid Nezamabadi and Thanh Hai Nguyen and Jean-Yves Delenne and Julien Averseng and Frank, Xavier and Farhang Radja{\"\i}}, editor = {Rohe, A and Kenichi Soga and Teunissen, H} } @article {623, title = {Nano-granular texture of cement hydrates}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 15027}, abstract = {

Mechanical behavior of concrete crucially depends on cement hydrates, the \“glue\” of cement. The design of high performance and more environmentally friendly cements demands a deeper understanding of the formation of the multiscale structure of cement hydrates, when they precipitate and densify. We investigate the precipitation and setting of nano-grains of cement hydrates using a combination of Monte Carlo and Molecular Dynamics numerical simulations and study their texture from nano up to the micron scale. We characterize the texture of cement hydrates using the local volume fraction distribution, the pore size distribution, the scattering intensity and the chord length distribution and we compare them with experiments. Our nano-granular model provides cement structure with realistic texture and mechanics and can be further used to investigate degradation mechanisms.

}, doi = {10.1051/epjconf/201714015027}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714015027}, author = {Katerina Ioannidou and Franz-Josef Ulm and Pierre E. Levitz and Emanuela Del Gado and Roland Jean-Marc Pellenq}, editor = {Farhang Radja{\"\i} and Saeid Nezamabadi and Luding, S. and Jean-Yves Delenne} } @article {582, title = {Nonlinear Viscoelasticity and Generalized Failure Criterion for Polymer Gels}, journal = {ACS Macro Letters}, volume = {6}, year = {2017}, month = {Jun-12--2017}, pages = {663 - 667}, abstract = {

Polymer gels behave as soft viscoelastic solids and exhibit a generic nonlinear mechanical response characterized by pronounced stiffening prior to irreversible failure, most often through macroscopic fractures. Here, we describe this scenario for a model protein gel using an integral constitutive equation built upon the linear and the nonlinear viscoelastic properties of the gel. We show that this formalism predicts quantitatively the gel mechanical response in shear start-up experiments, up to the onset of macroscopic failure. Moreover, we couple the computed stress response with Bailey\&$\#$39;s durability criterion for brittle solids in order to predict the critical values of the stress sigma(c) and strain gamma(c) at failure. The excellent agreement between theory and experiments suggests that failure in this soft viscoelastic gel is a Markovian process and that Bailey\&$\#$39;s failure criterion extends beyond hard materials such as metals, glasses, or minerals.

}, issn = {2161-1653}, doi = {10.1021/acsmacrolett.7b00213}, url = {http://pubs.acs.org/doi/10.1021/acsmacrolett.7b00213}, author = {Keshavarz, Bavand and Divoux, Thibaut and Manneville, S{\'e}bastien and McKinley, Gareth H.} } @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 {608, title = {Numerical modeling of the tensile strength of a biological granular aggregate: Effect of the particle size distribution}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 08013}, 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.

}, doi = {10.1051/epjconf/201714008013}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714008013}, author = {Heinze, Karsta and Frank, Xavier and Val{\'e}rie Lullien-Pellerina and George, Matthieu and Farhang Radja{\"\i} and Jean-Yves Delenne}, editor = {Saeid Nezamabadi and Luding, S.} } @article {603, title = {Numerical study of the failure of materials embedding soft to hard particles}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 02029}, abstract = {

In this study, we use a bond-based peridynamic approach to investigate the mechanical strength and cracking of composite materials with spherical inclusions. The total volume fraction of particles and the particle-matrix toughness ratio were varied to cover a range of soft to hard inclusions. The mean particle damage was characterized together with crack patterns at a sub-particle scale. Three types of crack patterns are identified depending on the toughness ratio.

}, doi = {10.1051/epjconf/201714002029}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714002029}, author = {Frank, Xavier and Jean-Yves Delenne and Farhang Radja{\"\i}}, 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 {622, title = {The Potential of Mean Force concept for bridging (length and time) scales in the modeling of complex porous materials}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 01009}, abstract = {

We introduce the concept of Potential of Mean Force, PMF, as a way to implement upscaling modeling from the nano-scale to micron-scale. A PMF is a free energy function representing in an effective way the interactions between objects (cement hydrates, clay platelets, etc.) at thermodynamics conditions. The PMF is therefore the key piece of information allowing to coarse-grained Physical-Chemistry information in a meso-scale model formulation. The use of PMF offers a huge computational advantage as it allows a straight up-scaling to the meso-scale while keeping essential interactions information that are the hallmark of Physical-Chemistry processes. Such a coarse-grained modeling integrates atomistic response into inter-particle potentials that fully propagate molecular scale information all the way to the meso-scale.

}, doi = {10.1051/epjconf/201714001009}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714001009}, author = {Katerina Ioannidou and Benoit Carrier and Matthieu Vandamme and Roland Jean-Marc Pellenq}, editor = {Farhang Radja{\"\i} and 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 {607, title = {Scaling behavior of immersed granular flows}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 09044}, abstract = {

The shear behavior of granular materials immersed in a viscous fluid depends on fluid properties (viscosity, density), particle properties (size, density) and boundary conditions (shear rate, confining pressure). Using computational fluid dynamics simulations coupled with molecular dynamics for granular flow, and exploring a broad range of the values of parameters, we show that the parameter space can be reduced to a single parameter that controls the packing fraction and effective friction coefficient. This control parameter is a modified inertial number that incorporates viscous effects.

}, doi = {10.1051/epjconf/201714009044}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714009044}, author = {L. Amarsid and Jean-Yves Delenne and Patrick Mutabaruka and Yann Monerie and Perales, F. and Farhang Radja{\"\i}}, editor = {Saeid Nezamabadi and Luding, S.} } @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 {599, title = {Strength of wet agglomerates of spherical particles: effects of friction and size distribution}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 08021}, abstract = {

We investigate the mechanical behavior of wet granular agglomerates composed of spherical particles by means of molecular dynamics simulations. The capillary cohesion force is modeled as an attraction force at the contact between two particles and expressed as an explicit function of the gap and volume of the liquid bridge. We are interested in the effect of the friction coefficient between primary particles. The agglomerates are subjected to diametrical compression tests. We find that the deformation is ductile involving particle rearrangements. However, a well-defined stress peak is observed and the peak stress is used as a measure of the compressive strength of the agglomerate. The strength increases with friction coefficient but levels off at friction coefficients above 0.4. Furthermore, the compressive strength is an increasing function of particle size span.

}, doi = {10.1051/epjconf/201714008021}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714008021}, author = {Vo, Thanh-Trung and Patrick Mutabaruka and Jean-Yves Delenne and Saeid Nezamabadi and Farhang Radja{\"\i}}, editor = {Luding, S.} } @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 {583, title = {Understanding rheological hysteresis in soft glassy materials}, journal = {Soft Matter}, volume = {13}, year = {2017}, month = {Mar-07-2017}, pages = {1834-1852}, abstract = {

Motivated by recent experimental studies of rheological hysteresis in soft glassy materials, we study numerically strain rate sweeps in simple yield stress fluids and viscosity bifurcating yield stress fluids. Our simulations of downward followed by upward strain rate sweeps, performed within fluidity models and the soft glassy rheology model, successfully capture the experimentally observed monotonic decrease of the area of the rheological hysteresis loop with sweep time in simple yield stress fluids, and the bell shaped dependence of hysteresis loop area on sweep time in viscosity bifurcating fluids. We provide arguments explaining these two different functional forms in terms of differing tendencies of simple and viscosity bifurcating fluids to form shear bands during the sweeps, and show that the banding behaviour captured by our simulations indeed agrees with that reported experimentally. We also discuss the difference in hysteresis behaviour between inelastic and viscoelastic fluids. Our simulations qualitatively agree with the experimental data discussed here for four different soft glassy materials.

}, issn = {1744-683X}, doi = {10.1039/C6SM02581A}, url = {http://xlink.rsc.org/?DOI=C6SM02581A}, author = {Radhakrishnan, Rangarajan and Divoux, Thibaut and Manneville, S{\'e}bastien and Fielding, Suzanne M.} } @article {263, title = {Viscoinertial regime of immersed granular flows}, journal = {Physical Review E}, volume = {96}, year = {2017}, month = {Oct-10-2017}, pages = {Article Number: 012901}, abstract = {

By means of extensive coupled molecular dynamics\–lattice Boltzmann simulations, accounting for grain dynamics and subparticle resolution of the fluid phase, we analyze steady inertial granular flows sheared by a viscous fluid. We show that, for a broad range of system parameters (shear rate, confining stress, fluid viscosity, and relative fluid-grain density), the frictional strength and packing fraction can be described by a modified inertial number incorporating the fluid effect. In a dual viscous description, the effective viscosity diverges as the inverse square of the difference between the packing fraction and its jamming value, as observed in experiments. We also find that the fabric and force anisotropies extracted from the contact network are well described by the modified inertial number, thus providing clear evidence for the role of these key structural parameters in dense suspensions.

Figure

Figure

Figure

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Figure

}, issn = {2470-0045}, doi = {10.1103/PhysRevE.96.012901}, author = {L. Amarsid and Jean-Yves Delenne and Patrick Mutabaruka and Yann Monerie and Perales, F. and Farhang Radja{\"\i}} } @article {598, title = {Wall roughness and nonlinear velocity profiles in granular shear flows}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 03090}, abstract = {

Inhomogeneous velocity profiles in granular flows are well known from both experiments and simulations, and considered as a hallmark of nonlocal behavior. By means of extensive contact dynamics simulations, we show that the sigmoidal velocity profiles in 2D flows of rigid disks are controlled by the roughness of driving boundary walls. We find that the velocity profile becomes linear for a critical value of wall roughness up to an exponential decay close to the walls with a characteristic length that does not depend on the flow thickness and rate. We describe the velocity profiles by introducing a state parameter that carries wall perturbation. By assuming that the local shear rate is a linear function of the state parameter, we obtain an analytical expression that fits velocity profiles. In this model, the nonlinear velocity profiles are explained in terms of the effects of wall roughness as boundary condition for the state parameter.

}, doi = {10.1051/epjconf/201714003090}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714003090}, author = {Schuhmacher, Paul and Farhang Radja{\"\i} and St{\'e}phane Roux}, editor = {Saeid Nezamabadi and Luding, S. and Jean-Yves Delenne} } @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 {637, title = {Adsorption in heterogeneous porous media: Hierarchical and composite solids}, journal = {Microporous and Mesoporous Materials}, volume = {229}, year = {2016}, month = {Jul-15-2016}, pages = {145 - 154}, abstract = {

Experiment and molecular simulation are used to investigate adsorption in heterogeneous porous media consisting of hierarchical solids (combining different porosity scales) or composite solids (such as silver nanoparticles adsorbed at the external surface of zeolite). It is shown that adsorption in such heterogeneous materials can be written as a linear combination of the adsorption isotherms in its different domains (i.e. porosity scales for the hierarchical sample and constituents for the composite sample). In the case of the composite material, we also show that the linear combination can be used with weighing parameters obtained for a different adsorbate. Such a superimposition principle, which is validated using well-characterized experimental samples, is of interest for characterization purpose as well as industrial applications as they can be used to determine accurately the amount of phases in a given sample (volume corresponding to a given porosity scale or constituent). In contrast, significant departure between the experimental adsorption isotherm and the linear combination can be used to detect coupling effects between the different domains or restrained access to a given domain type. Such a characterization strategy of complex heterogeneous media is complementary to other experiments, such as those probing capillary hysteresis shapes, scanning curves and subloops, which allow determining the distribution of domains within the framework of the independent domain theory. (C) 2016 Elsevier Inc. All rights reserved.

}, issn = {13871811}, doi = {10.1016/j.micromeso.2016.04.011}, url = {https://linkinghub.elsevier.com/retrieve/pii/S1387181116301032}, author = {Deliere, Ludovic and Fran{\c c}ois Villemot and David Farrusseng and Anne Galarneau and Topin, Sylvain and Benoit A. Coasne} } @article {267, title = {Bottom-up model for understanding the effects of wheat endosperm microstructure on its mechanical strength}, journal = {Journal of Food Engineering}, volume = {190}, year = {2016}, month = {Dec-2016}, pages = {40 - 47}, abstract = {

Wheat flours are essential ingredients of daily food products like bread, cookies or pastries. Their quality depends on the milling process and mechanical strength of wheat grains. Although it is well known that the strength and rupture of grains are strongly controlled by the endosperm microstructure, the respective roles of the starch and polymer volume fractions and their adhesion are not yet fully understood. This typical biological microstructure can be modeled as a cemented granular material, where the two size populations of starch granules (large:A-type, small:B-type) are the particles, and the protein matrix, which partially fills the space between granules, plays the role of a cement. This structural model of wheat endosperm is used, together with mechanical characteristics of starch and proteins obtained by means of Atomic Force Microscopy (AFM) measurements, to simulate the mechanical behavior and breakage of wheat endosperm in milling process. We find that the porosity outweighs the effect of other parameters for the elastic modulus, which declines as a nearly linear function of porosity. We also show that the tensile strength is an increasing function of the amount and connectivity of starch granules with increasing concentration of stresses along chains of granules. This effect is more significant at low porosity where stress distribution is mainly controlled by the contact network between starch granules. This effect explains why the protein content is not fully correlated to vitreousness, and samples of similar protein content can be different in vitreosity. Finally, we find that the starch-granule adhesion strongly affects the tensile strength whereas the effect of starch volume fraction appears mainly at high interface adhesion, which is the case of hard type wheat grains.

Fig.1. (a) Scanning Electron Micrograph of the fracture surface of a soft wheat{\textellipsis}

Fig.2. Illustration of the lattice approach for one step: (1) Initial lattice state{\textellipsis}

Fig.3. (a) Bidisperse granular sample generated with DEM for the highest starch volume{\textellipsis}

Fig.4. Example of samples submitted to tensile tests: (a) Maps of vertical stress{\textellipsis}

Fig.5. Stress-strain plots showing the effect of different values of the starch{\textellipsis}

Fig.6. Effective Young{\textquoteright}s modulus as a function of (a) protein volume fraction ρp and{\textellipsis}

}, issn = {02608774}, doi = {10.1016/j.jfoodeng.2016.06.009}, author = {Chichti, Emna and Val{\'e}rie Lullien-Pellerina and George, Matthieu and Farhang Radja{\"\i} and Rafik Aff{\`e}s and Jean-Yves Delenne} } @article {638, title = {Breakthrough in Xenon Capture and Purification Using Adsorbent-Supported Silver Nanoparticles}, journal = {Chemistry - A European Journal}, volume = {22}, year = {2016}, month = {Jul-04-2016}, pages = {9660-9666}, abstract = {

Rare gas capture and purification is a major challenge for energy, environment, and health applications. Of utmost importance for the nuclear industry, novel separation processes for Xe are urgently needed for spent nuclear fuel reprocessing and nuclear activity monitoring. The recovered, non-radioactive Xe is also of high economic value for lighting, surgical anesthetic, etc. Here, using adsorption and breakthrough experiments and statistical mechanics molecular simulation, we show the outstanding performance of zeolite-supported silver nanoparticles to capture/separate Xe at low concentrations (0.087-100 ppm). We also establish the efficiency of temperature swing adsorption based on such adsorbents for Xe separation from Kr/Xe mixtures and air streams corresponding to off-gases generated by nuclear reprocessing. This study paves the way for the development of novel, cost-efficient technologies relying on the large selectivity/capacity of adsorbent-supported silver nanoparticles which surpass all materials ever tested.

}, doi = {10.1002/chem.201601351}, url = {http://doi.wiley.com/10.1002/chem.201601351}, author = {Deliere, Ludovic and Benoit A. Coasne and Topin, Sylvain and Gr{\'e}au, Claire and Moulin, Christophe and David Farrusseng} } @article {643, title = {Cement As a Waste Form for Nuclear Fission Products: The Case of 90Sr and Its Daughters}, journal = {Environmental Science \& Technology}, volume = {49}, year = {2016}, month = {Nov-17-2016}, pages = {13676-13683}, abstract = {

One of the main challenges faced by the nuclear industry is the long-term confinement of nuclear waste. Because it is inexpensive and easy to manufacture, cement is the material of choice to store large volumes of radioactive materials, in particular the low-level medium-lived fission products. It is therefore of utmost importance to assess the chemical and structural stability of cement containing radioactive species. Here, we use ab initio calculations based on density functional theory (DFT) to study the effects of Sr-90 insertion and decay in C-S-H (calcium-silicate-hydrate) in order to test the ability of cement to trap and hold this radioactive fission product and to investigate the consequences of its beta-decay on the cement paste structure. We show that Sr-90 is stable when it substitutes the Ca2+ ions in C-S-H, and so is its daughter nucleus Y-90 after beta-decay. Interestingly, Zr-90, daughter of Y-90 and final product in the decay sequence, is found to be unstable compared to the bulk phase of the element at zero K but stable when compared to the solvated ion in water. Therefore, cement appears as a suitable waste form for Sr-90 storage.

}, issn = {0013-936X}, doi = {10.1021/acs.est.5b02609}, url = {http://pubs.acs.org/doi/10.1021/acs.est.5b02609}, author = {Dezerald, Lucile and Kohanoff, Jorge J. and Alfredo A. Correa and Caro, Alfredo and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Andres Sa{\`u}l} } @proceedings {338, title = {Contribution of mechanical factors to the variability of root architecture: Quantifying the past history of interaction forces between growing roots and soil grains}, journal = {2016 IEEE INTERNATIONAL CONFERENCE ON FUNCTIONAL-STRUCTURAL PLANT GROWTH MODELING, SIMULATION, VISUALIZATION AND APPLICATIONS (FSPMA)}, year = {2016}, month = {Nov-11-2016}, pages = {52-60}, publisher = {I E E E}, address = {NOV 07-11, 2016, Qingdao, PEOPLES R CHINA }, abstract = {

The relation between a growing root and the soil movement has often been under-estimated. The present work aims to determine how grains in granular soils are reorganized by the action of growing roots, and in turn how the resulting forces acting on root tips modify their development. For this purpose, we have developed a 2D Discrete Element Model (DEM) able to compute a numerical growth of a single root inside a granular medium, taking into account the grain-grain and the root-grain contact forces during the growth. First in silico simulations were carried out in order to : 1-quantify the influence of the granular structure (grain diameter distribution and gaps) and root mechanical properties (root bending stiffness) on the evolution of reaction forces applied to a single root during its growth; 2-highlight \“group effects\”, e.g. how the reorganization of grains and their interaction forces due to a given growing root can affect the mechanical signal perceived by its near neighbours; 3-investigate how the presence of initial channels within the granular medium can effect the growth trajectory and minimize the resistance to penetration. All simulations were carried out assuming that root growth direction was only driven by external forces. Simlation results allowed the extraction of general physical laws that will be used further to provide mechanoperceptive indicators and analyze experimental data provided by phenotyping platforms. The final objective will be to quantify the response of plants to mechanical stresses in terms of root elongation rate, root straightness and ramification.

}, doi = {10.1109/FSPMA.2016.7818288}, author = {Fakih, Mahmoud and Jean-Yves Delenne and Farhang Radja{\"\i} and Fourcaud, Thierry} } @article {621, title = {The crucial effect of early-stage gelation on the mechanical properties of cement hydrates}, journal = {Nature Communications}, volume = {7}, year = {2016}, month = {Jul-15-2016}, pages = {Article number 12106}, abstract = {

Gelation and densification of calcium\–silicate\–hydrate take place during cement hydration. Both processes are crucial for the development of cement strength, and for the long-term evolution of concrete structures. However, the physicochemical environment evolves during cement formation, making it difficult to disentangle what factors are crucial for the mechanical properties. Here we use Monte Carlo and Molecular Dynamics simulations to study a coarse-grained model of cement formation, and investigate the equilibrium and arrested states. We can correlate the various structures with the time evolution of the interactions between the nano-hydrates during the preparation of cement. The novel emerging picture is that the changes of the physicochemical environment, which dictate the evolution of the effective interactions, specifically favour the early gel formation and its continuous densification. Our observations help us understand how cement attains its unique strength and may help in the rational design of the properties of cement and related materials.

}, doi = {10.1038/ncomms12106}, url = {http://www.nature.com/articles/ncomms12106}, author = {Katerina Ioannidou and Matej, Kandu{\v c} and Li, Lunna and Frenkel, Daan and Dobnikar, Jure and Emanuela Del Gado} } @article {642, title = {How Ion Condensation Occurs at a Charged Surface: A Molecular Dynamics Investigation of the Stern Layer for Water{\textendash}Silica Interfaces}, journal = {The Journal of Physical Chemistry C}, volume = {120}, year = {2016}, month = {Jan-21-2016}, pages = {963-973}, abstract = {

We investigate the Stern layer of charged silicawater interfaces by calculating the ionsurface interaction from molecular dynamics simulations. The McMillanMayer potentials of mean force between a charged oxygen site and a lithium or cesium cation have been calculated. Contact ion pairs (CIPs) are important for the adsorption and desorption of ions, especially for lithium. An activation energy appears, which can result in a large estimated relaxation time. In the case of lithium, time scales needed to bind or unbind ions to and from the surface are found to be very long (up to the order of seconds for some surfaces), which implies that molecular dynamics cannot always be fully equilibrated. This work provides a new image of the Stern layer: it is not a continuous layer but a set of Bjerrum pairs. As a matter of fact, quantitative (macroscopic) treatments of such systems with localized surface charges require a three-dimensional model, contrary to the more commonly used one- or two-dimensional theoretical treatments.

}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.5b08836}, url = {http://pubs.acs.org/doi/10.1021/acs.jpcc.5b08836}, author = {Hocine, Sarah and Hartkamp, Remco and Bertrand Siboulet and Duvail, Magali and Benoit A. Coasne and Turq, P. and Jean-Francois Dufreche} } @article {266, title = {Lattice Boltzmann modelling of liquid distribution in unsaturated granular media}, journal = {Computers and Geotechnics}, volume = {80}, year = {2016}, month = {Dec-2016}, pages = {353 - 359}, 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 vapour 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. The tensile stress carried by the grains increases as a function of the amount of condensed liquid up to a peak in the funicular state beyond which the stress falls off as a result of pressure drop inside the merging clusters.

}, issn = {0266352X}, doi = {10.1016/j.compgeo.2016.02.017}, author = {Vincent Richefeu and Farhang Radja{\"\i} and Jean-Yves Delenne} } @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 {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 {585, title = {Simultaneous Rheoelectric Measurements of Strongly Conductive Complex Fluids}, journal = {Physical Review Applied}, volume = {6}, year = {2016}, month = {Dec-09-2016}, pages = { Article Number: 064004 }, abstract = {

We introduce an modular fixture designed for stress-controlled rheometers to perform simultaneous rheological and electrical measurements on strongly conductive complex fluids under shear. By means of a nontoxic liquid metal at room temperature, the electrical connection to the rotating shaft is completed with minimal additional mechanical friction, allowing for simultaneous stress measurements at values as low as 1 Pa. Motivated by applications such as flow batteries, we use the capabilities of this design to perform an extensive set of rheoelectric experiments on gels formulated from attractive carbon-black particles, at concentrations ranging from 4 to 15 wt \%. First, experiments on gels at rest prepared with different shear histories show a robust power-law scaling between the elastic modulus G(0)\&$\#$39; and the conductivity sigma(0) of the gels-i.e., G(0)\&$\#$39; similar to sigma(alpha)(0), with alpha = 1.65 +/- 0.04, regardless of the gel concentration. Second, we report conductivity measurements performed simultaneously with creep experiments. Changes in conductivity in the early stage of the experiments, also known as the Andrade-creep regime, reveal for the first time that plastic events take place in the bulk, while the shear rate gamma decreases as a weak power law of time. The subsequent evolution of the conductivity and the shear rate allows us to propose a local yielding scenario that is in agreement with previous velocimetry measurements. Finally, to establish a set of benchmark data, we determine the constitutive rheological and electrical behavior of carbon-black gels. Corrections first introduced for mechanical measurements regarding shear inhomogeneity and wall slip are carefully extended to electrical measurements to accurately distinguish between bulk and surface contributions to the conductivity. As an illustrative example, we examine the constitutive rheoelectric properties of five different grades of carbon-black gels and we demonstrate the relevance of this rheoelectric apparatus as a versatile characterization tool for strongly conductive complex fluids and their applications.

}, doi = {10.1103/PhysRevApplied.6.064004}, url = {https://link.aps.org/doi/10.1103/PhysRevApplied.6.064004}, author = {Helal, Ahmed and Divoux, Thibaut and McKinley, Gareth H.} } @article {179, title = {Advances in design and modeling of porous materials}, journal = {The European Physical Journal Special Topics}, volume = {224}, year = {2015}, month = {Jul-2015}, pages = {1653 - 1653}, abstract = {

This special issue of the European Physical Journal Special Topics is dedicated to selected papers from the symposium \“High surface area porous and granular materials\” organized in the frame of the conference \“Mat\ériaux 2014\”, held on November 24\–28, 2014 in Montpellier, France.

Porous materials and granular materials gather a wide variety of heterogeneous, isotropic or anisotropic media made of inorganic, organic or hybrid solid skeletons, with open or closed porosity, and pore sizes ranging from the centimeter scale to the sub-nanometer scale. Their technological and industrial applications cover numerous areas from building and civil engineering to microelectronics, including also metallurgy, chemistry, health, waste water and gas effluent treatment. Many emerging processes related to environmental protection and sustainable development also rely on this class of materials. Their functional properties are related to specific transfer mechanisms (matter, heat, radiation, electrical charge), to pore surface chemistry (exchange, adsorption, heterogeneous catalysis) and to retention inside confined volumes (storage, separation, exchange, controlled release). The development of innovative synthesis, shaping, characterization and modeling approaches enables the design of advanced materials with enhanced functional performance. The papers collected in this special issue offer a good overview of the state-of-the-art and science of these complex media.

We would like to thank all the speakers and participants for their contribution to the success of the symposium. We also express our gratitude to the organization committee of \“Mat\´eriaux 2014\”. We finally thank the reviewers and the staff of the European Physical Journal Special Topics who made the publication of this special issue possible.

}, issn = {1951-6355}, doi = {10.1140/epjst/e2015-02487-6}, author = {Ayral, Andre and Calas-Etienne, Sylvie and Benoit A. Coasne and Deratani, Andr{\'e} and Evstratov, Alexis and Anne Galarneau and Grande, Daniel and Hureau, Matthieu and Jobic, Herv{\'e} and Morlay, Catherine and Parmentier, Julien and Prelot, B{\'e}n{\'e}dicte and Rossignol, Sylvie and Simon-Masseron, Ang{\'e}lique and Thibault-Starzyk, Fr{\'e}d{\'e}ric} } @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} } @article {133, title = {Cement As a Waste Form for Nuclear Fission Products: The Case of 90 Sr and Its Daughters}, journal = {Environ Sci Technol}, volume = {49}, year = {2015}, month = {Oct-2015}, pages = {13676-83}, abstract = {

One of the main challenges faced by the nuclear industry is the long-term confinement of nuclear waste. Because it is inexpensive and easy to manufacture, cement is the material of choice to store large volumes of radioactive materials, in particular the low-level medium-lived fission products. It is therefore of utmost importance to assess the chemical and structural stability of cement containing radioactive species. Here, we use ab initio calculations based on density functional theory (DFT) to study the effects of (90)Sr insertion and decay in C-S-H (calcium-silicate-hydrate) in order to test the ability of cement to trap and hold this radioactive fission product and to investigate the consequences of its \β-decay on the cement paste structure. We show that (90)Sr is stable when it substitutes the Ca(2+) ions in C-S-H, and so is its daughter nucleus (90)Y after \β-decay. Interestingly, (90)Zr, daughter of (90)Y and final product in the decay sequence, is found to be unstable compared to the bulk phase of the element at zero K but stable when compared to the solvated ion in water. Therefore, cement appears as a suitable waste form for (90)Sr storage.

}, issn = {1520-5851}, doi = {10.1021/acs.est.5b02609}, author = {Dezerald, Lucile and Kohanoff, Jorge J and Alfredo A. Correa and Caro, Alfredo and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Andres Sa{\`u}l} } @article {157, title = {Critical Casimir force between inhomogeneous boundaries}, journal = {EPL (Europhysics Letters)}, volume = {112}, year = {2015}, month = {Dec-2015}, pages = {66004}, abstract = {

To study the critical Casimir force between chemically structured boundaries immersed in a binary mixture at its demixing transition, we consider a strip of Ising spins subject to alternating fixed spin boundary conditions. The system exhibits a boundary induced phase transition as function of the relative amount of up and down boundary spins. This transition is associated with a sign change of the asymptotic force and a diverging correlation length that sets the scale for the crossover between different universal force amplitudes. Using conformal field theory and a mapping to Majorana fermions, we obtain the universal scaling function of this crossover, and the force at short distances.

}, issn = {0295-5075}, doi = {10.1209/0295-5075/112/66004}, author = {Dubail, Jerome and Santachiara, Raoul and Emig, Thorsten} } @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} } @article {644, title = {First-principles prediction of kink-pair activation enthalpy on screw dislocations in bcc transition metals: V, Nb, Ta, Mo, W, and Fe}, journal = {Physical Review B}, volume = {91}, year = {2015}, month = {Mar-09-2015}, pages = { Article Number 094105 }, abstract = {

The atomistic study of kink pairs on screw dislocations in body-centered cubic (bcc) metals is challenging because interatomic potentials in bcc metals still lack accuracy and kink pairs require too many atoms to be modeled by first principles. Here, we circumvent this difficulty using a one-dimensional line tension model whose parameters, namely the line tension and Peierls barrier, are reachable to density functional theory calculations. The model parameterized in V, Nb, Ta, Mo, W, and Fe, is used to study the kink-pair activation enthalpy and spatial extension. Interestingly, we find that the atomistic line tension is more than twice the usual elastic estimates. The calculations also show interesting group tendencies with the line tension and kink-pair width larger in group V than in group VI elements. Finally, the present kink-pair activation energies are shown to compare qualitatively with experimental data and potential origins of quantitative discrepancies are discussed.

}, issn = {1098-0121}, doi = {10.1103/PhysRevB.91.094105}, url = {https://link.aps.org/doi/10.1103/PhysRevB.91.094105}, author = {Dezerald, Lucile and Proville, L. and Ventelon, Lisa and Willaime, F. and Rodney, D.} } @proceedings {335, title = {Hydration Kinetics and Gel Morphology of C-S-H}, 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 = {565-573}, publisher = {American Society of Civil Engineers}, address = {September 21{\textendash}23, 2015, Vienna, AustriaReston, VA}, abstract = {

Calcium-silicate hydrate (C-S-H) is the main binder in cement and concrete. It starts forming from the early stages of cement hydration and it progressively densifies as cement sets. C-S-H nanoscale building blocks form a cohesive gel, whose structure and mechanics are still poorly understood, in spite of its practical importance. Here we review a statistical physics approach recently developed, which allows us to investigate the C-S-H gel formation under the out-of-equilibrium conditions typical of cement hydration. Our approach is based on colloidal particles, precipitating in the pore solution and interacting with effective forces associated to the ionic environment. We present the evolution of the space filling of C-S-H with different particle interactions and compare them with experimental data at different lime concentrations. Moreover, we discuss the structural features of C-S-H in the mesoscale in terms of the scattering intensity. The comparison of our early stage C-S-H structures with small angle neutron scattering (SANS) experiments shows that long range spatial correlations and structural heterogeneties that develop in that early stages of hydration persist also in the hardened paste.

}, doi = {10.1061/978078447934610.1061/9780784479346.069}, author = {Katerina Ioannidou and Enrico Masoero and Pierre E. Levitz and Roland Jean-Marc Pellenq and Emanuela Del Gado}, editor = {Hellmich, Christian and Pichler, Bernhard and Kollegger, Johann} } @article {271, title = {Implicit frictional-contact model for soft particle systems}, journal = {Journal of the Mechanics and Physics of Solids}, volume = {83}, year = {2015}, month = {Oct-2015}, pages = {72 - 87}, abstract = {

We introduce a novel numerical approach for the simulation of soft particles interacting via frictional contacts. This approach is based on an implicit formulation of the Material Point Method, allowing for large particle deformations, combined with the Contact Dynamics method for the treatment of unilateral frictional contacts between particles. This approach is both precise due to the treatment of contacts with no regularization and artificial damping parameters, and robust due to implicit time integration of both bulk degrees of freedom and relative contact velocities at the nodes representing the contact points. By construction, our algorithm is capable of handling arbitrary particle shapes and deformations. We illustrate this approach by two simple 2D examples: a Hertz contact and a rolling particle on an inclined plane. We also investigate the compaction of a packing of circular particles up to a solid fraction well above the jamming limit of hard particles. We find that, for the same level of deformation, the solid fraction in a packing of frictional particles is above that of a packing of frictionless particles as a result of larger particle shape change.

}, issn = {00225096}, doi = {10.1016/j.jmps.2015.06.007}, author = {Saeid Nezamabadi and Farhang Radja{\"\i} and Julien Averseng and Jean-Yves Delenne} } @article {146, title = {Investigating carbon materials nanostructure using image orientation statistics}, journal = {Carbon}, volume = {84}, year = {2015}, month = {Apr-2015}, pages = {160 - 173}, abstract = {

A new characterization method of the lattice fringe images of turbostratic carbons is proposed. This method is based on the computation of their orientation field without explicit detection of fringes. It allows meaningful insights into the material nanostructure and nanotexture at several scales, either qualitatively or quantitatively. The calculation of pairwise spatial statistics of the orientation field at short distance provides measurements of the coherence lengths along any direction, in particular along and orthogonally to the layers. These statistics also allow representing orientation coherence patterns typical of the observed nanostructure. At larger distances, the mean disorientation of the fringes is computed and information about the homogeneity of the sample is obtained. An experimental validation is carried out on various artificial images and an application to the characterization of four bulk turbostratic carbons is provided.

}, issn = {00086223}, doi = {10.1016/j.carbon.2014.11.048}, author = {J. Philippe Da-Costa and Weisbecker, P. and Baptiste Farbos and Jean-Marc Leyssale and G{\'e}rard L. Vignoles and Germain, C.} } @article {184, title = {Ion-specific adsorption and electroosmosis in charged amorphous porous silica}, journal = {Phys. Chem. Chem. Phys.}, volume = {17}, year = {2015}, month = {Oct-14-2015}, pages = {24683 - 24695}, abstract = {

Monovalent and divalent aqueous electrolytes confined in negatively charged porous silica are studied by means of molecular simulations including free energy calculations. Owing to the strong cation adsorption at the surface, surface charge overcompensation (overscreening) occurs which leads to an effective positive surface next to the Stern layer, followed by a negatively charged diffuse layer. A simple Poisson-Boltzmann model in which the single-ion potential of mean force is introduced is shown to capture the most prominent features of ion density profiles near an amorphous silica surface. Nevertheless, due to its mean-field nature, which fails to account for correlations, this simple model does not predict overscreening corresponding to charge inversion at the surface. Such an overscreening drastically affects the transport of confined electrolytes as it leads to flow reversal when subjected to an electric field. A simple continuum theory is shown to capture how the electro-osmotic flow is affected by overscreening and by the apparent enhanced viscosity of the confined electrolytes. Comparison with available experimental data is discussed, as well as the implications of these phenomena for \ζ-potential measurements.

}, issn = {1463-9076}, doi = {10.1039/C5CP03818A}, author = {Hartkamp, Remco and Bertrand Siboulet and Jean-Francois Dufreche and Benoit A. Coasne} } @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} } @article {646, title = {Les mat{\'e}riaux poreux : un domaine scientifique et technologique pluridisciplinaire au futur radieux}, journal = {Mat{\'e}riaux \& Techniques}, volume = {103}, year = {2015}, month = {2015}, pages = {701}, abstract = {

Porous materials cover a broad multidisciplinary scientific and technological domain. They are used in numerous existing and emerging devices and processes related to key societal issues both in environmental protection and for the benefit of the economy. Our choice was to illustrate advances in porous materials through three specific examples: porous materials engineering in the case of organic mesoporous materials prepared from block polymers, modeling and numerical simulation of adsorption of molecular species at the nanoscale and, finally technological applications as thermal insulators.

}, issn = {0032-6895}, doi = {10.1051/mattech/2015050}, url = {http://www.mattech-journal.org/10.1051/mattech/2015050}, author = {Ayral, Andre and Calas-Etienne, Sylvie and Benoit A. Coasne and Deratani, Andr{\'e} and Grande, Daniel and Quemener, Damien and Rossignol, Sylvie} } @article {156, title = {Liquid clustering and capillary pressure in granular media}, journal = {Journal of Fluid Mechanics}, volume = {762}, year = {2015}, month = {Jan-2015}, pages = {Article Number: R5}, abstract = {

By means of extensive lattice Boltzmann simulations, we investigate the process of growth and coalescence of liquid clusters in a granular material as the amount of liquid increases. A homogeneous grain\–liquid mixture is obtained by means of capillary condensation, thus providing meaningful statistics on the liquid distribution inside the granular material. The tensile stress carried by the grains as a function of the amount of condensed liquid reveals four distinct states, with a peak stress occurring at the transition from a primary coalescence process, where the cohesive strength is carried mostly by the grains, to a secondary process governed by the increase of the liquid cluster volumes. We show that the evolution of capillary states is correctly captured by a simple model accounting for the competing effects of the Laplace pressure and grain\–liquid interface.

}, issn = {0022-1120}, doi = {10.1017/jfm.2014.676}, author = {Jean-Yves Delenne and Vincent Richefeu and Farhang Radja{\"\i}} } @article {645, title = {Magnetic nanopantograph in the SrCu 2 (BO 3 ) 2 Shastry{\textendash}Sutherland lattice}, journal = {Proceedings of the National Academy of Sciences}, volume = {112}, year = {2015}, month = {Feb-17-2015}, pages = { 1971-1976}, abstract = {

Magnetic materials having competing, i.e., frustrated, interactions can display magnetism prolific in intricate structures, discrete jumps, plateaus, and exotic spin states with increasing applied magnetic fields. When the associated elastic energy cost is not too expensive, this high potential can be enhanced by the existence of an omnipresent magnetoelastic coupling. Here we report experimental and theoretical evidence of a nonnegligible magnetoelastic coupling in one of these fascinating materials, SrCu2(BO3)(2) (SCBO). First, using pulsed-field transversal and longitudinal magnetostriction measurements we show that its physical dimensions, indeed, mimic closely its unusually rich field-induced magnetism. Second, using density functional-based calculations we find that the driving force behind the magnetoelastic coupling is the CuOCu superexchange angle that, due to the orthogonal Cu2+ dimers acting as pantographs, can shrink significantly (0.44\%) with minute (0.01\%) variations in the lattice parameters. With this original approach we also find a reduction of similar to 10\% in the intradimer exchange integral J, enough to make predictions for the highly magnetized states and the effects of applied pressure on SCBO.

}, issn = {0027-8424}, doi = {10.1073/pnas.1421414112}, url = {http://www.pnas.org/lookup/doi/10.1073/pnas.1421414112}, author = {Guillaume Radtke and Andres Sa{\`u}l and Dabkowska, Hanna A. and Salamon, Myron B. and Jaime, Marcelo} } @article {117, title = {Magnetic nanopantograph in the SrCu2(BO3)2 Shastry{\textendash}Sutherland lattice}, journal = {Proceedings of the National Academy of Sciences}, volume = {112}, year = {2015}, month = {Feb-02-2015}, pages = {1971-1976}, abstract = {

Magnetic materials having competing, i.e., frustrated, interactions can display magnetism prolific in intricate structures, discrete jumps, plateaus, and exotic spin states with increasing applied magnetic fields. When the associated elastic energy cost is not too expensive, this high potential can be enhanced by the existence of an omnipresent magnetoelastic coupling. Here we report experimental and theoretical evidence of a nonnegligible magnetoelastic coupling in one of these fascinating materials, SrCu2(BO3)2 (SCBO). First, using pulsed-field transversal and longitudinal magnetostriction measurements we show that its physical dimensions, indeed, mimic closely its unusually rich field-induced magnetism. Second, using density functional-based calculations we find that the driving force behind the magnetoelastic coupling is the CuOCu^ superexchange angle that, due to the orthogonal Cu2+ dimers acting as pantographs, can shrink significantly (0.44\%) with minute (0.01\%) variations in the lattice parameters. With this original approach we also find a reduction of \∼10\% in the intradimer exchange integral J, enough to make predictions for the highly magnetized states and the effects of applied pressure on SCBO.

}, doi = {10.1073/pnas.1421414112}, author = {Guillaume Radtke and Andres Sa{\`u}l and Dabkowska, Hanna A. and Salamon, Myron B. and Jaime, Marcelo} } @proceedings {330, title = {The Meso-Scale Texture of Cement Hydrate Gels: Out-of-Equilibrium Evolution and Thermodynamic Driving}, journal = {10th International Conference on Mechanics and Physics of Creep, Shrinkage, and Durability of Concrete and Concrete Structures CONCREEP 10}, volume = {CONCREEP 10: MECHANICS AND PHYSICS OF CREEP, SHRINKAGE, AND DURABILITY OF CONCRETE AND CONCRETE STRUCTURES}, year = {2015}, month = {Sep-17-2015}, pages = {34-38}, publisher = {American Society of Civil Engineers}, address = {September 21{\textendash}23, 2015 Vienna, AustriaReston, VA}, abstract = {

By the end of cement hydration calcium-silicate-hydrate (C-S-H) gels extends over tens and hundreds of nanometers. Their complex texture affects directly, and to a large extent, the macroscopic hygrothermal and mechanical behavior of cement. Here we review 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 investigations have unveiled the role, in the C-S-H gels, of nano-scale structural and mechanical heterogeneities that develop due to the the far-from-equilibrium physico-chemical environment in which the material forms. A subtle interplay between the out-of-equilibrium evolution and the effective interactions emerging between the nano-scale units of the gels at different stages of the hydration process ultimately determines the mesoscale texture of cement hydrates and their material properties.

}, doi = {10.1061/978078447934610.1061/9780784479346.005}, author = {Emanuela Del Gado and Katerina Ioannidou and Enrico Masoero 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 {143, title = {Nanoscale elasticity of highly anisotropic pyrocarbons}, journal = {Carbon}, volume = {94}, year = {2015}, month = {Nov-2015}, pages = {285 - 294}, abstract = {

We report on the elastic properties of high-textured laminar pyrocarbons (PyCs) as obtained at the nanoscale using atomistic simulations on realistic models of the rough laminar (RL) PyC, the regenerative laminar (ReL) PyC, and the ReL PyC heat treated at temperatures up to 1700 \°C. The purely longitudinal ( and ) and transverse ( and ) elastic properties of such materials have values of around 50\–75\% of those found for graphite. Conversely, cross longitudinal-transverse properties ( and ) are much larger in PyCs than in graphite (up to around one order of magnitude for ). Our results also show that stiffness decreases with the hydrogen content, that longitudinal properties increase with the extent of graphene domains and decrease with the misorientation of the layers, and that transverse and cross properties significantly increase with the amount of interlayer cross-links present in the materials. Comparison to known experimental data indicates that texture effect at superior scales play an important role in the effective macroscopic elasticity constants. Finally, from a materials perspective and in agreement with the structural evolution, the elastic properties of the ReL PyC evolve with heat treatment towards those of the RL PyC.

}, issn = {00086223}, doi = {10.1016/j.carbon.2015.06.060}, author = {Baptiste Farbos and J. Philippe Da-Costa and G{\'e}rard L. Vignoles and Jean-Marc Leyssale} } @proceedings {351, title = {Numerical simulation of granular media composed with irregular polyhedral particles: effect of particles{\textquoteright} angularity}, journal = {2nd International Conference on Particle-Based Methods - Fundamentals and Applications (Particles)}, volume = {PARTICLE-BASED METHODS II: FUNDAMENTALS AND APPLICATIONS}, year = {2015}, month = {Feb-02-2015}, pages = {222-228}, address = {OCT 26-28 2011 Barcelona, SPAIN}, abstract = {

We use contact dynamic simulations to perform a systematic investigation of the effects of particles shape angularity on mechanicals response in sheared granular ma-terials. The particles are irregular polyhedra with varying numbers of face from spheres to \"double pyramid\" shape with a constant aspect ratio. We study the quasi-static behav-ior, structural and force anisotropies of several packings subjected to triaxial compression. An interesting finding is that the shear strength first increases with angularity up to a maximum value and then saturates as the particles become more angular. Analyzing the anisotropies induced by the angular distributions of contacts and forces orientations, we show that the saturation of the shear strength at higher angularities is a consequence of fall-off of the texture anisotropies compensated by an increase of the tangential force anisotropy. This is attributed to the fact that at higher angularity, particles are bet-ter connected (or surrounded) leading to an increase of friction mobilization in order to achieve the deformation. Moreover, the most angular particles also have very few sides so that, this effect is enhanced by the increase of the proportion of face-side and side-side contacts with angularity.

}, keywords = {angularity, force transmission, Granular Materials, particle shape, texture}, url = {https://hal.archives-ouvertes.fr/hal-01112373}, author = {Emilien Az{\'e}ma and Farhang Radja{\"\i} and Dubois, Fr{\'e}d{\'e}ric}, editor = {Onate, E and Owen, DRJ} } @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 {152, title = {Transient dynamics of a 2D granular pile}, journal = {The European Physical Journal E}, volume = {38}, year = {2015}, month = {May-26-2015}, pages = {Article Number: 47}, abstract = {

We investigate by means of Contact Dynamics simulations the transient dynamics of a 2D granular pile set into motion by applying shear velocity during a short time interval to all particles. The spreading dynamics is directly controlled by the input energy whereas in recent studies of column collapse the dynamics scales with the initial potential energy of the column. As in column collapse, we observe a power-law dependence of the runout distance with respect to the input energy with nontrivial exponents. This suggests that the power-law behavior is a generic feature of granular dynamics, and the values of the exponents reflect the distribution of kinetic energy inside the material. We observe two regimes with different values of the exponents: the low-energy regime reflects the destabilization of the pile by the impact with a runout time independent of the input energy whereas the high-energy regime is governed by the input energy. We show that the evolution of the pile in the high-energy regime can be described by a characteristic decay time and the available energy after the pile is destabilized.

https://static-content.springer.com/image/art\%3A10.1140\%2Fepje\%2Fi2015-15047-x/MediaObjects/10189_2015_133_Figa_HTML.gif
}, issn = {1292-8941}, doi = {10.1140/epje/i2015-15047-x}, author = {Patrick Mutabaruka and Krishna Kumar and Kenichi Soga and Farhang Radja{\"\i} and Jean-Yves Delenne} } @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 {40, title = {Controlling local packing and growth in calcium-silicate-hydrate gels}, journal = {Soft Matter}, volume = {10}, year = {2014}, month = {Oct-2014}, pages = {1121-1133}, abstract = {

We investigate the development of gels under out-of-equilibrium conditions, such as calcium\–silicate\–hydrate (C\–S\–H) gels that form during cement hydration and are the major factor responsible for cement mechanical strength. We propose a new model and numerical approach to follow the gel formation upon precipitation and aggregation of nano-scale colloidal hydrates, whose effective interactions are consistent with forces measured in experiments at fixed lime concentrations. We use Grand Canonical Monte Carlo to mimic precipitation events during Molecular Dynamics simulations, with their rate corresponding to the hydrate production rate set by the chemical environment. Our results display hydrate precipitation curves that indeed reproduce the acceleration and deceleration regime typically observed in experiments and we are able to correctly capture the effect of lime concentration on the hydration kinetics and the gel morphology. Our analysis of the evolution of the gel morphology indicates that the acceleration is related to the formation of an optimal local crystalline packing that allows for large, elongated aggregates to grow and that is controlled by the underlying thermodynamics. The defects produced during precipitation favor branching and gelation that end up controlling the deceleration. The effects on the mechanical properties of C\–S\–H gels are also discussed.

Graphical abstract: Controlling local packing and growth in calcium{\textendash}silicate{\textendash}hydrate gels
}, doi = {10.1039/C3SM52232F}, author = {Katerina Ioannidou and Roland Jean-Marc Pellenq and Emanuela Del Gado} } @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} } @article {275, title = {Initiation of immersed granular avalanches}, journal = {Physical Review E}, volume = {89}, year = {2014}, month = {May-09-2014}, pages = {Article Number: 052203}, abstract = {

By means of coupled molecular dynamics-computational fluid dynamics simulations, we analyze the initiation of avalanches in a granular bed of spherical particles immersed in a viscous fluid and inclined above its angle of repose. In quantitative agreement with experiments, we find that the bed is unstable for a packing fraction below 0.59 but is stabilized above this packing fraction by negative excess pore pressure induced by the effect of dilatancy. From detailed numerical data, we explore the time evolution of shear strain, packing fraction, excess pore pressures, and granular microstructure in this creeplike pressure redistribution regime, and we show that they scale excellently with a characteristic time extracted from a model based on the balance of granular stresses in the presence of a negative excess pressure and its interplay with dilatancy. The cumulative shear strain at failure is found to be ≃ 0.2, in close agreement with the experiments, irrespective of the initial packing fraction and inclination angle. Remarkably, the avalanche is triggered when dilatancy vanishes instantly as a result of fluctuations while the average dilatancy is still positive (expanding bed) with a packing fraction that declines with the initial packing fraction. Another nontrivial feature of this creeplike regime is that, in contrast to dry granular materials, the internal friction angle of the bed at failure is independent of dilatancy but depends on the inclination angle, leading therefore to a nonlinear dependence of the excess pore pressure on the inclination angle. We show that this behavior may be described in terms of the contact network anisotropy, which increases with a nearly constant connectivity and levels off at a value (critical state) that increases with the inclination angle. These features suggest that the behavior of immersed granular materials is controlled not only directly by hydrodynamic forces acting on the particles but also by the influence of the fluid on the granular microstructure.

}, issn = {1539-3755}, doi = {10.1103/PhysRevE.89.052203}, author = {Patrick Mutabaruka and Jean-Yves Delenne and Kenichi Soga and Farhang Radja{\"\i}} } @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} } @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} } @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 {96, title = {Nano-scale mechanics of colloidal C-S-H gels}, journal = {Soft Matter}, volume = {10}, year = {2014}, month = {Jan-21-2014}, pages = {491-499}, type = {Article}, abstract = {

Gels of calcium-silicate-hydrates (C-S-H) are the glue that is largely responsible for the mechanical properties of cement. Despite their practical relevance, their nano-scale structure and mechanics are still mainly unexplored, because of the difficulties in characterizing them in a complex material like cement. We propose a colloidal model to investigate the gel mechanics emerging in the critical range of length-scales from several tens to hundreds of nanometers. We show that the size polydispersity of the hydrates and size-dependent effective interactions can explain the mechanical heterogeneities detected in nano-indentation experiments. We also show how these features control the arising of irreversible structural rearrangements under deformation, which are good candidates as nano-scale mechanisms underlying mechanical aging and slow structural relaxation in the gels.

Graphical abstract: Nano-scale mechanics of colloidal C{\textendash}S{\textendash}H gels
}, issn = {1744-683X}, doi = {10.1039/c3sm51815a}, author = {Enrico Masoero and Emanuela Del Gado and Roland Jean-Marc Pellenq and Sidney Yip and Franz-Josef Ulm} } @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 {91, title = {Role of Silver Nanoparticles in Enhanced Xenon Adsorption Using Silver-Loaded Zeolites}, journal = {Journal of Physical Chemistry C }, volume = {118}, year = {2014}, month = {Oct-06-2014}, pages = {25032-25040}, type = {Article}}, abstract = {
Abstract Image

Molecular simulation is used to unravel the adsorption mechanisms of xenon on Ag-doped ZSM-5 zeolite. We show that silver nanoparticles, which form at the external surface of zeolite crystallites, are responsible for enhanced xenon physisorption at very low pressure. We also propose a simple model of adsorption on such composite materials made up of silver-exchanged zeolites and silver nanoparticles adsorbed at the zeolite surface. This model, which allows predicting the adsorption of other gases without any additional parameters, provides a tool to characterize the amount of reduced silver as well as the silver particle size distribution (in good agreement with transmission electron microscopy images). The presence of a majority of silver nanoparticles is further characterized by means of X-ray diffraction and X-ray Absorption Spectroscopy at the silver K edge.

}, issn = {1932-7447}, doi = {10.1021/jp507590a}, author = {Deliere, Ludovic and Topin, Sylvain and Benoit A. Coasne and Fontaine, Jean-Pierre and De Vito, Sophie and Den Auwer, Christophe and Solari, Pier Lorenzo and Daniel, Cecile and Schuurman, Yves and David Farrusseng} } @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 {276, title = {Some micromechanical aspects of failure in granular materials based on second-order work}, journal = {Comptes Rendus M{\'e}canique}, volume = {342}, year = {2014}, month = {Mar-2014}, pages = {174 - 188}, abstract = {

This paper discusses the notion of failure in a granular assembly by examining the key microstructural mechanisms which are most likely to trigger the nucleation and propagation of instabilities within a granular material. For this purpose, the key variable to predict the occurrence of failure, known as second-order work, is expressed from variables on the grain scale. The local behaviour incidents (where contacts may open or slide), compared to the global response of the assembly, are analysed by two approaches. First, numerical computations made by a discrete element model confirm the microscopic definition of the second-order work. Secondly, a micromechanical model, based on a homogenization procedure, relating the macroscopic behaviour to microscopic ingredients, namely contact planes, points to a close link between the occurrence of failure on the macroscopic scale as well as on the contact planes.

}, issn = {16310721}, doi = {10.1016/j.crme.2014.01.006}, author = {Fran{\c c}ois Nicot and Hadda, Nejib and Sibille, Luc and Farhang Radja{\"\i} and Hicher, Pierre-Yves and Darve, F{\'e}lix} } @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 {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 {95, title = {Adsorption, intrusion and freezing in porous silica: the view from the nanoscale}, journal = {Chemical Society Reviews}, volume = {42}, year = {2013}, month = {Jan-24-2013}, pages = {4141-4171}, type = {Review}, abstract = {

This review presents the state of the art of molecular simulation and theory of adsorption, intrusion and freezing in porous silica. Both silica pores of a simple geometry and disordered porous silicas which exhibit morphological and topological disorders are considered. We provide a brief description of the numerical models of porous silicas available in the literature and present the most common molecular simulation and theoretical methods. Adsorption in regular and irregular pores is discussed in the light of classical theories of adsorption and capillary condensation in pores. We also present the different evaporation mechanisms for disordered systems: pore blocking and cavitation. The criticality of fluids confined in pores, which is still the matter of debate, is then discussed. We review theoretical results for intrusion/extrusion and freezing in silica pores and discuss the validity of classical approaches such as the Washburn-Laplace equation and Gibbs-Thomson equation to describe the thermodynamics of intrusion and in-pore freezing. The validity of the most widely used characterization techniques is then discussed. We report some concluding remarks and suggest directions for future work.

Graphical abstract: Adsorption, intrusion and freezing in porous silica: the view from the nanoscale

}, issn = {0306-0012}, doi = {10.1039/c2cs35384a}, author = {Benoit A. Coasne and Anne Galarneau and Roland Jean-Marc Pellenq and Di Renzo, Francesco} } @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 {24, title = {Adsorption of Volatile Organic Compounds in pure silica CHA, *BEA, MFI and STT-type zeolites}, journal = {Microp. Mesop. Mater.}, volume = {173}, year = {2013}, month = {Jun-2013}, pages = {147{\textendash}154}, abstract = {

Four pure silica zeolites, chabazite (CHA-structure type) and SSZ-23 (STT-structure type) with cage-like structure and silicalite-1 (MFI-structure type) and beta (\∗BEA-structure type) with channel structure, were synthesized and fully characterized. Their sorption properties were examined using gravimetric method combined with Grand Canonical Monte Carlo simulations (GCMC). Of particular interest is the large difference in the adsorption rates of n-hexane, p-xylene and acetone observed for these zeosils at 25, 75 and 150\ \°C. As expected, in most cases, a decrease in the adsorption capacity is observed with increasing the molar volume of the used probe molecule and the temperature. An exception is observed for the pure silica CHA-type zeolite due to its small pore size which prevents molecules from entering its porosity. However, at higher temperature, the window size widens slightly and allows n-hexane and acetone, which have kinetic diameter close to the pore opening, to enter easily in chabazite. As a result, for this zeosil, an increase in the adsorption capacity compared to that obtained at 25\ \°C is observed. All these zeosils are promising for technological uses in car exhaust gas decontamination.

Image for unlabelled figure

}, doi = {10.1016/j.micromeso.2013.02.009}, author = {A. F. Cosseron and T. J. Daou and L. Tzanis and H. Nouali and I. Deroche and Benoit A. Coasne and V. Tchaber and J. Patarin} } @proceedings {365, title = {AIP Conference Proceedings A multiscale description of failure in granular materials}, 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 = {585-588}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

This paper presents conditions of initiation and development of failure in granular materials through a twodimensional discrete element model. General condition for the effective development of failure and its physical characteristics are recalled. Then relation between failure and the second order work expressed in terms of microscopic variables is discussed. Eventually, correspondence between a localized mode of failure marked with shear band patterns and space distribution of negative values of microscopic second-order work is investigated.

}, doi = {10.1063/1.4811999}, author = {Hadda, Nejib and Fran{\c c}ois Nicot and Sibille, Luc and Farhang Radja{\"\i} and Tordesillas, Antoinette and Darve, F{\'e}lix}, editor = {Yu, A and Dong, K and Yang, R} } @proceedings {366, title = {AIP Conference ProceedingsTumbling sandpiles in a fluid}, 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-2013}, pages = {662-665}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

By means of contact dynamics simulations interfaced with computational fluid dynamics, we analyze the effect of a suspending fluid on the dynamics of collapse and spread of a granular column. We find that the runout distance increases as a power law with the aspect ratio of the column and, for a given aspect ratio, it may be the same in the grain-inertial and fluid-inertial regimes but with considerably longer duration in the latter case. We show that, in both viscous and fluid-inertial regimes, this behavior results from compensation between two effects of the fluid: 1) reduction of the kinetic energy during collapse and 2) enhancement of the flow by lubrication during spread.

}, doi = {10.1063/1.4812018}, author = {Farhang Radja{\"\i} and Vincent Topin and Perales, F. and Yann Monerie}, editor = {Yu, A and Dong, K and Yang, R} } @proceedings {367, title = {A benchmark for particle shape dependence}, 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 = {883-886}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

Particle shape is a major parameter for the space-filling and strength properties of granular materials. For a systematic investigation of shape effect, a numerical benchmark test was set up within a collaborative group using different numerical methods and particles of various shape characteristics such as elongation, angularity and nonconvexity. Extensive 2D shear simulations were performed in this framework and the shear strength and packing fraction were compared for different shapes. We show that the results may be analyzed in terms of a low-order shape parameter \η describing the degree of distortion from a perfectly circular shape. In particular, the shear strength is an increasing function of \η with nearly the same trend for all shapes, the differences being of second order compared to \η. We also observe a nontrivial behavior of packing fraction which, for all our simulated shapes, increases with \η from the random close packing fraction for disks, reaches a peak considerably higher than that for disks, and subsequently declines as \η is further increased. Finally, the analysis of contact forces for the same value of \η leads to very similar statistics regardless of our specific particle shapes.

}, doi = {10.1063/1.4812073}, author = {Gael Combe and C{\'e}cile Nouguier-Lehon and Emilien Az{\'e}ma and Krzysztof Szarf and Baptiste Saint-Cyr and Marie Chaze and Farhang Radja{\"\i} and Pascal Villard and Jean-Yves Delenne and Vincent Richefeu and Philippe Sornay and Charles Voivret and CEGEO Group}, editor = {Yu, A and Dong, K and Yang, R} } @proceedings {369, title = {Capillary states of granular materials in the funicular state}, 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 = {1023-1026}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

Using a multi-phase lattice Boltzmann model, we investigate the capillary states of a 2D granular packing gradually saturated by condensation from a homogeneously injected vapor phase. The internal stresses induced by surface tension and Laplace pressure are directly calculated from the forces acting on the grains with increasing amount of liquid. The evolution of cohesive strength with the amount of liquid reveals four different states reflecting the connectivity of the liquid phase and local grain environments. It increases in the pendular state, characterized by binary liquid bridges holding the grains together, and within the funicular state with an increasing number of liquid clusters connected to several grains. Beyond 40\% of saturation, the cohesive strength falls off due to a decreasing Laplace pressure of liquid clusters.

}, doi = {10.1063/1.4812108}, author = {Jean-Yves Delenne and Vincent Richefeu and Farhang Radja{\"\i}}, editor = {Yu, A and Dong, K and Yang, R} } @article {281, title = {Cohesive granular materials composed of nonconvex particles}, journal = {Physical Review E}, volume = {87}, year = {2013}, month = {May-28-2013}, pages = {Article Number: 052207}, abstract = {

The macroscopic cohesion of granular materials made up of sticky particles depends on the particle shapes. We address this issue by performing contact dynamics simulations of 2D packings of nonconvex aggregates. We find that the macroscopic cohesion is strongly dependent on the strain and stress inhomogeneities developing inside the material. The largest cohesion is obtained for nearly homogeneous deformation at the beginning of unconfined axial compression and it evolves linearly with nonconvexity. Interestingly, the aggregates in a sheared packing tend to form more contacts with fewer neighboring aggregates as the degree of nonconvexity increases. We also find that shearing leads either to an isotropic distribution of tensile contacts or to the same privileged direction as that of compressive contacts.

}, issn = {1539-3755}, doi = {10.1103/PhysRevE.87.052207}, author = {Baptiste Saint-Cyr and Farhang Radja{\"\i} and Jean-Yves Delenne and Philippe Sornay} } @proceedings {368, title = {Comparison of the effects of rolling resistance and angularity in sheared granular media}, 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-2013}, pages = {891-894}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

In this paper, we compare the effect of rolling resistance at the contacts in granular systems composed of disks with the effect of angularity in granular systems composed of regular polygonal particles. For this purpose, we use contact dynamics simulations. By means of a simple shear numerical device, we investigate the mechanical behavior of these materials in the steady state in terms of shear strength, solid fraction, force and fabric anisotropies, and probability distribution of contact forces. We find that, based on the energy dissipation associated with relative rotation between two particles in contact, the effect of rolling resistance can explicitly be identified with that of the number of sides in a regular polygonal particle. This finding supports the use of rolling resistance as a shape parameter accounting for particle angularity and shows unambiguously that one of the main influencing factors behind the mechanical behavior of granular systems composed of noncircular particles is the partial hindrance of rotations as a result of angular particle shape.

}, keywords = {angularity, anisotropy, force distribution, Granular material, rolling resistance, Shear strength, solid fraction}, url = {https://hal.archives-ouvertes.fr/hal-00842799}, author = {Estrada, Nicolas and Emilien Az{\'e}ma and Farhang Radja{\"\i} and Taboada, Alfredo}, editor = {Yu, A and Dong, K and Yang, R} } @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 {279, title = {Nano-mechanical properties of starch and gluten biopolymers from atomic force microscopy}, journal = {European Polymer Journal}, volume = {49}, year = {2013}, month = {Dec-2013}, pages = {3788 - 3795}, abstract = {

An original method based on atomic force microscopy (AFM) in contact mode was developed to abrade progressively the surface of tablets made of starch or gluten polymers isolated from wheat. The volume of the material removed by the tip was estimated from the analysis of successive topographic images of the surface, and the shear force was measured by keeping a constant normal force. Our data together with a simple tribological model provide clear evidence for a higher hardness and shear strength of starch compared to gluten. Gluten appears to have mechanical properties close to soft materials, such as talc, whereas starch displays higher hardness close to calcite. Our results are in a better agreement with structural properties of gluten (complex protein network) and starch (granular and semi-cristalline structure) than earlier studies by micro-indentation. This work shows that the AFM scratching method is relevant for the characterization of any polymer surface, in particular in application to materials made of different polymers at the nano-scale.

Graphical abstract

Unlabelled figure
}, issn = {00143057}, doi = {10.1016/j.eurpolymj.2013.08.024}, author = {Chichti, Emna and George, Matthieu and Jean-Yves Delenne and Farhang Radja{\"\i} and Val{\'e}rie Lullien-Pellerina} } @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} } @article {280, title = {Packings of irregular polyhedral particles: Strength, structure, and effects of angularity}, journal = {Physical Review E}, volume = {8713}, year = {2013}, month = {Jun-17-2013}, pages = {Article Number: 062203}, abstract = {

We present a systematic numerical investigation of the shear strength and structure of granular packings composed of irregular polyhedral particles. The angularity of the particles is varied by increasing the number of faces from 8 (octahedronlike shape) to 596. We find that the shear strength increases with angularity up to a maximum value and saturates as the particles become more angular (below 46 faces). At the same time, the packing fraction increases to a peak value but declines for more angular particles. We analyze the connectivity and anisotropy of the microstructure by considering both the contacts and branch vectors joining particle centers. The increase of the shear strength with angularity is shown to be due to a net increase of the fabric and force anisotropies but at higher particle angularity a rapid falloff of the fabric anisotropy is compensated by an increase of force anisotropy, leading thus to the saturation of shear strength.

}, issn = {1539-3755}, doi = {10.1103/PhysRevE.87.062203}, author = {Emilien Az{\'e}ma and Farhang Radja{\"\i} and Dubois, Fr{\'e}d{\'e}ric} } @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 {282, title = {Rheology of three-dimensional packings of aggregates: Microstructure and effects of nonconvexity}, journal = {Physical Review E}, volume = {87}, year = {2013}, month = {May-22-2013}, pages = {Article Number: 052205}, abstract = {

We use 3D contact dynamics simulations to analyze the rheological properties of granular materials composed of rigid aggregates. The aggregates are made from four overlapping spheres and described by a nonconvexity parameter depending on the relative positions of the spheres. The macroscopic and microstructural properties of several sheared packings are analyzed as a function of the degree of nonconvexity of the aggregates. We find that the internal angle of friction increases with nonconvexity. In contrast, the packing fraction increases first to a maximum value but declines as nonconvexity further increases. At high level of nonconvexity, the packings are looser but show a higher shear strength. At the microscopic scale, the fabric and force anisotropy, as well as friction mobilization are enhanced by multiple contacts between aggregates and interlocking, revealing thus the mechanical and geometrical origins of shear strength.

}, issn = {1539-3755}, doi = {10.1103/PhysRevE.87.052205}, author = {Emilien Az{\'e}ma and Farhang Radja{\"\i} and Baptiste Saint-Cyr and Jean-Yves Delenne and Philippe Sornay} } @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} } @proceedings {362, title = {Shear strength, force distributions and friction mobilization in sheared packings composed of angular 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 = {2013}, pages = {511-514}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

In this paper, we explore the effect of particle shape angularity on the mechanical behavior of sheared granular packings. A first series of contact dynamics simulations is performed in 2D with regular polygons with an increasing number of sides ranging from 3 (triangles) to 60. Then, in order to approach \“idealized\” angular particles, a second series of simulations is performed in 3D with irregular polyhedra with the number of faces ranging from 8 (octahedron-like) to 596. A counterintuitive finding is that the shear strength increases with angularity up to a maximum value and saturates as the particles become more angular (below 6 sides in 2D and 46 faces in 3D). A micromechanical analysis of force and contact orientations, all enhanced by face-face and face-side contacts, reveals that this increase is due to an increase of both contact and force anisotropies, and the saturation for higher angularities is a consequence of a rapid fall-off of the contact and normal force anisotropies compensated by an increase of the tangential force anisotropy.

}, doi = {10.1063/1.4811980}, author = {Emilien Az{\'e}ma and Estrada, Nicolas and Farhang Radja{\"\i}}, editor = {Yu, A and Dong, K and Yang, R} } @article {216, title = {Water self-diffusion at the surface of silica glasses: effect of hydrophilic to hydrophobic transition}, journal = {Molecular Physics}, volume = {111}, year = {2013}, month = {Nov-2013}, pages = {3410 - 3417}, abstract = {

We study water dynamics at a silica aqueous interface. Both hydrophilic (hydroxylated) surfaces and hydrophobic surfaces (dehydroxylated upon irradiation) have been generated from atomistic simulations. A new method for the calculation of the normal self-diffusion coefficients based on the calculation of mean first passage times is proposed. It uses the Smoluchowski theory of Brownian motion and it takes proper account of the layering of the molecules. In the case of parallel self-diffusion coefficients, a decrease is found compared to the bulk values. It can be described in terms of hydrodynamic boundary conditions induced by the surface confinement. This hydrodynamic explanation is not enough to interpret the case of normal self-diffusion coefficients for which an important diminution is found. Normal self-diffusion coefficients appear to depend strongly on the hydrophilicity of the surface. They tend towards their bulk value only at long distances from the surfaces. The first layer of water molecules is found to be partially adsorbed.

}, issn = {0026-8976}, doi = {10.1080/00268976.2013.861084}, author = {Bertrand Siboulet and Molina, J. and Benoit A. Coasne and Turq, P. and Jean-Francois Dufreche} } @proceedings {350, title = {Effect of Particle Shape non-Convexity on the Rheology of Granular Media : 3D Contact Dynamics Simulations}, journal = {2nd International Conference on Particle-Based Methods - Fundamentals and Applications (Particles)}, volume = {PARTICLE-BASED METHODS II: FUNDAMENTALS AND APPLICATIONS}, year = {2012}, month = {Apr-10-2012}, pages = {427-434}, address = {OCT 26-28 2011 Barcelona, SPAIN}, abstract = {

We analyze the effect of particle shape non-convexity on the quasi-static behavior of granular materials by means of contact dynamics simulations. The particles are regular aggregates of four overlapping spheres described by a nonconvexity parameter depending on the relative positions of the particles. Several packings are first submitted to isotropic compression without friction. We find that, as in 2D, the solid fraction of isotropic packings increases with non-convexity up to a maximum value and then declines to be nearly equal to that of a packing composed of only spheres. It is also remarkable that the coordination number increases quickly and saturates so that the packings composed of grains with a high level of nonconvexity are looser but more strongly connected. Then, the quasi-static behavior, structural and force anisotropies are analyzed by subjecting each packing to a triaxial compression. We find that the shear strength increases with non-convexity. We show that this increase results from the presence of multiple contacts between trimers leading to enhanced frictional interlocking.

}, keywords = {force transmission, Granular Materials, non-convexity, particle shape, texture}, url = {https://hal.archives-ouvertes.fr/hal-00686453}, author = {Baptiste Saint-Cyr and Emilien Az{\'e}ma and Jean-Yves Delenne and Farhang Radja{\"\i} and Philippe Sornay}, editor = {Onate, E and Owen, DRJ} } @article {308, title = {Fabric evolution and accessible geometrical states in granular materials}, journal = {Granular Matter}, volume = {14}, year = {2012}, month = {Mar-02-2012}, pages = {259 - 264}, abstract = {

We analyze the geometrical states of granular materials by means of a fabric tensor involving the coordination number and fabric anisotropy as the lowest-order descriptors of the contact network. In particular, we show that the fabric states in this representation are constrained by steric exclusions and the condition of mechanical equilibrium required in the quasi-static limit. A simple model, supported by numerical data, allows us to characterize the range of accessible fabric states and the joint evolution of fabric parameters. The critical state in this framework appears as a jammed state in the sense of a saturation of contact gain and loss along the principal strain-rate directions.

}, issn = {1434-5021}, doi = {10.1007/s10035-012-0321-8}, author = {Farhang Radja{\"\i} and Jean-Yves Delenne and Emilien Az{\'e}ma and St{\'e}phane Roux} } @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 {303, title = {Nanochemomechanical assessment of shale: a coupled WDS-indentation analysis}, journal = {Acta Geotechnica}, volume = {7}, year = {2012}, month = {Dec-2012}, pages = {271 - 295}, abstract = {

Establishing the links between the composition, microstructure and mechanics of shale continues to be a formidable challenge for the geomechanics community. In this study, a robust methodology is implemented to access the in situ chemomechanics of this sedimentary rock at micrometer length scales. Massive grids of coupled wave dispersive spectroscopy (WDS) and instrumented indentation experiments were performed over representative material surfaces to accommodate the highly heterogeneous composition and microstructure of shale. The extensive datasets of compositional and mechanical properties were analyzed using multi-variate clustering statistics to determine the attributes of active phases present in shale at microscales. Our chemomechanical analysis confirmed that the porous clay (PC) mechanical phase inferred by statistical indentation corresponds to the clay mineral phase defined strictly on chemical grounds. The characteristic stiffness and hardness behaviors of the PC are realized spatially in regions removed from silt inclusions of quartz and feldspar. At the microscale shared by indentation and WDS experiments, a consistent chemomechanical signature for shale emerges in which the heterogeneities of the PC are captured by the standard deviations of indentation properties and concentrations of chemical elements. However, these local behaviors are of second order compared to the global trend observed for mean mechanical properties and the clay packing density, which synthesizes the relative volumes of clay and nanoporosity in the material. The coupled statistical indentation and WDS technique represents a viable approach to characterize the chemomechanics of shale and other natural porous composites at a consistent scale below the macroscopic level.

}, issn = {1861-1125}, doi = {10.1007/s11440-012-0185-4}, author = {Deirieh, A. and J. Alberto Ortega and Franz-Josef Ulm and Younane N. Abousleiman} } @article {48, title = {Nanostructure and nanomechanics of cement: polydisperse colloidal packing}, journal = {Physical review letters}, volume = {109}, year = {2012}, month = {Oct-10-2012}, pages = { Article Number: 155503}, abstract = {

Cement setting and cohesion are governed by the precipitation and growth of calcium-silicate-hydrate, through a complex evolution of microstructure. A colloidal model to describe nucleation, packing, and rigidity of calcium-silicate-hydrate aggregates is proposed. Polydispersity and particle size dependent cohesion strength combine to produce a spectrum of packing fractions and of corresponding elastic properties that can be tested against nanoindentation experiments. Implications regarding plastic deformations and reconciling current structural characterizations are discussed.

Figure

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}, doi = {10.1103/PhysRevLett.109.155503}, author = {Enrico Masoero and Emanuela Del Gado and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Sidney Yip} } @article {307, title = {Particle shape dependence in 2D granular media}, journal = {EPL (Europhysics Letters)}, volume = {98}, year = {2012}, month = {Apr-20-2012}, pages = {Article Number: 44008}, abstract = {

Particle shape is a key to the space-filling and strength properties of granular matter. We consider a shape parameter

describing the degree of distortion from a perfectly spherical shape. Encompassing most specific shape characteristics such as elongation, angularity and non-convexity, is a low-order but generic parameter that we used in a numerical benchmark test for a systematic investigation of shape dependence in sheared granular packings composed of particles of different shapes. We find that the shear strength is an increasing function of with nearly the same trend for all shapes, the differences appearing thus to be of second order compared to . We also observe a non-trivial behavior of packing fraction which, for all our simulated shapes, increases with from the random close packing fraction for disks, reaches a peak considerably higher than that for disks, and subsequently declines as is further increased. These findings suggest that a low-order description of particle shape accounts for the principal trends of packing fraction and shear strength. Hence, the effect of second-order shape parameters may be investigated by considering different shapes at the same level of .

}, issn = {0295-5075}, doi = {10.1209/0295-5075/98/44008}, author = {Baptiste Saint-Cyr and Krzysztof Szarf and Charles Voivret and Emilien Az{\'e}ma and Vincent Richefeu and Jean-Yves Delenne and Gael Combe and C{\'e}cile Nouguier-Lehon and Pascal Villard and Philippe Sornay and Marie Chaze and Farhang Radja{\"\i}} } @article {295, title = {Tensile strength and fracture of cemented granular aggregates}, journal = {The European Physical Journal E}, volume = {35}, year = {2012}, month = {Nov-2012}, pages = { Article Number: 117}, abstract = {

Cemented granular aggregates include a broad class of geomaterials such as sedimentary rocks and some biomaterials such as the wheat endosperm. We present a 3D lattice element method for the simulation of such materials, modeled as a jammed assembly of particles bound together by a matrix partially filling the interstitial space. From extensive simulation data, we analyze the mechanical properties of aggregates subjected to tensile loading as a function of matrix volume fraction and particle-matrix adhesion. We observe a linear elastic behavior followed by a brutal failure along a fracture surface. The effective stiffness before failure increases almost linearly with the matrix volume fraction. We show that the tensile strength of the aggregates increases with both the increasing tensile strength at the particle-matrix interface and decreasing stress concentration as a function of matrix volume fraction. The proportion of broken bonds in the particle phase reveals a range of values of the particle-matrix adhesion and matrix volume fraction for which the cracks bypass the particles and hence no particle damage occurs. This limit is shown to depend on the relative toughness of the particle-matrix interface with respect to the particles.

}, issn = {1292-8941}, doi = {10.1140/epje/i2012-12117-7}, author = {Rafik Aff{\`e}s and Jean-Yves Delenne and Yann Monerie and Farhang Radja{\"\i} and Vincent Topin} } @article {55, title = {Understanding and Controlling the Reactivity of the Calcium Silicate phases from First Principles}, journal = {Chemistry of Materials}, volume = {24}, year = {2012}, month = {Apr-10-2012}, pages = {1262{\textendash}1267}, abstract = {
Abstract Image

First principles calculations are employed to provide a fundamental understanding of the relationship between the reactivity of synthetic calcium silicate phases and their electronic structure. Our aim is to shed light on the wide range of hydration kinetics observed in different phases of calcium silicate. For example, while the dicalcium silicate (Ca2SiO4) phase slowly reacts with water, the tricalcium silicate (Ca3SiO5) shows much faster hydration kinetics. We show that the high reactivity of Ca3SiO5 is mainly related to the reactive sites around its more ionic oxygen atoms. Ca2SiO4 does not contain these types of oxygen atoms, although experiments suggest that impurities may play a role in changing the reactivity of these materials. We analyze the electronic structure of a wide range of possible substitutions in both Ca3SiO5 and Ca2SiO4 and show that while the influence of different types of impurities on structural properties is similar, their effect on reactivity is very different. Our calculations suggest that the variation of electronic structure is mainly related to the formation of new hybridized orbitals and the charge exchange between the impurity atoms and the bulk material. The charge localization upon introducing impurities is quantified to predict candidate substitutions that could increase the reactivity of Ca2SiO4, which would broaden the applicability of this lower temperature and thus less costly and energetically less demanding phase.

}, doi = {10.1021/cm203127m}, author = {Engin Durgun and Hegoi Manzano and Roland Jean-Marc Pellenq and Jeffrey C Grossman} } @proceedings {356, title = {Compressive strength of an unsaturated granular material during cementation}, journal = {Symposium on Science and Technology of Powders and Sintered Materials (STPMF 2009)}, volume = {POWDER TECHNOLOGY}, year = {2011}, month = {Mar-25-2011}, pages = {308 - 311}, address = {MAY 25-27 2009 Montpellier, FRANCE}, abstract = {

The cohesive behaviour of unsaturated granular materials is due to the presence of cohesive bonds between grains. These bonds can have various physico-chemical characteristics and may evolve with environmental conditions. We study the case of a granular material partially saturated by an aqueous solution. The bonds are thus initially of capillary type and the mechanical strength is weak. At low relative humidity, the phase change of water involves crystallization of the solute at the contact points between grains, generating thus solid bonds. The mechanical strength of the material is then enhanced. An experimental study of the evolution of the mechanical strength during crystallization of the solute shows clearly the transition from capillary regime to cemented regime. This transition is not correlated with the mass of the crystallized solute, but rather with the residual degree of saturation. This behavior is analyzed here in the light of discrete element simulations. We introduce a local cohesion law that accounts for transition from capillary to cemented bonding. This law is formulated in terms of the degree of crystallization as a result of the evaporation of water at the boundary of the sample. The cohesion of the packing is initially of capillary type. A crystallization front then spreads from the sample boundaries to the center of the sample, and the strength increases as a result. Uniaxial compression allows us to determine the strength at different times. The numerical strength agrees well with the experimental data, and reveals strength enhancement as the solute crystallizes, as well as the transition from capillary to cementation regime.

}, issn = {00325910}, doi = {10.1016/j.powtec.2010.08.021}, author = {Jean-Yves Delenne and Souli{\'e}, Fabien and Moulay Sa{\"\i}d El Youssoufi and Farhang Radja{\"\i}} } @article {316, title = {From liquid to solid bonding in cohesive granular media}, journal = {Mechanics of Materials}, volume = {43}, year = {2011}, month = {Oct-2011}, pages = {529 - 537}, abstract = {

We study the transition of a granular packing from liquid to solid bonding in the course of drying. The particles are initially wetted by a liquid brine and the cohesion of the packing is ensured by capillary forces, but the crystallization of the solute transforms the liquid bonds into partially cemented bonds. This transition is evidenced experimentally by measuring the compressive strength of the samples at regular intervals of times. Our experimental data reveal three regimes: (1) Up to a critical degree of saturation, no solid bonds are formed and the cohesion remains practically constant; (2) The onset of cementation occurs at the surface and a front spreads towards the center of the sample with a nonlinear increase of the cohesion; (3) All bonds are partially cemented when the cementation front reaches the center of the sample, but the cohesion increases rapidly due to the strengthening of cemented bonds. We introduce a model based on a parametric cohesion law at the bonds and a bond crystallization parameter. This model predicts correctly the phase transition and the relation between microscopic and macroscopic cohesion.

Fig. 1. (a) Photograph of the sample in the process of drying; (b) The press used for{\textellipsis}

Fig. 2. Compressive yield stress σY, normalized by the yield stress σLY due only to{\textellipsis}

Fig. 3. Photograph of a partially dried sample in the second regime

Fig. 4. Schematic representation of the evolution of bridge: from a liquid to a solid{\textellipsis}

Fig. 5. Evolution of the global crystallization index with time; solid line:{\textellipsis}

Fig. 6. The parametric adhesion law

}, issn = {01676636}, doi = {10.1016/j.mechmat.2011.06.008}, author = {Jean-Yves Delenne and Souli{\'e}, Fabien and Moulay Sa{\"\i}d El Youssoufi and Farhang Radja{\"\i}} } @article {291, title = {Impact of Chemical Impurities on the Crystalline Cement Clinker Phases Determined by Atomistic Simulations}, journal = {Crystal Growth \& Design}, volume = {11}, year = {2011}, month = {Jul-2011}, pages = {2964 - 2972}, abstract = {
Abstract Image

The presence of chemical substitutions is believed to play a crucial role in the hydration reactions, structure, and elastic properties of cement clinker phases. Hence, substitutions are of great technological interest, as more efficient production of cement clinkers would result in a reduction of CO2 emissions, as well as possible economic benefits. Here we use a combination of classical and quantum mechanical simulation methods to study the detailed physicochemical changes of the clinker phases alite (Ca3SiO5) and belite (Ca2SiO4) when Mg2+, Al3+ and Fe3+ guest ions are incorporated into their structure. Using classical force field methods, we considered random substitutions among possible sites and different compositions in order to identify the preferential substitution sites on the crystalline structures. Then, the resulting structural changes that take place to accommodate the guest ions are investigated and discussed in detail. Using quantum mechanical density functional theory calculations the electronic structure of representative configurations has been computed to determine the potential impact of impurities on the reactivity.

}, issn = {1528-7483}, doi = {10.1021/cg200212c}, author = {Hegoi Manzano and Engin Durgun and Mohammad Javad Abdolhosseini Qomi and Franz-Josef Ulm and Roland Jean-Marc Pellenq and Jeffrey C Grossman} } @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} } @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} } @article {315, title = {Rheology of granular materials composed of nonconvex particles}, journal = {Physical Review E}, volume = {84}, year = {2011}, month = {Oct-10-2011}, pages = {Article Number: 041302 Part: 1 }, abstract = {

By means of contact dynamics simulations, we investigate the shear strength and internal structure of granular materials composed of two-dimensional nonconvex aggregates. We find that the packing fraction first grows as the nonconvexity is increased but declines at higher nonconvexity. This unmonotonic dependence reflects the competing effects of pore size reduction between convex borders of aggregates and gain in porosity at the nonconvex borders that are captured in a simple model fitting nicely the simulation data both in the isotropic and sheared packings. On the other hand, the internal angle of friction increases linearly with nonconvexity and saturates to a value independent of nonconvexity. We show that fabric anisotropy, force anisotropy, and friction mobilization, all enhanced by multiple contacts between aggregates, govern the observed increase of shear strength and its saturation with increasing nonconvexity. The main effect of interlocking is to dislocate frictional dissipation from the locked double and triple contacts between aggregates to the simple contacts between clusters of aggregates. This self-organization of particle motions allows the packing to keep a constant shear strength at high nonconvexity.

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}, issn = {1539-3755}, doi = {10.1103/PhysRevE.84.041302}, author = {Baptiste Saint-Cyr and Jean-Yves Delenne and Charles Voivret and Farhang Radja{\"\i} and Philippe Sornay} } @proceedings {355, title = {Stress fields in granular solids: Effect of composition}, journal = {Symposium on Science and Technology of Powders and Sintered Materials (STPMF 2009)}, volume = {POWDER TECHNOLOGY}, year = {2011}, month = {Mar-25-2011}, pages = {568 - 573}, address = {MAY 25-27 2009 Montpellier, FRANCE}, abstract = {

We use the lattice element method to investigate stress fields at the sub-particle scale in granular solids composed of particles embedded in a cementing matrix. The stress distributions are found to be similar in 2D and 3D samples subjected to vertical loading with free lateral boundaries. We find that the number of strong forces falls off exponentially at high particle volume fractions where a percolating network of jammed particles occurs. The influence of the matrix volume fraction and particle/matrix stiffness ratio with respect to stress distribution is analyzed in 2D and 3D. We show that both decreasing the matrix volume fraction and increasing the stiffness ratio lead to increasingly broader distributions within a limit beyond which the distribution is independent of one or both of these parameters.

}, issn = {00325910}, doi = {10.1016/j.powtec.2010.08.060}, author = {Vincent Topin and Farhang Radja{\"\i} and Jean-Yves Delenne} }