@article {656, title = {Virus-templated Pt{\textendash}Ni(OH)2 nanonetworks for enhanced electrocatalytic reduction of water}, journal = {Nano Energy}, volume = {58}, year = {2019}, month = {Avr-2019}, pages = {167 - 174}, abstract = {

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

}, issn = {22112855}, doi = {10.1016/j.nanoen.2018.12.083}, url = {https://linkinghub.elsevier.com/retrieve/pii/S2211285518309960}, author = {Records, William C. and Yoon, Youngmin and Ohmura, Jacqueline F. and Chanut, Nicolas and Belcher, Angela M.} } @article {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 {630, title = {Mesoscale structure, mechanics, and transport properties of source rocks{\textquoteright} organic pore networks}, journal = {Proceedings of the National Academy of Sciences}, volume = {115}, year = {2018}, month = {Dec-04-2018}, pages = {12365-12370}, abstract = {

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

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

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

}, issn = {14668564}, doi = {10.1016/j.ifset.2017.09.015}, url = {https://linkinghub.elsevier.com/retrieve/pii/S1466856417302230}, author = {Barnabe, M. and Blanc, Nicolas and Chabin, T. and Jean-Yves Delenne and Duri, A. and Frank, Xavier and Hugouvieux, V. and Lutton, E. and Mabille, F. and Saeid Nezamabadi and Perrot, N. and Farhang Radja{\"\i} and Ruiz, T. and Tonda, A.} } @article {570, title = {Poroelasticity of Methane-Loaded Mature and Immature Kerogen from Molecular Simulations}, journal = {Langmuir}, volume = {34}, year = {2018}, month = {Nov-13-2018}, pages = {13766 - 13780}, abstract = {

While hydrocarbon expulsion from kerogen is certainly the key step in shale oil/gas recovery, the poromechanical couplings governing this desorption process, taking place under a significant pressure gradient, are still poorly understood. Especially, most molecular simulation investigations of hydrocarbon adsorption and transport in kerogen have so far been performed under the rigid matrix approximation, implying that the pore space is independent of pressure, temperature, and fluid loading, or in other words, neglecting poromechanics. Here, using two hydrogenated porous carbon models as proxies for immature and overmature kerogen, that is, highly aliphatic hydrogen-rich vs highly aromatic hydrogen-poor models, we perform an extensive molecular-dynamics-based investigation of the evolution of the poroelastic properties of those matrices with respect to temperature, external pressure, and methane loading as a prototype alkane molecule. The rigid matrix approximation is shown to hold reasonably well for overmature kerogen even though accounting for flexibility has allowed us to observe the well-known small volume contraction at low fluid loading and temperature. Our results demonstrate that immature kerogen is highly deformable. Within the ranges of conditions considered in this work, its density can double and its accessible porosity (to a methane molecule) can increase from 0 to \∼30\%. We also show that these deformations are significantly nonaffine (i.e., nonhomogeneous), especially upon fluid adsorption or desorption.

}, keywords = {ADSORPTION-INDUCED DEFORMATION; ORGANIC-MATTER; COMPETITIVE ADSORPTION; NANOPOROUS MEDIA; POROUS CARBONS; GLASSY-CARBON; COAL; TRANSPORT; SORPTION; MODEL}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.8b02534}, url = {http://pubs.acs.org/doi/10.1021/acs.langmuir.8b02534}, author = {Obliger, Ama{\"e}l and Valdenaire, Pierre-Louis and Capit, Nicolas and Franz-Josef Ulm and Roland Jean-Marc Pellenq and Jean-Marc Leyssale} } @article {652, title = {Synthesis, characterization, and catalytic application in aldehyde hydrosilylation of half-sandwich nickel complexes bearing (κ1-C)- and hemilabile (κ 2-C, S)-thioether-functionalised NHC ligands}, journal = {Dalton Transactions}, volume = {47}, year = {2018}, month = {Dec-21-2018}, pages = {17134-17145}, abstract = {

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

}, issn = {1477-9226}, doi = {10.1039/C8DT03882A}, url = {http://xlink.rsc.org/?DOI=C8DT03882A}, author = {Franz-Josef Ulm and Poblador-Bahamonde, Amalia I. and Choppin, Sabine and Bellemin-Laponnaz, St{\'e}phane and Chetcuti, Michael J. and Achard, Thierry and Ritleng, Vincent} } @article {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 {624, title = {Accurate classical short-range forces for the study of collision cascades in Fe{\textendash}Ni{\textendash}Cr}, journal = {Computer Physics Communications}, volume = {219}, year = {2017}, month = {Oct-2017}, pages = {11 - 19}, abstract = {

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

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

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

}, doi = {10.1051/epjconf/201714008020}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714008020}, author = {Contreras, Rafael Jaimes and Berger, Nicolas and Izard, Edouard and Douce, Jean-Fran{\c c}ois and Koltsov, Alexey and Jean-Yves Delenne and Emilien Az{\'e}ma and Saeid Nezamabadi and van Loo, Fr{\'e}d{\'e}ric and Roland Jean-Marc Pellenq and Farhang Radja{\"\i}}, editor = {Luding, S.} } @article {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 {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 {589, title = {Role of Interfaces in Elasticity and Failure of Clay{\textendash}Organic Nanocomposites: Toughening upon Interface Weakening?}, journal = {Langmuir}, volume = {33}, year = {2017}, month = {Oct-24-2017}, pages = {11457 - 11466}, abstract = {

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

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

}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.7b01071}, url = {http://pubs.acs.org/doi/10.1021/acs.langmuir.7b01071}, author = {Gy{\"o}rgy Hantal and Brochard, Laurent and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Benoit A. Coasne} } @book {636, title = {Springer Series in Geomechanics and GeoengineeringAdvances in Laboratory Testing and Modelling of Soils and Shales (ATMSS)Measurement of Mechanical Properties of Thin Clay Films and Comparison with Molecular Simulations}, series = {Springer Series in Geomechanics and Geoengineering}, year = {2017}, pages = {78-84}, publisher = {Springer International Publishing}, organization = {Springer International Publishing}, address = {Cham}, abstract = {

Here, we focus on the hydromechanical behavior of self-standing clay films with a thickness of a few dozen microns. We measure their elastic and creep properties and how those properties depend on the interlayer cation and on the relative humidity (or water content). Those experimental results are compared with the elastic and creep behavior of nanometric clay particles, which we characterize by molecular simulations. Significant qualitative differences between the behavior of the clay films and that of the clay particles are observed, which suggests that the hydromechanical behavior of the clay films is significantly impacted by their mesostructure (i.e., by how the clay particles or tactoids are arranged in space). Upscaling the hydromechanical behavior of the clay films from that of the clay particles may be challenging.

}, isbn = {978-3-319-52772-7}, issn = {1866-8755}, doi = {10.1007/978-3-319-52773-410.1007/978-3-319-52773-4_8}, url = {http://link.springer.com/10.1007/978-3-319-52773-4}, author = {Benoit Carrier and Matthieu Vandamme and Roland Jean-Marc Pellenq and Henri Van Damme}, editor = {Ferrari, Alessio and Laloui, Lyesse} } @article {596, title = {Three-dimensional bonded-cell model for grain fragmentation}, journal = {Computational Particle Mechanics}, volume = {4}, year = {2017}, month = {Oct-2017}, pages = {441 - 450}, chapter = { Special Issue: SI }, abstract = {

We present a three-dimensional numerical method for the simulation of particle crushing in 3D. This model is capable of producing irregular angular fragments upon particle fragmentation while conserving the total volume. The particle is modeled as a cluster of rigid polyhedral cells generated by a Voronoi tessellation. The cells are bonded along their faces by a cohesive Tresca law with independent tensile and shear strengths and simulated by the contact dynamics method. Using this model, we analyze the mechanical response of a single particle subjected to diametral compression for varying number of cells, their degree of disorder, and intercell tensile and shear strength. In particular, we identify the functional dependence of particle strength on the intercell strengths. We find that two different regimes can be distinguished depending on whether intercell shear strength is below or above its tensile strength. In both regimes, we observe a power-law dependence of particle strength on both intercell strengths but with different exponents. The strong effect of intercell shear strength on the particle strength reflects an interlocking effect between cells. In fact, even at low tensile strength, the particle global strength can still considerably increase with intercell shear strength. We finally show that the Weibull statistics describes well the particle strength variability.

}, keywords = {Bonded-cell model; Fragmentation; Discrete element method; Contact dynamics method; Voronoi cell; Weibull statistics}, issn = {2196-4378}, doi = {10.1007/s40571-016-0129-0}, url = {http://link.springer.com/10.1007/s40571-016-0129-0}, author = {Cantor, D and Emilien Az{\'e}ma and Philippe Sornay and Farhang Radja{\"\i}} } @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 {639, title = {Activated desorption at heterogeneous interfaces and long-time kinetics of hydrocarbon recovery from nanoporous media}, journal = {Nature Communications}, volume = {7}, year = {2016}, month = {Jun-2016}, pages = { Article Number 11890 }, abstract = {

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

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

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

}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.5b03431}, author = {Benoit Carrier and Matthieu Vandamme and Roland Jean-Marc Pellenq and Bornert, Michel and Ferrage, Eric and Hubert, Fabien and Henri Van Damme} } @article {249, title = {Free Volume Theory of Hydrocarbon Mixture Transport in Nanoporous Materials}, journal = {The Journal of Physical Chemistry Letters}, volume = {7}, year = {2016}, month = {Jun-10-2016}, pages = {3712 - 3717}, abstract = {
Despite recent focus on shale gas, hydrocarbon recovery from the ultraconfining and disordered porosity of organic matter in shales (kerogen) remains poorly understood. Key aspects such as the breakdown of hydrodynamics at the nanoscale and strong adsorption effects lead to unexplained non-Darcy behaviors. Here, molecular dynamics and statistical mechanics are used to elucidate hydrocarbon mixture transport through a realistic molecular model of kerogen [Bousige, C.; et al. Nat. Mater. 2016, 15, 576]. Owing to strong adsorption effects, velocity cross-correlations between the mixture components and between molecules of the same species are shown to be negligible. This allows estimation of each component permeance from its self-diffusivity, which can be obtained from single-component data. These permeances are found to scale with the reciprocal of the alkane length and decrease with the number of adsorbed molecules following a simple free volume theory, therefore allowing mixture transport prediction as a function of the amount of trapped fluid.
Abstract Image
}, issn = {1948-7185}, doi = {10.1021/acs.jpclett.6b01684}, author = {Ama{\"e}l Obliger and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Benoit A. Coasne} } @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 {640, title = {Nanoporous chalcogenides for adsorption and gas separation}, journal = {Physical Chemistry Chemical Physics}, volume = {18}, year = {2016}, month = {May-21-2016}, pages = {13449-13458}, abstract = {

The adsorption and gas separation properties of amorphous porous chalcogenides such as GeS2 are investigated using statistical mechanics molecular simulation. Using a realistic molecular model of such amorphous adsorbents, we show that they can be used efficiently to separate different gases relevant to environmental and energy applications (H-2, CO2, CH4, N-2). In addition to shedding light on the microscopic adsorption mechanisms, we show that coadsorption in this novel class of porous materials can be described using the ideal adsorbed solution theory (IAST). Such a simple thermodynamic model, which allows avoiding complex coadsorption measurements, describes the adsorption of mixture from pure component adsorption isotherms. Our results, which are found to be in good agreement with available experimental data, paves the way for the design of gas separation membranes using the large family of porous chalcogenides.

}, issn = {1463-9076}, doi = {10.1039/C6CP00467A}, url = {http://xlink.rsc.org/?DOI=C6CP00467A}, author = {Guido Ori and Carlo Massobrio and Pradel, Annie and Ribes, Miche and Benoit A. Coasne} } @article {641, title = {Probing Interconnectivity in Hierarchical Microporous/Mesoporous Materials Using Adsorption and Nuclear Magnetic Resonance Diffusion}, journal = {The Journal of Physical Chemistry C}, volume = {120}, year = {2016}, month = {Jan-28-2016}, pages = {1562-1569}, abstract = {

Adsorption and transport in hierarchical materials are investigated by means of adsorption and nuclear magnetic resonance experiments. Using micro/mesoporous zeolites with well-defined mesoporosity, we show that adsorption at a given pressure can be described as a simple linear combination of the adsorbed amounts taken at the same pressure for the pure microporous (zeolite FAU-Y) and mesoporous (Al-MCM-41) solids. Such a quantitative decomposition allows us to demonstrate the ability of diffusion measurements by Pulsed Field Gradient Nuclear Magnetic Resonance (PFG NMR) to probe interconnectivity in hierarchical solids. On the one hand, transport in the mechanical mixtures can be described as the superimposition of diffusion in pure microporous and mesoporous solids. On the other hand, PFG NMR for the hierarchical sample provides an effective diffusivity that is intermediate between those for the pure zeolite and mesoporous silica. Furthermore, this effective diffusivity is slower than the linear combination of the two diffusivities weighted by the number of molecules present in each phase (used in the independent domain and fast-exchange theories) clearly showing interconnectivities and transfer limitations between the microporous and mesoporous domains. We also discuss the ability of combining theories such as the fast exchange model and the effective medium theory to quantitatively predict diffusion in such microporous/mesoporous materials.

}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.5b10129}, url = {http://pubs.acs.org/doi/10.1021/acs.jpcc.5b10129}, author = {Anne Galarneau and Guenneau, Flavien and Gedeon, Antoine and Mereib, Diaa and Rodriguez, Jeremy and Fajula, Fran{\c c}ois and Benoit A. Coasne} } @article {195, title = {Realistic molecular model of kerogen{\textquoteright}s nanostructure}, journal = {Nature Materials}, year = {2016}, month = {Feb-01-2016}, abstract = {

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

Kerogen in organic-rich shale formations.

Reconstruction of molecular models of kerogens.

Experimental validation of the molecular models.

Elastic properties of molecular models of kerogen.

}, issn = {1476-1122}, doi = {10.1038/nmat4541}, author = {Bousige, Colin and Ghimbeu, Cam{\'e}lia Matei and Vix-Guterl, Cathie and Pomerantz, Andrew E. and Suleimenova, Assiya and Vaughan, Gavin and Garbarino, Gaston and Feygenson, Mikhail and Wildgruber, Christoph and Franz-Josef Ulm and Roland Jean-Marc Pellenq and Benoit A. Coasne} } @article {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} } @article {177, title = {Assessing Polarizability Models for the Simulation of Low-Frequency Raman Spectra of Benzene}, journal = {The Journal of Physical Chemistry B}, volume = {119}, year = {2015}, month = {Jul-23-2015}, pages = {9345 - 9358}, abstract = {
Abstract Image

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

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

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

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

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

}, issn = {0376-9429}, doi = {10.1007/s10704-015-0045-y}, author = {Brochard, Laurent and Gy{\"o}rgy Hantal and Hadrien Laubie and Franz-Josef Ulm and Roland Jean-Marc Pellenq and Benoit A. Coasne} } @article {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 {176, title = {Control of the Pore Texture in Nanoporous Silicon via Chemical Dissolution}, journal = {Langmuir}, volume = {31}, year = {2015}, month = {Jul-28-2015}, pages = {8121 - 8128}, abstract = {
Abstract Image

The surface and textural properties of porous silicon (pSi) control many of its physical properties essential to its performance in key applications such as optoelectronics, energy storage, luminescence, sensing, and drug delivery. Here, we combine experimental and theoretical tools to demonstrate that the surface roughness at the nanometer scale of pSi can be tuned in a controlled fashion using partial thermal oxidation followed by removal of the resulting silicon oxide layer with hydrofluoric acid (HF) solution. Such a process is shown to smooth the pSi surface by means of nitrogen adsorption, electron microscopy, and small-angle X-ray and neutron scattering. Statistical mechanics Monte Carlo simulations, which are consistent with the experimental data, support the interpretation that the pore surface is initially rough and that the oxidation/oxide removal procedure diminishes the surface roughness while increasing the pore diameter. As a specific example considered in this work, the initial roughness \ξ \∼ 3.2 nm of pSi pores having a diameter of 7.6 nm can be decreased to 1.0 nm following the simple procedure above. This study allows envisioning the design of pSi samples with optimal surface properties toward a specific process.

}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.5b01518}, author = {Secret, Emilie and Wu, Chia-Chen and Chaix, Arnaud and Anne Galarneau and Gonzalez, Philippe and Cot, Didier and Sailor, Michael J. and Jestin, Jacques and Zanotti, Jean-Marc and Cunin, Fr{\'e}d{\'e}rique and Benoit A. Coasne} } @proceedings {333, title = {Creep of Clay: Numerical Results at the Scale of a Layer and Experimental Results at the Scale of Thin Self-Standing Films}, 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 = {531-536}, publisher = {American Society of Civil Engineers}, address = {September 21{\textendash}23, 2015, Vienna, AustriaReston, VA}, abstract = {

This work focuses on the creep of clay-based materials, which exhibit significant analogies with cement-based materials. Here, we studied the creep of clay at two scales and with two techniques: numerically (with molecular simulations) at the scale of a clay layer (nm), and experimentally at the scale of thin self-standing clay films (few dozen m). At the scale of the clay layer, numerical simulations showed that the shear rate was constant over time and an affine function of the shear stress. Creep experiments showed that, after a transient period, the creep function of our thin self-standing clay films was a logarithmic function of time. A comparison of the results obtained at the two scales shows that the origin of the logarithmic feature of clay creep must at least partly originate from a scale greater than that of an individual clay layer. By analogy, such result is likely to hold for cementitious materials, which are also known to creep logarithmically with respect to time in the long term: the origin of this logarithmic feature is likely to stem at least partly from a scale greater than the scale of an individual C-S-H layer.

}, doi = {10.1061/978078447934610.1061/9780784479346.064}, author = {Benoit Carrier and Matthieu Vandamme and Roland Jean-Marc Pellenq and Henri Van Damme}, editor = {Hellmich, Christian and Pichler, Bernhard and Kollegger, Johann} } @article {135, title = {Effect of Chain Length and Pore Accessibility on Alkane Adsorption in Kerogen}, journal = {Energy \& Fuels}, volume = {29}, year = {2015}, month = {Oct-28-2015}, pages = {7889 - 7896}, abstract = {
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Configurational-biased Grand Canonical Monte Carlo and Molecular Dynamics simulations were used to investigate the adsorption and structure of n-alkanes in realistic models of kerogen (the organic phase in gas shales). Both the effects of the n-alkane length (from methane to dodecane) and of the adsorbent porosity/density and connectivity were considered. For all n-alkanes, due to the subnano pore size of kerogen, adsorption follows a Langmuir-type adsorption isotherm as the adsorbed amount increases continuously with pressure until maximum loading is reached. While all n-alkanes get adsorbed very efficiently in low density kerogen, size exclusion in high density kerogen lead to low adsorbed amounts for molecules larger than hexane. Using Molecular Dynamics simulations reflecting the setup of actual adsorption experiments, we also probed the effect of pore accessibility on n-alkane adsorption in kerogen. All pores are connected to the surface and, hence, accessible for the low density kerogen. In contrast, most pores are isolated and inaccessible in the kerogen with the high density. We also address the effect of mesoporosity and its connection to nanoporosity on alkane adsorption in kerogen.

}, issn = {0887-0624}, doi = {10.1021/acs.energyfuels.5b02015}, author = {Kerstyn I. Falk and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Benoit A. Coasne} } @article {182, title = {Effect of Surface Texture on Freezing in Nanopores: Surface-Induced versus Homogeneous Crystallization}, journal = {Langmuir}, volume = {31}, year = {2015}, month = {Mar-10-2015}, pages = {2706 - 2713}, abstract = {
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Freezing of argon in ordered and disordered carbon pores of a similar diameter D \∼ 2.4 nm is investigated using extensive molecular simulations with large system sizes up to 104 atoms. While crystallization in the atomistically smooth pore consists in a surface-induced phase transition occurring at a temperature larger than the bulk, crystallization in the disordered pores, which is only partial as it is spatially restricted to the pore center, occurs through homogeneous crystallization. These results shed light on solidification in pores by showing that there is a crossover between surface-induced and homogeneous crystallization upon increasing the surface disorder of the host material. In the latter case, the Gibbs\–Thomson equation, in which crystallization is assumed to occur when the crystal size equals the pore size corrected for the thickness of the unfreezable layer at the pore surface, is in reasonable agreement with the observed freezing temperature.

}, issn = {0743-7463}, doi = {10.1021/la5041213}, author = {Benoit A. Coasne} } @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} } @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 {183, title = {Mechanism of H2O Insertion and Chemical Bond Formation in AlPO 4-54{\textperiodcentered}x H2O at High Pressure}, journal = {Journal of the American Chemical Society}, volume = {137}, year = {2015}, month = {Jan-21-2015}, pages = {584 - 587}, abstract = {

The insertion of H2O in AlPO4-54\•xH2O at high pressure was investigated by single-crystal x-ray diffraction and Monte Carlo molecular simulation. H2O molecules are concentrated, in particular near the pore walls. Upon insertion, the additional water is highly disordered. Insertion of H2O (superhydration) is found to impede pore collapse in the material, thereby strongly modifying its mechanical behavior. However, instead of stabilizing the structure with respect to amorphization, the results provide evidence for the early stages of chemical bond formation between H2O molecules and tetrahedrally coordinated aluminum, which is at the origin of the amorphization/reaction process.

}, issn = {0002-7863}, doi = {10.1021/ja511153n}, author = {Alabarse, Frederico G. and Rouquette, J{\'e}r{\^o}me and Benoit A. Coasne and Haidoux, Abel and Paulmann, Carsten and Cambon, Olivier and Haines, Julien} } @proceedings {358, title = {Micromechanical analysis of the surface erosion of a cohesive soil by means of a coupled LBM-DEM model}, journal = {IV International Conference on Particle-based Methods (PARTICLES 2015)}, volume = {PARTICLE-BASED METHODS IV-FUNDAMENTALS AND APPLICATIONS}, year = {2015}, month = {sept-30-2015}, pages = {519-528}, publisher = {International Center for Numerical Methods in Engineering (CIMNE)}, address = {SEP 28-30 2015 Barcelona, SPAIN}, abstract = {

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

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

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

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

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

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}, issn = {0021-9606}, doi = {10.1063/1.4914921}, author = {Bousige, Colin and Botan, Alexandru and Franz-Josef Ulm and Roland Jean-Marc Pellenq and Benoit A. Coasne} } @article {141, title = {Organic{\textendash}Clay Interfacial Chemical Bonds Probed by ab Initio Calculations}, journal = {The Journal of Physical Chemistry C}, volume = {119}, year = {2015}, month = {Mar-26-2015}, pages = {6511 - 6517}, abstract = {
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Evaluating the nature of binding of the organic phase (called kerogen) with clays and other minerals in gas and oil shale is of critical importance for developing optimal processes for hydrocarbon extraction and recovery. Here we report the results of an ab initio reactive study of a gaseous oil/clay interface, which consists of grafting fragments of sp3 methane and sp2 benzene onto the basal surface of illite. Methane and benzene fragments were selected as they correspond to the simplest monomers of the immature (aliphatic sp3 carbon atoms) and mature (aromatic sp2 carbon atoms) stages of the kerogen macromolecule while illite is encountered in many shale formations. We find that the methyl or phenyl radicals always bond upright to one of the outmost Si atoms of the clay phase, while the H atom attaches to the inner Al\–OH group forming a water molecule. The covalent attachment of the radicals to the oxygen atoms of the clay surface is always less favorable than to the silicon atoms. The energetics of these grafted adducts are discussed along with the maturation state of the shale. An unanticipated signature of the covalent Si\–C binding is the formation of hypervalent Si complexes, characterized by elongated bonds at the oil/clay interface. We complement our atomistic modeling by simulating IR spectra of the two covalently grafted interfaces (methyl\–illite and phenyl\–illite) which fingerprint elongated Si\–C bonds in the frequency range 1100\–1250 cm\–1. This novel finding should have a large impact on the understanding of fracking conditions in shales through this tight- and loose-bonded organic/inorganic interface.

}, issn = {1932-7447}, doi = {10.1021/jp510885f}, author = {Bocquet, Marie-Laure and Benoit A. Coasne and Roland Jean-Marc Pellenq and Franz-Josef Ulm} } @article {178, title = {Polarized Water Wires under Confinement in Chiral Channels}, journal = {The Journal of Physical Chemistry B}, volume = {119}, year = {2015}, month = {Jul-16-2015}, pages = {8707 - 8717}, abstract = {
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The alignment of water molecules along chiral pores may activate proton/ion conduction along dipolar hydrophilic pathways. Here we show that a simple synthetic \“T-channel\” forms a directional pore with its carbonyl moieties solvated by chiral helical water wires. Atom-scale simulations and experimental crystallographic assays reveal a dynamical structure of water and electrolyte solutions (alkali metal chlorides) confined in these organic T-channels. Oscillations in the dipole orientation, which correspond to alternative ordering (dipole up\–dipole down) of the water molecules with a period of about 4.2 \Å (imposed by the distance between two successive carbonyl groups) are observed. When ions are added to the system, despite the strong Coulombic water/ion interaction, confined water remains significantly ordered in the T-channel and still exhibits surface-induced polarization. Cation permeation can be achieved through alternated hydration\–dehydration occurring along strongly oriented water wires. The T-channel, which exhibits chirality with strong water orientation, provides an opportunity to unravel novel water-channel systems that share many interesting properties of biomolecular systems.

}, issn = {1520-6106}, doi = {10.1021/acs.jpcb.5b03322}, author = {Barboiu, Mihail and Pierre-Andre Cazade and Le Duc, Yann and Yves-Marie Legrand and Arie Van Der Lee and Benoit A. Coasne} } @article {181, title = {Predicting Adsorption on Bare and Modified Silica Surfaces}, journal = {The Journal of Physical Chemistry C}, volume = {119}, year = {2015}, month = {Mar-19-2015}, pages = {6009 - 6017}, abstract = {
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We show that Derjaguin\’s theory of adsorption can be used to predict adsorption on bare and modified surfaces using parameters available to simple experiments. Using experiment and molecular simulation of adsorption of various gases on hydroxylated, methylated, and trifluoromethylated silica, this simple parametrization of Derjaguin\’s model allows predicting adsorption on any functionalized surface using a minimum set of parameters such as the heat of vaporization of the adsorbate and the Henry constant of the adsorption isotherm. This general yet simple scheme constitutes a powerful tool as it avoids having to carry out tedious and complex adsorption measurements.

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

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

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}, issn = {13871811}, doi = {10.1016/j.micromeso.2015.05.050}, author = {L{\'e}pinay, Matthieu and Broussous, Lucile and Licitra, Christophe and Bertin, Fran{\c c}ois and Rouessac, Vincent and Ayral, Andre and Benoit A. Coasne} } @article {175, title = {Solubility of Gases in Water Confined in Nanoporous Materials: ZSM-5, MCM-41, and MIL-100}, journal = {The Journal of Physical Chemistry C}, volume = {119}, year = {2015}, month = {Sep-17-2015}, pages = {21547 - 21554}, abstract = {
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Oversolubility, which corresponds to large apparent gas solubilities in liquids confined in nanoporous solids, has been proposed as a means to develop novel adsorption, phase separation, or catalytic processes. We report a molecular simulation study to help design such hybrid adsorbents consisting of a solvent confined in host nanoporous materials. Water is selected as the confined solvent because of its ubiquity in industrial applications, while N2, CH4, and CO2 are selected as they allow probing the effect of specific molecular interaction and polarity. For each system, we consider a zeolite, an ordered mesoporous silica, and a metal\–organic framework as the confining host as they present different morphologies, porosities, and surface chemistries. We show that oversolubility is always observed because the apparent solubility in these materials surpasses the bulk solubility. In all cases, oversolubility is an enhanced bulklike solubility in which solubility is favored in the regions of low water density formed by the layering of the solvent. Such an oversolubility mechanism, which arises from the fact that the gas\–solid interactions are weaker than the solvent\–solid interactions, leads to large uptakes as high as a few hundred times that expected from bulk solubility.

}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.5b06660}, author = {Linh Ngoc Ho and Schuurman, Yves and David Farrusseng and Benoit A. Coasne} } @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 {180, title = {Structure and Dynamics of Ionic Liquids Confined in Amorphous Porous Chalcogenides}, journal = {Langmuir}, volume = {31}, year = {2015}, month = {Jun-23-2015}, pages = {6742 - 6751}, abstract = {
Abstract Image

Besides the abundant literature on ionic liquids in porous silica and carbon, the confinement of such intriguing liquids in porous chalcogenides has received very little attention. Here, molecular simulation is employed to study the structural and dynamical properties of a typical ionic liquid confined in a realistic molecular model of amorphous chalcogenide with various pore sizes and surface chemistries. Using molecular dynamics in the isobaric\–isothermal (NPT) ensemble, we consider confinement conditions relevant to real samples. Both the structure and self-dynamics of the confined phase are found to depend on the surface-to-volume ratio of the host confining material. Consequently, most properties of the confined ionic liquid can be written as a linear combination of surface and bulk-like contributions, arising from the ions in contact with the surface and the ions in the pore center, respectively. On the other hand, collective dynamical properties such as the ionic conductivity remain close to their bulk counterpart and almost insensitive to pore size and surface chemistry. These results, which are in fair agreement with available experimental data, provide a basis for the development of novel applications using hybrid organic\–inorganic solids consisting of ionic liquids confined in porous chalcogenides.

}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.5b00982}, author = {Guido Ori and Carlo Massobrio and Pradel, Annie and Ribes, Michel and Benoit A. Coasne} } @article {132, title = {Subcontinuum mass transport of condensed hydrocarbons in nanoporous media.}, journal = {Nat Commun}, volume = {6}, year = {2015}, month = {Apr-22-2015}, pages = {Article Number: 6949}, abstract = {

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

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

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

}, keywords = {DEM, Fluidization, Granular Materials, LBM}, url = {https://hal.archives-ouvertes.fr/hal-01269325}, author = {Jeff Ngoma and Pierre Philippe and St{\'e}phane Bonelli and Cuellar, Pablo and Jean-Yves Delenne and Farhang Radja{\"\i}}, editor = {Onate, E and Bischoff, M and Owen, DRJ} } @article {108, title = {Adsorption and Dynamics in Hierarchical Metal-Organic Frameworks}, journal = {Journal of Physical Chemistry C}, volume = {118}, year = {2014}, month = {Apr-10-2014}, pages = {7423-7433}, type = {Article}, abstract = {

Adsorption and dynamics in hierarchical metal-organic frameworks are investigated by means of molecular simulation. The models of hierarchical porous solids are obtained by carving mesopores of different diameters out of a crystal of Cu-BTC (model A) or by inserting a microporous particle of Cu-BTC in an amorphous silica mesopore (model B). We show that the nitrogen adsorption isotherms at 77 K for the solids corresponding to model A can be described as a linear combination of reference adsorption isotherms for pure microporous and mesoporous solids. In contrast, the adsorption isotherms for model B cannot be described accurately as a sum of reference microporous and mesoporous adsorption isotherms. The inserted particle acts as a constriction which helps nucleate the liquid phase within the mesopore so that no capillary condensation hysteresis is observed. The dynamics of nitrogen adsorbed at 77 K inside the porosity of the hierarchical solids is also investigated. The Fickian regime is reached at long times which are not attainable with molecular dynamics simulations. At higher temperature, the faster self-diffusion makes it possible to obtain the diffusivity of the adsorbate. Nitrogen adsorbed in the microporosity of the hierarchical porous solids has a self-diffusion coefficient close to that of nitrogen adsorbed in pure Cu-BTC. In contrast, diffusion in the mesoporosity is faster than in the microporosity so that the overall diffusivity is faster than in pure Cu-BTC.

\<\>Abstract Image

}, issn = {1932-7447}, doi = {10.1021/jp500037z}, author = {Fran{\c c}ois Villemot and Anne Galarneau and Benoit A. Coasne} } @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 {64, title = {Adsorption-based characterization of hierarchical metal{\textendash}organic frameworks}, journal = {Adsorption}, volume = {20}, year = {2014}, month = {Feb-2014}, pages = {349-357}, abstract = {

Nitrogen adsorption at 77 K on metal\–organic framework (MOF) is investigated by means of molecular simulations. We consider both regular Cu\–BTC crystal and a MOF-based hierarchical porous solid consisting of a mesopore carved out of a Cu\–BTC crystal. The t-plot method is applied to these solids by using a non-porous Cu\–BTC surface as the reference sample. The values of the mesoporous and external surface areas are determined from the t-plot, and the validity of the method for this type of hierarchical solid is discussed.

}, keywords = {Adsorption, Hierarchical porous materials, Molecular simulation, t-Plot}, issn = {0929-5607}, doi = {10.1007/s10450-013-9583-7}, author = {Fran{\c c}ois Villemot and Anne Galarneau and Benoit A. Coasne} } @article {107, title = {An artificial primitive mimic of the Gramicidin-A channel}, journal = {Nature Communications}, volume = {5}, year = {2014}, month = {Jun-26-2014}, type = {Article}, abstract = {

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

Molecular structures and crystal packing.

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

Bilayer membrane transport experiments.

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

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

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

}, keywords = {clay, elastic properties, fracture, reactive molecular simulation}, issn = {0026-8976}, doi = {10.1080/00268976.2014.897393}, author = {Gy{\"o}rgy Hantal and Brochard, Laurent and Hadrien Laubie and Ebrahimi, Davoud and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Benoit A. Coasne} } @article {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} } @article {101, title = {Effect of temperature on adsorption of mixtures in porous materials}, journal = {Molecular Simulation}, volume = {40}, year = {2014}, month = {Jan-02-2014}, pages = {45-51}, type = {Article}, abstract = {

The effect of temperature on the adsorption of a simple mixture (Ar/Kr) in disordered porous materials is investigated by means of molecular simulation. In the larger mesopores of porous silica glasses, capillary condensation occurs upon decreasing the temperature. At temperatures above the capillary condensation temperature, Kr is preferentially adsorbed at the pore surface and Ar adsorption occurs in regions of low Kr density. For temperatures below the capillary condensation temperature, Ar density surprisingly increases as temperature increases, the behaviour that is consistent with an over-solubility effect. In contrast, in the disordered sub-nanoporous carbon, filling of the pores occurs in a reversible and continuous way upon decreasing the temperature, owing to the small size and amorphous shape of the pores. These results show that the crossover between capillary condensation and continuous reversible filling observed for pure fluids in pores also exists for mixtures. We also show that the Kr selectivity exhibits a minimum in the disordered porous silica that is located at the capillary condensation temperature. In contrast, in the disordered porous carbon where no capillary condensation occurs, the selectivity decreases monotonically with increasing the temperature. These results shed light on low-temperature adsorption of mixtures confined in porous materials and provide a guide to design efficient phase separation processes.

}, keywords = {Adsorption, grand canonical Monte Carlo simulations, Mixtures, porous materials}, issn = {0892-7022}, doi = {10.1080/08927022.2013.852192}, author = {Kerstyn I. Falk and Benoit A. Coasne and Roland Jean-Marc Pellenq} } @article {114, title = {Elastic Properties of Swelling Clay Particles at Finite Temperature upon Hydration}, journal = {Journal of Physical Chemistry C}, volume = {118}, year = {2014}, month = {May-01-2014}, pages = {8933-8943}, type = {Article}, abstract = {
Abstract Image

The knowledge of mechanical properties of swelling clays on the scale of the clay layer is of crucial importance to build predictive hydromechanical macroscopic constitutive laws in a bottom-up approach. In this work, we computed the elastic properties of particles of a swelling clay (i.e., montmorillonite) by molecular dynamics simulations. Because of the softness of the material in the direction orthogonal to the clay layer with increasing water content, the computation of the whole stiffness tensor was not trivial: we needed to implement the elastic bath method,1 which allows us to attenuate thermal strains and compute the stiffness via strain fluctuations in isothermal\–isobaric simulations. We investigated the effect of water content, temperature, and the interlayer cation on the elastic properties of swelling clays. In particular, we showed that the out-of-plane stiffness coefficients computed at 300 K differed significantly from the same coefficients computed at 0 K. The out-of-plane coefficients were very sensitive to both temperature and water content. In contrast, the dependence of the in-plane coefficients to temperature was slight. Moreover, the decrease of the in-plane coefficients with water content could be entirely explained by the change of geometry of the system due to the swelling of the interlayer space. The interlayer cation impacted the elastic properties of montmorillonite only in the driest states.

}, issn = {1932-7447}, doi = {10.1021/jp412160e}, author = {Benoit Carrier and Matthieu Vandamme and Roland Jean-Marc Pellenq and Henri Van Damme} } @article {85, title = {Enhanced H-2 Uptake of n-Alkanes Confined in Mesoporous Materials}, journal = {Journal of Physical Chemistry C }, volume = {118}, year = {2014}, month = {Apr-30-2014}, pages = {10720-10727}, type = {Article}, abstract = {
Abstract Image

The hydrogen uptake in hybrid sorbents consisting of n-alkane solvents confined in mesoporous silica aerogel is measured at different temperatures from 273 to 313 K and pressures up to 40 bar. An apparent \“oversolubility\” effect is observed as the H2 uptake in the hybrid sorbents is much larger than that in bulk solvents. The H2 uptake in the hybrid sorbents is found to increase with increasing temperature, which suggests that the flexibility and conformation of n-alkane molecules confined in the aerogel play a crucial role; high-entropy (disordered) alkane configurations lead to the creation of numerous cavities which make it possible to solubilize a larger number of H2 molecules. This departs from adsorption-driven solubility effects for which the number of solubilized molecules decreases with increasing temperature. For a given temperature and pressure, it is found that the number of solubilized H2 molecules per unit volume increases with decreasing alkane chain length. Such an effect, which is observed for both the bulk alkanes and the alkanes confined in the silica aerogel, can be rationalized by considering the number density of CHx (x = 2 or 3) groups; for a given temperature, the latter number density decreases with decreasing alkane chain length so that the free volume available to solubilize H2 molecules increases.

}, issn = {1932-7447}, doi = {10.1021/jp411526f}, author = {St{\'e}phanie Clauzier and Linh Ngoc Ho and Pera-Titus, M. and David Farrusseng and Benoit A. Coasne} } @article {83, title = {Ionic liquid confined in silica nanopores: molecular dynamics in the isobaric-isothermal ensemble}, journal = {Molecular Physics}, volume = {112}, year = {2014}, month = {Avr-03-2014}, pages = {1350-1361}, type = {Article}, abstract = {

Molecular dynamics simulations in the isobaric-isothermal ensemble are used to investigate the structure and dynamics of an ionic liquid confined at ambient temperature and pressure in hydroxylated amorphous silica nanopores. The use of the isobaric-isothermal ensemble allows estimating the effect of confinement and surface chemistry on the density of the confined ionic liquid. The structure of the confined ionic liquid is investigated using density profiles and structural order parameters while its dynamics is assessed by determining the mobility and ionic conductivity of the confined phase. Despite the important screening of the electrostatic interactions (owing to the small Debye length in ionic liquids), the local structure of the confined ionic liquid is found to be mostly driven by electrostatic interactions. We show that both the structure and dynamics of the confined ionic liquid can be described as the sum of a surface contribution arising from the ions in contact with the surface and a bulk-like contribution arising from the ions located in the pore centre; as a result, most properties of the confined ionic liquid are a simple function of the surface-to-volume ratio of the host porous material. In contrast, the ionic conductivity of the confined ionic liquid, which is a collective dynamical property, is found to be similar to the bulk. This study sheds light on the complex behaviour of hybrid materials made up of ionic liquid confined in inorganic porous materials.

}, keywords = {amorphous silica, ionic liquids, molecular dynamics, surface}, issn = {0026-8976}, doi = {10.1080/00268976.2014.902138}, author = {Guido Ori and Fran{\c c}ois Villemot and Lydie Viau and Andre Vioux and Benoit A. Coasne} } @article {69, title = {Molecular dynamics simulations of the formation of 1D spin-valves from stretched Au-Co and Pt-Co nanowires}, journal = {J. Phys.: Condens. Matter}, volume = {26}, year = {2014}, month = {Oct-2014}, chapter = {474206}, abstract = {

We have performed molecular dynamics (MD) simulations of stretched Aux-Co1 - x and Ptx-Co1 - x nanowires to investigate the formation of bimetallic monoatomic wires between two electrodes. We have considered nanowires with two concentrations x = 0.2 and 0.8, aspect ratio of 13, a cross section of 1 nm(2) and a wide range of temperatures (from 10 to 400 K). For the MD simulations we have used a semi-empirical interatomic potential based on the second moment approximation (SMA) of the density of states to the tight-binding Hamiltonian.For Au-Co alloys, Au atoms tends to migrate towards the narrowed region to form almost pure Au wires. In the PtCo case the formed chains usually consist of Pt enriched alternating structures. The most striking result is probably the Au(0.2)-Co(0.8) alloy where pure monoatomic Au chains form between two Co electrodes constituting a potential 1D spin valve. Despite the known ease with which the 5d metals (Pt, Ir, and Au) form monoatomic chains (MACS), our results show that in the presence of Co (x = 0.2), the percentage of chain formation is higher than in the Pt and Au rich cases (x = 0.8).

}, doi = {10.1088/0953-8984/26/47/474206}, author = {Robinson Cortes-Huerto and T. Sondon and Andres Sa{\`u}l} } @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.

Figure

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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 {649, title = {Poroelastic Theory Applied to the Adsorption-Induced Deformation of Vitreous Silica}, journal = {The Journal of Physical Chemistry B}, volume = {118}, year = {2014}, month = {Dec-11-2014}, pages = {14519 - 14525}, abstract = {

When vitreous silica is submitted to high pressures under a helium atmosphere, the change in volume observed is much smaller than expected from its elastic properties. It results from helium penetration into the interstitial free volume of the glass network. We present here the results of concurrent spectroscopic experiments using either helium or neon and molecular simulations relating the amount of gas adsorbed to the strain of the network. We show that a generalized poromechanical approach, describing the elastic properties of microporous materials upon adsorption, can be applied successfully to silica glass in which the free volume exists only at the subnanometer scale. In that picture, the adsorption-induced deformation accounts for the small apparent compressibility of silica observed in experiments.

}, issn = {1520-6106}, doi = {10.1021/jp5094383}, url = {http://pubs.acs.org/doi/10.1021/jp5094383}, author = {Benoit A. Coasne and Weigel, Coralie and Polian, Alain and Kint, Mathieu and Rouquette, J{\'e}r{\^o}me and Haines, Julien and Foret, Marie and Vacher, Rene and Ruffle, Benoit} } @article {87, title = {Pressure effects in confined nanophases}, journal = {Molecular Simulation}, volume = {40}, year = {2014}, month = {Feb-05-2014}, pages = {721-730}, type = {Article}, abstract = {

In this article, we review how pressure effects in pores affect both the physics of the confined fluid and the properties of the host porous material. Molecular simulations in which high-pressure effects were observed are first discussed; we will see how the strong dependence on bulk phase pressure of the freezing temperature of a fluid confined in nanopores can be explained by important variations of the pressure within the pore. We then discuss recent works in which direct calculations of the pressure tensor of fluids confined in pores provide evidence for large pressure enhancements. Finally, practical applications of these pressure effects in which gas adsorption in microporous solids (pore size \<2nm) was found to enhance their mechanical properties by increasing the elastic modulus by a factor 4 are discussed.

}, keywords = {confinement, high-pressure effects, mechanical properties, porous materials}, issn = {0892-7022}, doi = {10.1080/08927022.2013.829227}, author = {Benoit A. Coasne and Yun Long and Keith E. Gubbins} } @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} } @article {63, title = {Structure and Dynamics of an Electrolyte Confined in Charged Nanopores}, journal = {The Journal of Physical Chemistry C}, volume = {118}, year = {2014}, month = {Feb-2014}, pages = {5061{\textendash}5072}, abstract = {
Abstract Image

Molecular Dynamics simulations are used to investigate the structure and dynamics of an aqueous electrolyte (NaCl) confined within a nanomembrane, which consists of a nanopore with a diameter 3 nm having a negatively charged surface. Both nanomembranes with a diffuse charge and with local charges are considered (in both cases, two surface charge densities are considered, \−0.9 e/nm2 and \−1.8 e/nm2). For all nanomembranes, significant layering of water and ions in the vicinity of the nanomembrane surface is observed. While the distribution of water and chloride ions is nearly insensitive to the nanomembrane charge and type, the arrangement of sodium cations within the nanomembrane depends on the system being considered. The water and ion density profiles in the nanomembranes are compared with the predictions of a modified Poisson\–Boltzmann equation in which charge image, solvation effects, and dispersion interactions with the surface are taken into account [Huang et al. Langmuir, 2008, 24, 1442]. The self-diffusion coefficient for a given species is smaller than its bulk counterpart and is at most 75\% of the bulk value. While the self-diffusion coefficients for water and sodium cations decrease with decreasing the overall negative charge of the nanomembrane, the self-diffusion coefficient for the chloride anions is nearly independent of the nanomembrane type and charge. We also estimate the dynamics of the confined aqueous electrolyte by calculating time correlation functions which allow estimating solvation, ion pairing, and residence times.

}, isbn = {1932-7447}, doi = {10.1021/jp4098638}, author = {Pierre-Andre Cazade and Hartkamp, Remco and Benoit A. Coasne} } @article {90, title = {Structure and transport of aqueous electrolytes: From simple halides to radionuclide ions}, journal = {Journal of Chemical Physics}, volume = {141}, year = {2014}, month = {Sept-28-2014}, pages = {124508}, type = {Article}, abstract = {

Molecular simulations are used to compare the structure and dynamics of conventional and radioactive aqueous electrolytes: chloride solutions with sodium, potassium, cesium, calcium, and strontium. The study of Cs+ and Sr2+ is important because these radioactive ions can be extremely harmful and are often confused by living organisms for K+ and Ca2+, respectively. Na+, Ca2+, and Sr2+ are strongly bonded to their hydration shell because of their large charge density. We find that the water molecules in the first hydration shell around Na+ form hydrogen bonds between each other, whereas molecules in the first hydration shell around Ca2+ and Sr2+ predominantly form hydrogen bonds with water molecules in the second shell. In contrast to these three ions, K+ and Cs+ have low charge densities so that they are weakly bonded to their hydration shell. Overall, the structural differences between Ca2+ and Sr2+ are small, but the difference between their coordination numbers relative to their surface areas could potentially be used to separate these ions. Moreover, the different decays of the velocity-autocorrelation functions corresponding to these ions indicates that the difference in mass could be used to separate these cations. In this work, we also propose a new definition of the pairing time that is easy to calculate and of physical significance regardless of the problem at hand. (C) 2014 AIP Publishing LLC.

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}, issn = {0021-9606}, doi = {10.1063/1.4896380}, author = {Hartkamp, Remco and Benoit A. Coasne} } @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 {32, title = {Surface Chemistry and Atomic-Scale Reconstruction of Kerogen-Silica Composites}, journal = {The Journal of Physical Chemistry C}, volume = {118}, year = {2014}, month = {Feb-6-2014}, pages = {2429-2438}, abstract = {
Abstract Image

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

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

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

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

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

}, issn = {0743-7463}, doi = {10.1021/la404166y}, author = {Tourne-Peteilh, Corine and Benoit A. Coasne and In, Martin and Brevet, David and Devoisselle, Jean-Marie and Andre Vioux and Lydie Viau} } @article {92, title = {Validity of the t-plot Method to Assess Microporosity in Hierarchical Micro/Mesoporous Materials}, journal = {Langmuir}, volume = {30}, year = {2014}, month = {Nov-2014}, pages = {13266-13274}, type = {Article}, abstract = {
Abstract Image

The t-plot method is a well-known technique which allows determining the micro- and/or mesoporous volumes and the specific surface area of a sample by comparison with a reference adsorption isotherm of a nonporous material having the same surface chemistry. In this paper, the validity of the t-plot method is discussed in the case of hierarchical porous materials exhibiting both micro- and mesoporosities. Different hierarchical zeolites with MCM-41 type ordered mesoporosity are prepared using pseudomorphic transformation. For comparison, we also consider simple mechanical mixtures of microporous and mesoporous materials. We first show an intrinsic failure of the t-plot method; this method does not describe the fact that, for a given surface chemistry and pressure, the thickness of the film adsorbed in micropores or small mesopores (\< 10\σ, \σ being the diameter of the adsorbate) increases with decreasing the pore size (curvature effect). We further show that such an effect, which arises from the fact that the surface area and, hence, the free energy of the curved gas/liquid interface decreases with increasing the film thickness, is captured using the simple thermodynamical model by Derjaguin. The effect of such a drawback on the ability of the t-plot method to estimate the micro- and mesoporous volumes of hierarchical samples is then discussed, and an abacus is given to correct the underestimated microporous volume by the t-plot method.

}, issn = {0743-7463}, doi = {10.1021/la5026679}, author = {Anne Galarneau and Fran{\c c}ois Villemot and Rodriguez, Jeremy and Fajula, Fran{\c c}ois and Benoit A. Coasne} } @article {88, title = {Water adsorption in MOFs: fundamentals and applications}, journal = {Chemical Society Reviews}, volume = {43}, year = {2014}, month = {Aug-2014}, pages = {5594-5617}, type = {Review}, abstract = {

This review article presents the fundamental and practical aspects of water adsorption in Metal\–Organic Frameworks (MOFs). The state of the art of MOF stability in water, a crucial issue to many applications in which MOFs are promising candidates, is discussed here. Stability in both gaseous (such as humid gases) and aqueous media is considered. By considering a non-exhaustive yet representative set of MOFs, the different mechanisms of water adsorption in this class of materials are presented: reversible and continuous pore filling, irreversible and discontinuous pore filling through capillary condensation, and irreversibility arising from the flexibility and possible structural modifications of the host material. Water adsorption properties of more than 60 MOF samples are reported. The applications of MOFs as materials for heat-pumps and adsorbent-based chillers and proton conductors are also reviewed. Some directions for future work are suggested as concluding remarks.

Graphical abstract: Water adsorption in MOFs: fundamentals and applications
}, issn = {0306-0012}, doi = {10.1039/c4cs00078a}, author = {Canivet, Jerome and Fateeva, Alexandra and Guo, Youmin and Benoit A. Coasne and David Farrusseng} } @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} } @article {81, title = {Adsorption-based characterization of hierarchical metal-organic frameworks}, journal = {Adsorptio-Journal of the International Adsorption Society}, volume = {20}, year = {2013}, month = {Oct-06-2013}, pages = {349-357}, type = {Article}, abstract = {

Nitrogen adsorption at 77 K on metal-organic framework (MOF) is investigated by means of molecular simulations. We consider both regular Cu-BTC crystal and a MOF-based hierarchical porous solid consisting of a mesopore carved out of a Cu-BTC crystal. The t-plot method is applied to these solids by using a non-porous Cu-BTC surface as the reference sample. The values of the mesoporous and external surface areas are determined from the t-plot, and the validity of the method for this type of hierarchical solid is discussed.

}, keywords = {Adsorption, Hierarchical porous materials, Molecular simulation, t-Plot}, issn = {0929-5607}, doi = {10.1007/s10450-013-9583-7}, author = {Fran{\c c}ois Villemot and Anne Galarneau and Benoit A. Coasne} } @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} } @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 {46, title = {ESEM Study of the Humidity-Induced Swelling of Clay Film}, journal = {Langmuir}, volume = {29}, year = {2013}, month = {Oct-02-2013}, pages = {12823{\textendash}12833}, abstract = {
Abstract Image

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

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

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

}, issn = {1098-0121}, doi = {10.1103/PhysRevB.88.174201}, author = {Celino, M. and Le Roux, S. and Guido Ori and Benoit A. Coasne and Bouzid, A. and Boero, M. and Carlo Massobrio} } @article {33, title = {Gas uptake in solvents confined in mesopores: adsorption versus enhanced solubility}, journal = {The Journal of Physical Chemistry Letters}, volume = {4}, year = {2013}, month = {Jun-25-2013}, pages = {2274{\textendash}2278}, abstract = {
Abstract Image

Three molecular mechanisms for gas uptake in a solvent confined in mesopores are identified. On the one hand, CO2 uptake is an adsorption-driven phenomenon that arises from the strong interaction between the gas molecules and the pore surface. On the other hand, H2 uptake is a confinement-induced enhanced solubility in which solubility is favored in the regions of low solvent density formed by the layering of the solvent. In partially filled pores, adsorption at the gas/liquid solvent interface is a third mechanism that leads to large gas uptakes. This study, which sheds light on previously reported yet unclear oversolubility in pores, provides a guide to design hybrid porous catalysts consisting of a solvent confined in a porous solid.

}, doi = {10.1021/jz401143x}, author = {Linh Ngoc Ho and St{\'e}phanie Clauzier and Schuurman, Yves and David Farrusseng and Benoit A. Coasne} } @proceedings {370, title = {GRANULAR SLUMPING IN A FLUID : FOCUS ON RUNOUT DISTANCES}, journal = {3rd International Conference on Particle-based Methods}, volume = {PARTICLE-BASED METHODS III: FUNDAMENTALS AND APPLICATIONS}, year = {2013}, month = {Sept-2013}, pages = {115-123}, address = {SEP 18-20 2013 Stuttgart, GERMANY}, author = {Vincent Topin and Yann Monerie and Perales, F.}, editor = {Bischoff, M and Ramm, E and Onate, E} } @article {25, title = {Large pressure enhancements in confined phases: effect of surface chemistry and roughness}, journal = {J. Chem. Phys.}, volume = {139}, year = {2013}, month = {Oct-10-2013}, chapter = {144701}, abstract = {

Experiments and simulations both suggest that the pressure experienced by an adsorbed phase confined within a carbon nanoporous material can be several orders of magnitude larger than the bulk phase pressure in equilibrium with the system. To investigate this pressure enhancement, we report a molecular-simulation study of the pressure tensor of argon confined in slit-shaped nanopores with walls of various models, including carbon and silica materials. We show that the pressure is strongly enhanced by confinement, arising from the effect of strongly attractive wall forces; confinement within purely repulsive walls does not lead to such enhanced pressures. Simulations with both the Lennard-Jones and Barker-Fisher-Watts intermolecular potentials for argon-argon interactions give rise to similar results. We also show that an increase in the wall roughness significantly decreases the in-pore pressure due to its influence on the structure of the adsorbate. Finally, we demonstrate that the pressures calculated from the mechanical (direct pressure tensor calculations) and the thermodynamic (volume perturbation method) routes yield almost identical results, suggesting that both methods can be used to calculate the local pressure tensor components in the case of these planar geometries.

Image of FIG. 1.
Image of FIG. 2.
Image of FIG. 3.
Image of FIG. 4.
}, doi = {10.1063/1.4824125}, author = {Yun Long and Jeremy C. Palmer and Benoit A. Coasne and Malgorzata Sliwinska-Bartkowiak and George Jackson and Erich A. Mueller and Keith E. Gubbins} } @article {23, title = {Mesoscopic Monte Carlo simulations of microstructure and conductivity of zirconia-based ceramics}, journal = {J. Eur. Ceram. Soc.}, volume = {61}, year = {2013}, month = {Aug-2013}, pages = {5018-5025}, abstract = {

Zirconia-based refractories are ceramics that serve as furnaces for the production of high-quality speciality glasses. These materials are obtained by cooling a melt composed of different oxides and oxide precursors. The microstructure of these refractories consists of monoclinic zirconia embedded in a three-dimensional interconnected amorphous phase. Using mesoscopic Monte Carlo simulations, the present paper addresses the effect of the amount of amorphous phase and temperature on the microstructure of the material. The simulated microstructures resemble those obtained using tomography experiments. A theoretical model describing the electrical behavior of the material as a function of temperature and composition is also reported. In this model, the conductivity of the ZrO2 particles is assumed to be constant, but the overall conductivity of the sample depends on its tortuosity s. Comparison with experimental data suggests that the present model provides a realistic picture of the electrical behavior of zirconia-based ceramics and leads to quantitative predictions.

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}, doi = {10.1016/j.actamat.2013.04.044}, author = {P. Epicoco and Benoit A. Coasne and A. Gioia and P. Papet and I. Cabodi and M. Gaubil} } @article {76, title = {Molecular intermittent dynamics of interfacial water: probing adsorption and bulk confinement}, journal = {Soft Matter}, volume = {9}, year = {2013}, month = {Jul-26-2013}, pages = {8654-8663}, type = {Article}}, abstract = {

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

}, issn = {1744-683X}, doi = {10.1039/c3sm51940f}, author = {Pierre E. Levitz and Patrick A Bonnaud and Pierre-Andre Cazade and Roland Jean-Marc Pellenq and Benoit A. Coasne} } @article {103, title = {On the molecular origin of high-pressure effects in nanoconfinement: The role of surface chemistry and roughness}, journal = {Journal of Chemical Physics}, volume = {139}, year = {2013}, month = {Oct-14-2013}, type = {Article}, abstract = {

Experiments and simulations both suggest that the pressure experienced by an adsorbed phase confined within a carbon nanoporous material can be several orders of magnitude larger than the bulk phase pressure in equilibrium with the system. To investigate this pressure enhancement, we report a molecular-simulation study of the pressure tensor of argon confined in slit-shaped nanopores with walls of various models, including carbon and silica materials. We show that the pressure is strongly enhanced by confinement, arising from the effect of strongly attractive wall forces; confinement within purely repulsive walls does not lead to such enhanced pressures. Simulations with both the Lennard-Jones and Barker-Fisher-Watts intermolecular potentials for argon-argon interactions give rise to similar results. We also show that an increase in the wall roughness significantly decreases the in-pore pressure due to its influence on the structure of the adsorbate. Finally, we demonstrate that the pressures calculated from the mechanical (direct pressure tensor calculations) and the thermodynamic (volume perturbation method) routes yield almost identical results, suggesting that both methods can be used to calculate the local pressure tensor components in the case of these planar geometries. (C) 2013 AIP Publishing LLC.

}, issn = {0021-9606}, doi = {10.1063/1.4824125}, author = {Yun Long and Jeremy C. Palmer and Benoit A. Coasne and Malgorzata Sliwinska-Bartkowiak and George Jackson and Erich A. Mueller and Keith E. Gubbins} } @article {34, title = {Molecular simulation of adsorption and transport in hierarchical porous materials}, journal = {Langmuir}, volume = {29}, year = {2013}, month = {May-29-2013}, pages = {7864{\textendash}7875}, abstract = {

\<\>Abstract Image

Adsorption and transport in hierarchical porous solids with micro- (\∼1 nm) and mesoporosities (\>2 nm) are investigated by molecular simulation. Two models of hierarchical solids are considered: microporous materials in which mesopores are carved out (model A) and mesoporous materials in which microporous nanoparticles are inserted (model B). Adsorption isotherms for model A can be described as a linear combination of the adsorption isotherms for pure mesoporous and microporous solids. In contrast, adsorption in model B departs from adsorption in pure microporous and mesoporous solids; the inserted microporous particles act as defects, which help nucleate the liquid phase within the mesopore and shift capillary condensation toward lower pressures. As far as transport under a pressure gradient is concerned, the flux in hierarchical materials consisting of microporous solids in which mesopores are carved out obeys the Navier\–Stokes equation so that Darcy\’s law is verified within the mesopore. Moreover, the flow in such materials is larger than in a single mesopore, due to the transfer between micropores and mesopores. This nonzero velocity at the mesopore surface implies that transport in such hierarchical materials involves slippage at the mesopore surface, although the adsorbate has a strong affinity for the surface. In contrast to model A, flux in model B is smaller than in a single mesopore, as the nanoparticles act as constrictions that hinder transport. By a subtle effect arising from fast transport in the mesopores, the presence of mesopores increases the number of molecules in the microporosity in hierarchical materials and, hence, decreases the flow in the micropores (due to mass conservation). As a result, we do not observe faster diffusion in the micropores of hierarchical materials upon flow but slower diffusion, which increases the contact time between the adsorbate and the surface of the microporosity.

}, doi = {10.1021/la401228k}, author = {Benoit A. Coasne and Anne Galarneau and Gerardin, Corine and Fajula, Fran{\c c}ois and Fran{\c c}ois Villemot} } @article {30, title = {Nanofluidic Osmotic Diodes: Theory and Molecular Dynamics Simulations}, journal = {Physical Review Letters}, volume = {111}, year = {2013}, month = {Dec-2013}, pages = {244501}, abstract = {

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

Figure

Figure

Figure

Figure

}, doi = {10.1103/PhysRevLett.111.244501}, author = {Picallo, Clara B and Simon Gravelle and Joly, Laurent and Charlaix, Elisabeth and Lyd{\'e}ric Bocquet} } @article {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} } @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 {61, title = {Role of temperature in the formation and growth of gold monoatomic chains: A molecular dynamics study}, journal = {Physical Review B}, volume = {88}, year = {2013}, month = {Dec-31-2013}, pages = {235438}, abstract = {

The effect of temperature on the formation and growth of monoatomic chains is investigated by extensive molecular dynamics simulations using a semiempirical potential based on the second-moment approximation to the tight-binding Hamiltonian. Gold nanowires, with an aspect ratio of \∼13 and a cross section of \∼1 nm2, are stretched at a rate of 3 m/s in the range of temperatures 5\–600 K with 50 initial configurations per temperature. A detailed study on the probability to form monoatomic chains (MACs) is presented. Two domains are apparent in our simulations: one at T\<100 K, where MACs develop from crystalline disorder at the constriction, and the other at T\>100 K, where MACs form as a consequence of plastic deformation of the nanowire. Our results show that the average length of the formed MACs maximizes at T=150\ K, which is supported by simple energy arguments.

Figure

Figure

Figure

Figure

Figure

}, doi = {10.1103/PhysRevB.88.235438}, author = {Robinson Cortes-Huerto and T. Sondon and Andres Sa{\`u}l} } @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} } @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 {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 {260, title = {Quantifying plasticity-independent creep compliance and relaxation of viscoelastoplastic materials under contact loading}, journal = {Journal of Materials Research}, volume = {27}, year = {2012}, month = {Jan-2012}, pages = {302 - 312}, abstract = {

Here we quantify the time-dependent mechanical properties of a linear viscoelastoplastic material under contact loading. For contact load relaxation, we showed that the relaxation modulus can be measured independently of concurrent plasticity exhibited during the loading phase. For indentation creep, we showed that the rate of change of the contact creep compliance can be measured independently of any plastic deformation exhibited during loading through , where a(t) is the contact radius, h(t) is the displacement of the contact probe, and Pmax is the constant applied load during the creep phase. These analytical relations were compared with numerical simulations of conical indentation creep for a viscoelastoplastic material and validated against sharp indentation creep experiments conducted on polystyrene. The derived relations enable extraction of viscoelastic material characteristics, even if sharp probes confer concurrent plasticity, applicable for a general axisymmetric contact probe geometry and a general time-independent plasticity.

}, issn = {0884-2914}, doi = {10.1557/jmr.2011.302}, author = {Matthieu Vandamme and Tweedie, Catherine A. and Constantinides, Georgios and Franz-Josef Ulm and Krystyn J. Van Vliet} } @article {49, title = {Solvated calcium ions in charged silica nanopores}, journal = {The Journal of Chemical Physics}, volume = {137}, year = {2012}, month = {Aug-14-2012}, pages = {Article Number: 064706}, abstract = {

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

Image of FIG. 1.

Image of FIG. 2.

Image of FIG. 3.

Image of FIG. 4.

Image of FIG. 5.

Image of FIG. 6.

}, doi = {10.1063/1.4742854}, author = {Patrick A Bonnaud and Benoit A. Coasne and Roland Jean-Marc Pellenq} } @article {93, title = {Thermodynamics of Water Confined in Porous Calcium-Silicate-Hydrates}, journal = {Langmuir}, volume = {28}, year = {2012}, month = {Aug-07-2012}, pages = {11422-11432}, type = {Article}, abstract = {
Abstract Image

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

}, issn = {0743-7463}, doi = {10.1021/la301738p}, author = {Patrick A Bonnaud and Qing Ji and Benoit A. Coasne and Roland Jean-Marc Pellenq and Krystyn J. Van Vliet} } @article {289, title = {An atomistic modelling of the porosity impact on UO2 matrix macroscopic properties}, journal = {Journal of Nuclear Materials}, volume = {415}, year = {2011}, month = {Aug-15-2011}, pages = {210 - 216}, abstract = {

The porosity impact on the UO2 matrix thermomechanical properties was investigated using atomistic simulation techniques. The porosity modifies the thermal expansion coefficient and this is attributed to pore surface effects. The elastic moduli at 0\ K and at finite temperature decrease with porosity, this variation being well approximated using affine functions. These results agree with other mesoscale model predictions and experimental data, showing the ability of the semiempirical potential atomistic simulations to give an overall good description of the porous UO2. However, the surface effects are incompletely described.

Fig. 1. The UO2 elementary cell contains 12 atoms: 4 uranium atoms (large spheres){\textellipsis}

fig.=

Fig. 3. Example of 6{\texttimes}6{\texttimes}6 one pore relaxed supercells of different pore radius (4, 6 and{\textellipsis}

Fig. 4. One layer of UO2 as considered in the present work: top {\textendash} the (100){\textellipsis}

Fig. 5. Variation of the UO2 thermal expansion coefficient versus temperature: top {\textendash}{\textellipsis}

Fig. 6. Variation of the shear modulus (G) and Young{\textquoteright}s modulus (E) versus porosity at 0K

}, issn = {00223115}, doi = {10.1016/j.jnucmat.2011.06.006}, author = {Andrei Jelea and Colbert, M. and F. Ribeiro and G. Tr{\'e}glia and Roland Jean-Marc Pellenq} } @proceedings {349, title = {Creep behaviour of confined layers of polyhedral grains}, journal = {2nd International Conference on Particle-Based Methods - Fundamentals and Applications (Particles)}, volume = {PARTICLE-BASED METHODS II: FUNDAMENTALS AND APPLICATIONS }, year = {2011}, month = {Oct-2011}, pages = {574-583}, address = {OCT 26-28 2011 Barcelona, SPAIN}, abstract = {

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

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

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

}, isbn = {978-94-007-1420-5}, issn = {1866-8755}, doi = {10.1007/978-94-007-1421-2_32}, author = {Rafik Aff{\`e}s and Vincent Topin and Jean-Yves Delenne and Yann Monerie}, editor = {St{\'e}phane Bonelli and Dascalu, Cristian and Fran{\c c}ois Nicot} } @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} }