@article {668, title = {Spontaneous rotation can stabilise ordered chiral active fluids}, journal = {Nature Communications}, volume = {10}, year = {2019}, month = {Feb-22-2019}, pages = { Article Number: 920 }, abstract = {

Active hydrodynamic theories are a powerful tool to study the emergent ordered phases of internally driven particles such as bird flocks, bacterial suspension and their artificial analogues. While theories of orientationally ordered phases are by now well established, the effect of chirality on these phases is much less studied. In this paper, we present a complete dynamical theory of orientationally ordered chiral particles in two-dimensional incompressible systems. We show that phase-coherent states of rotating chiral particles are remarkably stable in both momentum-conserved and non-conserved systems in contrast to their non-rotating counterparts. Furthermore, defect separation-which drives chaotic flows in non-rotating active fluids-is suppressed by intrinsic rotation of chiral active particles. We thus establish chirality as a source of dramatic stabilisation in active systems, which could be key in interpreting the collective behaviors of some biological tissues, cytoskeletal systems and collections of bacteria.

}, doi = {10.1038/s41467-019-08914-7}, url = {http://www.nature.com/articles/s41467-019-08914-7}, author = {Maitra, Ananyo and Lenz, Martin} } @article {655, title = {Stress-dependent amplification of active forces in nonlinear elastic media}, journal = {Soft Matter}, volume = {15}, year = {2019}, month = {Jan-14-2019}, pages = {331 - 338}, abstract = {

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

}, issn = {1744-683X}, doi = {10.1039/C8SM00949J}, url = {http://xlink.rsc.org/?DOI=C8SM00949J}, author = {Ronceray, Pierre and Broedersz, Chase P. and Lenz, Martin} } @article {660, title = {Sol{\textendash}gel process and complex fluids: sculpting porous matter at various lengths scales towards the Si(HIPE), Si(PHIPE), and SBA-15-Si(HIPE) series}, journal = {Journal of Sol-Gel Science and Technology}, volume = {18}, year = {2018}, month = {Sep-11-2018}, abstract = {

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

}, issn = {0928-0707}, doi = {10.1007/s10971-018-4794-8}, url = {http://link.springer.com/10.1007/s10971-018-4794-8}, author = {Roucher, Armand and Schmitt, Veronique and Blin, Jean-Luc and Backov, Renal} } @article {611, title = {Surface temperatures in New York City: Geospatial data enables the accurate prediction of radiative heat transfer}, journal = {Scientific Reports}, volume = {8}, year = {2018}, month = {Feb-02-2018}, pages = { Article Number 2224 }, abstract = {

Despite decades of research seeking to derive the urban energy budget, the dynamics of thermal exchange in the densely constructed environment is not yet well understood. Using New York City as a study site, we present a novel hybrid experimental-computational approach for a better understanding of the radiative heat transfer in complex urban environments. The aim of this work is to contribute to the calculation of the urban energy budget, particularly the stored energy. We will focus our attention on surface thermal radiation. Improved understanding of urban thermodynamics incorporating the interaction of various bodies, particularly in high rise cities, will have implications on energy conservation at the building scale, and for human health and comfort at the urban scale. The platform presented is based on longwave hyperspectral imaging of nearly 100 blocks of Manhattan, in addition to a geospatial radiosity model that describes the collective radiative heat exchange between multiple buildings. Despite assumptions in surface emissivity and thermal conductivity of buildings walls, the close comparison of temperatures derived from measurements and computations is promising. Results imply that the presented geospatial thermodynamic model of urban structures can enable accurate and high resolution analysis of instantaneous urban surface temperatures.

}, keywords = {ENERGY-BALANCE; URBAN; STORAGE; MODEL; ALBEDO; FLUX}, doi = {10.1038/s41598-018-19846-5}, url = {http://www.nature.com/articles/s41598-018-19846-5}, author = {Ghandehari, Masoud and Emig, Thorsten and Aghamohamadnia, Milad} } @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 {607, title = {Scaling behavior of immersed granular flows}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 09044}, abstract = {

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

}, doi = {10.1051/epjconf/201714009044}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714009044}, author = {L. Amarsid and Jean-Yves Delenne and Patrick Mutabaruka and Yann Monerie and Perales, F. and Farhang Radja{\"\i}}, editor = {Saeid Nezamabadi and Luding, S.} } @article {605, title = {Small solar system bodies as granular systems}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 14011}, abstract = {

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

}, doi = {10.1051/epjconf/201714014011}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714014011}, author = {Hestroffer, Daniel and Adriano Campo Bagat{\'\i}n and Losert, Wolfgang and Opsomer, Eric and S{\'a}nchez, Paul and Scheeres, Daniel J. and Staron, Lydie and Taberlet, Nicolas and Yano, Hajime and Eggl, Siegfried and Lecomte, Charles-Edouard and Murdoch, Naomi and Farhang Radja{\"\i} and Richardson, Derek C. and Salazar, Marcos and Schwartz, Stephen R. and Tanga, Paolo}, editor = {Saeid Nezamabadi and Luding, S. and Jean-Yves Delenne} } @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 {599, title = {Strength of wet agglomerates of spherical particles: effects of friction and size distribution}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 08021}, abstract = {

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

}, doi = {10.1051/epjconf/201714008021}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714008021}, author = {Vo, Thanh-Trung and Patrick Mutabaruka and Jean-Yves Delenne and Saeid Nezamabadi and Farhang Radja{\"\i}}, editor = {Luding, S.} } @article {593, title = {Stress Transmission and Failure in Disordered Porous Media}, journal = {Physical Review Letters}, volume = {119}, year = {2017}, month = {Aug-14-2017}, pages = { Article Number: 075501 }, abstract = {

By means of extensive lattice-element simulations, we investigate stress transmission and its relation with failure properties in increasingly disordered porous systems. We observe a non-Gaussian broadening of stress probability density functions under tensile loading with increasing porosity and disorder, revealing a gradual transition from a state governed by single-pore stress concentration to a state controlled by multipore interactions and metric disorder. This effect is captured by the excess kurtosis of stress distributions and shown to be nicely correlated with the second moment of local porosity fluctuations, which appears thus as a (dis)order parameter for the system. By generating statistical ensembles of porous textures with varying porosity and disorder, we derive a general expression for the fracture stress as a decreasing function of porosity and disorder. Focusing on critical sites where the local stress is above the global fracture threshold, we also analyze the transition to failure in terms of a coarse-graining length. These findings provide a general framework which can also be more generally applied to multiphase and structural heterogeneous materials.

}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.119.075501}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.119.075501}, author = {Hadrien Laubie and Farhang Radja{\"\i} and Roland Jean-Marc Pellenq and Franz-Josef Ulm} } @article {240, title = {Stress Transmission and Failure in Disordered Porous Media}, journal = {PHYSICAL REVIEW LETTERS}, volume = {119}, year = {2017}, month = {Aug-14-2017}, pages = {Article Number: 075501}, abstract = {

By means of extensive lattice-element simulations, we investigate stress transmission and its relation with failure properties in increasingly disordered porous systems. We observe a non-Gaussian broadening of stress probability density functions under tensile loading with increasing porosity and disorder, revealing a gradual transition from a state governed by single-pore stress concentration to a state controlled by multipore interactions and metric disorder. This effect is captured by the excess kurtosis of stress distributions and shown to be nicely correlated with the second moment of local porosity fluctuations, which appears thus as a (dis)order parameter for the system. By generating statistical ensembles of porous textures with varying porosity and disorder, we derive a general expression for the fracture stress as a decreasing function of porosity and disorder. Focusing on critical sites where the local stress is above the global fracture threshold, we also analyze the transition to failure in terms of a coarse-graining length. These findings provide a general framework which can also be more generally applied to multiphase and structural heterogeneous materials.

Figure

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Figure

}, doi = {10.1103/PhysRevLett.119.075501}, author = {Hadrien Laubie and Farhang Radja{\"\i} and Roland Jean-Marc Pellenq and et al} } @article {270, title = {Scaling behaviour of cohesive granular flows}, journal = {EPL (Europhysics Letters)}, volume = {112}, year = {2016}, month = {Jan-12-2016}, pages = {Article Number: 64004}, abstract = {

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

}, issn = {0295-5075}, doi = {10.1209/0295-5075/112/64004}, author = {Berger, Nicolas and Emilien Az{\'e}ma and Douce, Jean-Fran{\c c}ois and Farhang Radja{\"\i}} } @article {585, title = {Simultaneous Rheoelectric Measurements of Strongly Conductive Complex Fluids}, journal = {Physical Review Applied}, volume = {6}, year = {2016}, month = {Dec-09-2016}, pages = { Article Number: 064004 }, abstract = {

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

}, doi = {10.1103/PhysRevApplied.6.064004}, url = {https://link.aps.org/doi/10.1103/PhysRevApplied.6.064004}, author = {Helal, Ahmed and Divoux, Thibaut and McKinley, Gareth H.} } @article {319, title = {Size-Effect Law for Scratch Tests of Axisymmetric Shape}, journal = {Journal of Engineering Mechanics}, volume = {142}, year = {2016}, month = {Dec-2016}, pages = {Article Number: 04016094 }, abstract = {

This paper presents a theoretical and experimental framework for the application of size-effect analysis to microscratch testing as a means to quantify the fracture properties and internal friction of materials at the microscale. The energetic size-effect law (SEL) for microscratch tests is developed for a general monomeric probe shape in terms of an intrinsic size function. The fundamental idea of the proposed approach is to rescale the scratch response to that of the flat punch, a conjecture that allows one to compare the SEL for different probe geometries, and thus solve for the asymptotic fracture toughness and effective process zone length from scratch tests done on homogenous (acetal homopolymer resin and polycarbonate resin) and inhomogeneous materials (mica ceramic and gas shale). As a material of current interest for controlled fracture studies, two samples of gas shale cored from the Marcellus and Eagle Ford formations are tested and analyzed to quantify all material properties that may be derived from the scratch resistance; namely fracture parameters, asymptotic hardness, strength, cohesion, and internal friction.

}, issn = {0733-9399}, doi = {10.1061/(ASCE)EM.1943-7889.0001159}, author = {Hubler, Mija H. and Franz-Josef Ulm} } @article {619, title = {Spectroscopic probe of the van der Waals interaction between polar molecules and a curved surface}, journal = {Physical Review A}, volume = {94}, year = {2016}, month = {Aug-17-2016}, abstract = {

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

}, issn = {2469-9926}, doi = {10.1103/PhysRevA.94.022509}, url = {https://link.aps.org/doi/10.1103/PhysRevA.94.022509}, author = {Bimonte, Giuseppe and Emig, Thorsten and Jaffe, R. L. and Kardar, Mehran} } @proceedings {329, title = {Shrinkage Due to Colloidal Force Interactions}, journal = {10th International Conference on Mechanics and Physics of Creep, Shrinkage, and Durability of Concrete and Concrete Structures CONCREEP 10}, volume = {CONCREEP 10: MECHANICS AND PHYSICS OF CREEP, SHRINKAGE, AND DURABILITY OF CONCRETE AND CONCRETE STRUCTURES}, year = {2015}, month = {Sep-17-2015}, pages = {13-16}, publisher = {American Society of Civil Engineers}, address = {September 21{\textendash}23, 2015, Vienna, AustriaReston, VA }, abstract = {

It has long been argued that shrinkage in cementitious materials can occur even in the absence of drying phenomena. Herein we argue that such shrinkage is attributable to colloidal forces that develop between C-S-H particles during the hydration in an out-of-equilibrium process. We base our argument on meso-scale simulation results, and show via microporomechanics theory that such colloidal forces can lead to the build-up of solid eigenstresses causing macroscopic shrinkage deformation.

}, doi = {10.1061/978078447934610.1061/9780784479346.002}, author = {Franz-Josef Ulm and Roland Jean-Marc Pellenq}, editor = {Hellmich, Christian and Pichler, Bernhard and Kollegger, Johann} } @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 = {
Abstract Image

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.} } @book {647, title = {Springer Series in Materials ScienceMolecular Dynamics Simulations of Disordered MaterialsFirst-Principles Modeling of Binary Chalcogenides: Recent Accomplishments and New Achievements}, volume = {215}, year = {2015}, pages = {313 - 344}, publisher = {Springer International Publishing}, organization = {Springer International Publishing}, address = {Cham}, abstract = {

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

}, isbn = {978-3-319-15674-3}, issn = {0933-033X}, doi = {10.1007/978-3-319-15675-010.1007/978-3-319-15675-0_12}, url = {http://link.springer.com/10.1007/978-3-319-15675-0}, author = {Bouzid, A. and Le Roux, S. and Guido Ori and Tugene, Christine and Boero, M. and Carlo Massobrio}, editor = {Carlo Massobrio and Du, Jincheng and Bernasconi, Marco and Salmon, Philip S.} } @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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Figure 5

Figure 6

}, issn = {2041-1723}, doi = {10.1038/ncomms7949}, author = {Kerstyn I. Falk and Benoit A. Coasne and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Lyd{\'e}ric Bocquet} } @article {304, title = {Scaling Relationships of Dissipation-Induced Pavement-Vehicle Interactions}, journal = {Transportation Research Record: Journal of the Transportation Research Board}, volume = {2457}, year = {2014}, month = {Jan-2014}, pages = {95 - 104}, abstract = {

Rolling resistance is one of the key factors that affect the fuel efficiency of the national pavement system. In addition to pavement texture and pavement roughness, the dissipation of mechanical work provided by the vehicle because of viscous deformation within the pavement structure has been recognized as a relevant factor contributing to the environmental footprint of pavement systems. This dissipation depends on material and structural parameters that can be optimized to increase the fuel efficiency of pavements. Identifying the key material and structural parameters that drive this dissipation is the focus of this paper. This identification is achieved by a combination of dimensional analysis and model-based simulations of the dissipation of a viscoelastic beam on an elastic foundation. For linear viscoelastic systems, the dissipation is found to scale with the square of the vehicle weight and with the inverse of the viscous relaxation time, in addition to distinct power relations of top-layer stiffness, thickness, and subgrade modulus. These scaling relations can be used by pavement engineers to reduce such pavement-inherent dissipation mechanisms and increase the fuel efficiency of a pavement design. An example shows the application of these scaling relations with data extracted from FHWA\&$\#$39;s Long-Term Pavement Performance database for seven road classes. The scaling relations provide a means for evaluating the performance of the various road classes in terms of the fuel efficiency related to dissipation.

}, issn = {0361-1981}, doi = {10.3141/2457-10}, author = {Arghavan Louhghalam and Mehdi Akbarian and Franz-Josef Ulm} } @article {300, title = {Scratch hardness-strength solutions for cohesive-frictional materials}, journal = {International Journal for Numerical and Analytical Methods in Geomechanics}, volume = {36}, year = {2014}, month = {Feb-25-2014}, pages = {307 - 326}, abstract = {

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

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

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

}, url = {http://prodinra.inra.fr/record/369542}, author = {L. Amarsid and Patrick Mutabaruka and Jean-Yves Delenne}, editor = {Kenichi Soga and Krishna Kumar and Giovanna Biscontin} } @article {110, title = {Simultaneous assessment of phase chemistry, phase abundance and bulk chemistry with statistical electron probe micro-analyses: Application to cement clinkers}, journal = {Cement and concrete Research}, volume = {55}, year = {2014}, month = {Jan-2014}, pages = {35-48}, type = {Article}, abstract = {

According to recent developments in cement clinker engineering, the optimization of chemical substitutions in the main clinker phases offers a promising approach to improve both reactivity and grindability of clinkers. Thus, monitoring the chemistry of the phases may become part of the quality control at the cement plants, along with the usual measurements of the abundance of the mineralogical phases (quantitative X-ray diffraction) and the bulk chemistry (X-ray fluorescence). This paper presents a new method to assess these three complementary quantities with a single experiment. The method is based on electron microprobe spot analyses, performed over a grid located on a representative surface of the sample and interpreted with advanced statistical tools. This paper describes the method and the experimental program performed on industrial clinkers to establish the accuracy in comparison to conventional methods. (C) 2013 Elsevier Ltd. All rights reserved.

SEM micrographs of coarsely ground sample C-C4. (a) The 500{\texttimes} magnification ...
Ca vs. Si representation for bulk samples (a) B-C2 focused on the entire range ...
(a) SEM micrograph of clinker C4 at 1000{\texttimes} magnification: the spacing between ...
Additional representations of the clustered results for bulk samples: Fe vs. Si ...
Si vs. Ca representation for coarsely ground samples (a) C-C2a and (b) C-C4b and ...
}, keywords = {Characterization, Clinker, EPMA, X-ray diffraction}, issn = {0008-8846}, doi = {10.1016/j.cemconres.2013.09.013}, author = {Wilson, William and Konrad J. Krakowiak and Franz-Josef Ulm} } @article {261, title = {A soft matter in construction {\textendash} Statistical physics approach to formation and mechanics of C{\textendash}S{\textendash}H gels in cement}, journal = {The European Physical Journal Special Topics}, volume = {223}, year = {2014}, month = {Oct-2014}, pages = {2285 - 2295}, abstract = {

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

}, issn = {1951-6355}, doi = {10.1140/epjst/e2014-02264-1}, author = {Emanuela Del Gado and Katerina Ioannidou and Enrico Masoero and Alain Baronnet and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Sidney Yip} } @article {276, title = {Some micromechanical aspects of failure in granular materials based on second-order work}, journal = {Comptes Rendus M{\'e}canique}, volume = {342}, year = {2014}, month = {Mar-2014}, pages = {174 - 188}, abstract = {

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

}, issn = {16310721}, doi = {10.1016/j.crme.2014.01.006}, author = {Fran{\c c}ois Nicot and Hadda, Nejib and Sibille, Luc and Farhang Radja{\"\i} and Hicher, Pierre-Yves and Darve, F{\'e}lix} } @article {310, title = {Stimuli-Responsive Cement-Reinforced Rubber}, journal = {ACS Applied Materials \& Interfaces}, volume = {6}, year = {2014}, month = {May-14-2014}, pages = {6962 - 6968}, abstract = {
Abstract Image

In this work, we report the successful development of a cement\–rubber reactive composite with reversible mechanical properties. Initially, the composite behaves like rubber containing inert filler, but when exposed to water, it increases in volume and reaches a stiffness that is intermediate between that of hydrogenated nitrile butadiene rubber (HNBR) and hydrated cement, while maintaining a relatively large ductility characteristic of rubber. After drying, the modulus increases even further up to 400 MPa. Wet/drying cycles prove that the elastic modulus can reversibly change between 150 and 400 MPa. Utilizing attenuated total reflection Fourier transform infrared spectroscopy), we demonstrate that the high pH produced by the hydration of cement triggers the hydrolysis of the rubber nitrile groups into carboxylate anions. Thus, the salt bridges, generated between the carboxylate anions of the elastomer and the cations of the filler, are responsible for the reversible variations in volume and elastic modulus of the composite as a consequence of environmental moisture exposure. These results reveal that cement nanoparticles can successfully be used to accomplish a twofold task: (a) achieve an original postpolymerization modification that allows one to work with carboxylate HNBR (HXNBR) not obtained by direct copolymerization of carboxylate monomers with butadiene, and (b) synthesize a stimuli-responsive polymeric composite. This new type of material, having an ideal behavior for sealing application, could be used as an alternative to cement for oil field zonal isolation applications.

}, issn = {1944-8244}, doi = {10.1021/am500774k}, author = {Musso, Simone and Robisson, Agathe and Sudeep Maheshwar and Franz-Josef Ulm} } @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 {67, title = {Sub-additive ionic transport across arrays of solid-state nanopores}, journal = {Physics of Fluids (1994-present)}, volume = {26}, year = {2014}, month = {Jan-31-2014}, pages = {012005}, abstract = {

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

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}, doi = {10.1063/1.4863206}, author = {Gadaleta, A and Sempere, C and Simon Gravelle and A. Siria and Fulcrand, R and Christophe Ybert and Lyd{\'e}ric Bocquet} } @article {32, title = {Surface Chemistry and Atomic-Scale Reconstruction of Kerogen-Silica Composites}, journal = {The Journal of Physical Chemistry C}, volume = {118}, year = {2014}, month = {Feb-6-2014}, pages = {2429-2438}, abstract = {
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Interest in gas shale, a novel source rock of natural gas, has increased tremendously in recent years. Better understanding of the kerogen\–rock interaction is of crucial importance for efficient gas extraction and, hence, asset management. In this study, we explore the possible chemical bonds between kerogen and silica, one of the most predominant mineral constituents of gas shale, by means of quantum chemistry. Energetically favorable bond formation reactions are found between alcoholic hydroxyl, carboxylate, and aldehyde groups, as well as aliphatic double bonds of kerogen and the silica surface. The performance of a reactive force field was also assessed in a representative set of chemical reactions and found to be satisfactory. The potential impact of bond formation reactions between the two phases on the actual kerogen\–silica interface is discussed as a function of the kerogen type, maturity, and density. Finally, a methodology aiming to reconstruct realistic kerogen\–silica interfaces is presented.

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

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

Figure

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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} } @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 {60, title = {Simple views on surface stress and surface energy concepts}, journal = {Advances in Natural Sciences: Nanoscience and Nanotechnology}, volume = {5}, year = {2013}, month = {Nov-27-2013}, pages = {013002}, abstract = {

Some aspects of the thermodynamics and mechanics of solid surfaces, in particular with respect to surface stress and surface energy, are reviewed. The purpose is to enlighten the deep differences between these two physical quantities. We consider successively the case of atomic flat surfaces and the case of vicinal surfaces characterized by surface stress discontinuities. Finally, experimental examples, concerning Si surfaces, are described.

}, doi = {10.1088/2043-6262/5/1/013002}, author = {M{\"u}ller, Pierre and Andres Sa{\`u}l and Leroy, Fr{\'e}d{\'e}ric} } @article {220, title = {Strength Homogenization of Double-Porosity Cohesive-Frictional Solids}, journal = {Journal of Applied Mechanics}, volume = {80}, year = {2013}, month = {Mar-2013}, pages = {Article Number: 020902}, abstract = {

The strength homogenization of cohesive-frictional solids influenced by the presence of two pressurized pore spaces of different characteristic sizes is addressed in this study. A two-scale homogenization model is developed based on limit analysis and the second-order method (SOM) in linear comparison composite theory, which resolves the nonlinear strength behavior through the use of linear comparison composites with optimally chosen properties. For the scale of the classical configuration of a porous solid, the formulation employs a compressible thermoelastic comparison composite to deliver closed-form expressions of strength criteria. Comparisons with numerical results reveal that the proposed homogenization estimates for drained conditions are adequate except for high triaxialities in the mean compressive strength regime. At the macroscopic scale of the double-porosity material, the SOM results are in agreement with strength criteria predicted by alternative micromechanics solutions for materials with purely cohesive solid matrices and drained conditions. The model predictions for the cohesive-frictional case show that drained strength development in granularlike composites is affected by the partitioning of porosity between micro-and macropores. In contrast, the drained strength is virtually equivalent for single-and double-porosity materials with matrix-inclusion morphologies. Finally, the second-order linear comparison composite approach confirms the applicability of an effective stress concept, previously proposed in the literature of homogenization of cohesive-frictional porous solids, for double-porosity materials subjected to similar pressures in the two pore spaces. For dissimilar pore pressures, the model analytically resolves the complex interplays of microstructure, solid properties, and volume fractions of phases, which cannot be recapitulated by the effective stress concept.

}, issn = {0021-8936}, doi = {10.1115/1.4007905}, author = {J. Alberto Ortega and Franz-Josef Ulm} } @article {53, title = {Set in stone? A perspective on the concrete sustainability challenge}, journal = {MRS bulletin}, volume = {37}, year = {2012}, month = {Apr-09-2012}, pages = {395{\textendash}402}, abstract = {

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

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

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

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Image of FIG. 6.

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

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

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

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

}, doi = {10.1504/IJNT.2012.045335 }, author = {Christophe Bichara and Marsal, P and Mottet, C and Roland Jean-Marc Pellenq and F. Ribeiro and Andres Sa{\`u}l and G. Tr{\'e}glia and Weissker, H{\textendash}Ch} } @article {256, title = {The scratch test for strength and fracture toughness determination of oil well cements cured at high temperature and pressure}, journal = {Cement and Concrete Research}, volume = {41}, year = {2011}, month = {sept-2011}, pages = {942 - 946}, abstract = {

Recent advances in scratch test analysis provide new ways to relate measured scratch test properties not only to strength properties but fracture properties of materials as well. Herein, we present an application of such tools to oil well cements cured at high temperatures and pressures. We find a concurrent increase of strength and toughness of different oil well cement baseline formulations which we relate to the water-to-binder ratio for a series of cementitious materials prepared with cement and silica flour. The scratch test thus emerges as a self-consistent technique for both cohesive\–frictional strength and fracture properties that is highly reproducible, almost non-destructive, and not more sophisticated than classical compression tests, which makes this \‘old\’ test highly attractive for performance-based field applications.

}, issn = {00088846}, doi = {10.1016/j.cemconres.2011.04.014}, author = {Franz-Josef Ulm and James, Simon} } @article {254, title = {Scratch test model for the determination of fracture toughness}, journal = {Engineering Fracture Mechanics}, volume = {78}, year = {2011}, month = {Jan-2011}, pages = {334 - 342}, abstract = {

We revisit the scratch test within the framework of linear elastic fracture mechanics. In the analysis, we employ an Airy stress function approach to determine stresses and displacement in the vicinity of the scratch-blade\–material interface, which serve as input for the evaluation of the energy release rate by means of the J-Integral. In contrast to previous models, the energy release rate thus found scales with the sum of the applied forces squared. This entails a linear relation between the applied forces and , where w is the scratch width and d the scratch depth. This analytical scaling is validated using experimental scratch data on cement paste and sandstone, which shows that the proposed approach provides a convenient way to determine the fracture toughness from scratch tests carried out with different scratch widths and depths

}, issn = {00137944}, doi = {10.1016/j.engfracmech.2010.09.017}, author = {Ange-Therese Akono and Franz-Josef Ulm} } @article {255, title = {Scratching as a Fracture Process: From Butter to Steel}, journal = {Physical Review Letters}, volume = {106}, year = {2011}, month = {May-20-2011}, pages = {Article Number: 204302}, abstract = {

We present results of a hybrid experimental and theoretical investigation of the fracture scaling in scratch tests and show that scratching is a fracture dominated process. Validated for paraffin wax, cement paste, Jurassic limestone and steel, we derive a model that provides a quantitative means to relate quantities measured in scratch tests to fracture properties of materials at multiple scales. The scalability of scratching for different probes and depths opens new venues towards miniaturization of our technique, to extract fracture properties of materials at even smaller length scales.

Figure

Figure

Figure

Figure

}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.106.204302}, author = {Ange-Therese Akono and Reis, P. M. and Franz-Josef Ulm} } @proceedings {364, title = {Springer Series in Geomechanics and Geoengineering Multiscale and Multiphysics Processes in Geomechanics SIMULATION OF HYDRATION AND ELASTIC PROPERTIES OF MONTMORILLONITE USING MOLECULAR DYNAMICS}, journal = {International Workshop on Multiscale and Multiphysics Processes in Geomechanics}, volume = {Springer Series in Geomechanics and Geoengineering}, year = {2011}, month = {2011}, pages = {105 - 108}, publisher = {Springer Berlin Heidelberg}, address = {JUN 23-25 2010 Stanford Univ, Stanford, CA}, abstract = {

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

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

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

}, isbn = {978-3-642-19629-4}, issn = {1866-8755}, doi = {10.1007/978-3-642-19630-0_15}, author = {J. Alberto Ortega and Gathier, Benjamin and Franz-Josef Ulm}, editor = {Wu, Wei and Borja, Ronaldo I.} } @proceedings {355, title = {Stress fields in granular solids: Effect of composition}, journal = {Symposium on Science and Technology of Powders and Sintered Materials (STPMF 2009)}, volume = {POWDER TECHNOLOGY}, year = {2011}, month = {Mar-25-2011}, pages = {568 - 573}, address = {MAY 25-27 2009 Montpellier, FRANCE}, abstract = {

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

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