@article {589, title = {Role of Interfaces in Elasticity and Failure of Clay{\textendash}Organic Nanocomposites: Toughening upon Interface Weakening?}, journal = {Langmuir}, volume = {33}, year = {2017}, month = {Oct-24-2017}, pages = {11457 - 11466}, abstract = {

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

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

}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.7b01071}, url = {http://pubs.acs.org/doi/10.1021/acs.langmuir.7b01071}, author = {Gy{\"o}rgy Hantal and Brochard, Laurent and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Benoit A. Coasne} } @article {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 {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 {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 {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} } @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 = {
Abstract Image

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 = {
Abstract Image

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} } @article {142, title = {Optimized molecular reconstruction procedure combining hybrid reverse Monte Carlo and molecular dynamics}, journal = {The Journal of Chemical Physics}, volume = {142}, year = {2015}, month = {Mar-21-2015}, pages = {Article Number: 114112}, abstract = {

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

Image of FIG. 1.

Image of FIG. 2.

Image of FIG. 3.

Image of FIG. 4.

Image of FIG. 5.

Image of FIG. 6.

Image of FIG. 7.

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

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

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

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

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

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

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

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

Image for unlabelled figure

}, 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 = {
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.} } @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.

Figure 1

Figure 2

Figure 3

Figure 4

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 {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 {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 {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.

Image of FIG. 1.
Image of FIG. 2.
Image of FIG. 3.
Image of FIG. 4.
Image of FIG. 5.
Image of FIG. 6.
}, 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 {86, title = {Surface of glassy GeS2: A model based on a first-principles approach}, journal = {Physical Review B}, volume = {90}, year = {2014}, month = {Jul-2014}, type = {Article}, chapter = {045423}, abstract = {

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

Figure

Figure

Figure

Figure

Figure

Figure

Figure

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

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

}, issn = {0743-7463}, doi = {10.1021/la404166y}, author = {Tourne-Peteilh, Corine and Benoit A. Coasne and In, Martin and Brevet, David and Devoisselle, Jean-Marie and Andre Vioux and Lydie Viau} } @article {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} } @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} } @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.

Image for unlabelled figure

}, 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 {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} } @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} }