Showing papers by "Benoit Coasne published in 2011"
TL;DR: A molecular simulation study of the pressure tensor of an argon nanophase within slit-shaped carbon pores is reported and it is shown that the tangential pressure is positive and large, while the normal pressure can be positive or negative depending on pore width.
Abstract: Phenomena that occur only at high pressures in bulk phases are often observed in nanopores, suggesting that the pressure in such confined phases is large. We report a molecular simulation study of the pressure tensor of an argon nanophase within slit-shaped carbon pores and show that the tangential pressure is positive and large, while the normal pressure can be positive or negative depending on pore width. We also show that small changes in the bulk pressure have a large effect on the tangential pressure, suggesting that it should be possible to control the latter over wide ranges in laboratory experiments.
124 citations
TL;DR: The adsorption of carbon dioxide and methane in nanoporous carbons in the presence of water is studied and typical molecular configurations obtained indicate that the water molecules form isolated clusters within the host porous carbon due to the nonfavorable interaction between carbon dioxide or methane and water.
Abstract: The adsorption of carbon dioxide and methane in nanoporous carbons in the presence of water is studied using experiments and molecular simulations. For all amounts of adsorbed water molecules, the adsorption isotherms for carbon dioxide and methane resemble those obtained for pure fluids. The pore filling mechanism does not seem to be affected by the presence of the water molecules. Moreover, the pressure at which the maximum adsorbed amount of methane or carbon dioxide is reached is nearly insensitive to the loading of preadsorbed water molecules. In contrast, the adsorbed amount of methane or carbon dioxide decreases linearly with the number of guest water molecules. Typical molecular configurations obtained using molecular simulation indicate that the water molecules form isolated clusters within the host porous carbon due to the nonfavorable interaction between carbon dioxide or methane and water.
113 citations
TL;DR: Molecular simulations of a silica nanopore that is gradually filled with a typical imidazolium salt ionic liquid are reported to obtain a realistic model of these ionogels.
Abstract: An important strategy for using ionic liquids is to immobilize them by impregnation of supports or incorporation into porous solids to obtain materials called “ionogels”. Of considerable importance for applications (electrolyte membranes, supported catalysts, etc.), such confinement results in dramatic changes in the physicochemical properties of the ionic liquid. Here, we report molecular simulations of a silica nanopore that is gradually filled with a typical imidazolium salt ionic liquid to obtain a realistic model of these ionogels. Despite the significant layering and stiffening of the ionic liquid in the vicinity of the silica surface, the pair correlation functions and magnitude of its dynamics clearly evidence liquid-like behavior. An increase in the self-diffusivity and ionic conductivity, associated with a decrease in the characteristic residence times of ions at the silica surface, is observed upon increasing the loading as the ionic liquid fills the nanopore center and tends to recover its bul...
102 citations
TL;DR: A microscopic picture of the deactivation of pressure-induced amorphization by incorporation of molecules is provided, which shows that the adsorption of molecules in the micropores of the material increases its bulk modulus.
Abstract: We report a molecular simulation study of the mechanical properties of microporous zeolites filled with guest molecules. We show that the adsorption of molecules in the micropores of the material increases its bulk modulus. These results provide a microscopic picture of the deactivation of pressure-induced amorphization by incorporation of molecules.
71 citations
TL;DR: In this article, the structure and dynamics of benzene confined at 293 K in silica nanopores of different diameters (D = 2.0 nm and D = 3.6 nm) are investigated by means of grand canonical Monte Carlo and molecular dynamics simulations.
Abstract: The structure and dynamics of benzene confined at 293 K in silica nanopores of different diameters (D = 2.0 nm and D = 3.6 nm) are investigated by means of grand canonical Monte Carlo and molecular dynamics simulations. In order to account in a realistic way for the interactions between benzene and the silica surface, we consider a recent model that accounts for the π-electrons of the aromatic cycle in the benzene molecule. Confined benzene exhibits significant layering and orientational ordering in the vicinity of the silica surface (up to two adsorbed layers) and tends to recover its bulk properties in the pore center. Using suitable order parameters, we show that benzene molecules close to the pore surface tend to have their ring lying flat on the silica surface (and hence perpendicular to the pore axis). Such a preferential parallel orientation with respect to the silica surface suggests that a proper description of the π-electrons of the benzene aromatic ring and its specific Coulombic interaction with the partial charges carried by the silica atoms is crucial. The dynamics of benzene confined in the silica nanopores is always slower than in the bulk. Both the translational and rotational dynamics of confined benzene can be described as a bulklike contribution in the pore center that depends on the pore size and a surface contribution that is nearly insensitive to the pore size. These simulation results are discussed in the light of available experimental data on the structure and dynamics of benzene confined in nanoporous silicas.
55 citations
TL;DR: A hydrophilic to hydrophobic transition appears as the surface becomes purely siliceous as a result of autoirradiation in nuclear waste glass releases hydrogen atoms from silanol groups and can induce such a transition.
Abstract: Realistic models of amorphous silica surfaces with different silanol densities are built using Monte Carlo annealing. Water–silica interfaces are characterized by their energy interaction maps, adsorption isotherms, self-diffusion coefficients, and Poiseuille flows. A hydrophilic to hydrophobic transition appears as the surface becomes purely siliceous. These results imply significant consequences for the description of surfaces. First, realistic models are required for amorphous silica interfaces. Second, experimental amorphous silica hydrophilicity is attributed to charged or uncharged defects, and not to amorphousness. In addition, autoirradiation in nuclear waste glass releases hydrogen atoms from silanol groups and can induce such a transition.
54 citations
TL;DR: The results above show that the adsorption, structure, and dynamics of benzene confined in disordered porous carbons cannot be described in simple terms using an ideal model such as the slit pore geometry.
Abstract: Molecular simulations are used to study the adsorption, structure, and dynamics of benzene at 298 K in atomistic models of ordered and disordered nanoporous carbons. The ordered porous carbon is a regular slit pore made up of graphene sheets. The disordered porous carbon is a structural model that reproduces the morphological (pore shape) and topological (pore connectivity) disorder of saccharose-based porous carbons. As expected for pores of a regular geometry, the filling occurs at well-defined pressures which are an increasing function of the pore width H. In contrast, in qualitative agreement with experimental data for activated carbon fibers, the filling of the disordered carbon is continuous and spans over a large pressure range. The structure and dynamics of benzene in the disordered carbon also strongly depart from that for the slit pore geometry. While benzene in the slit graphite nanopores exhibits significant layering, benzene in the disordered porous carbon exhibits a liquid-like structure very close to its bulk counterpart. Both the ordering and self-diffusivity of benzene in the graphite nanopores depend in a complex manner on the pore width. The dynamics is either slower or faster than its bulk counterpart; our data show that the self-diffusivity decreases as the number of confined layers n divided by the pore width H increases (except for very small pore sizes for which benzene crystallizes and is necessarily slower than the liquid phase). The dynamics of benzene in the disordered porous carbon is isotropic and is much slower than that for the graphite slit nanopores (even with the smallest slit nanopore considered in this work). The results above show that the adsorption, structure, and dynamics of benzene confined in disordered porous carbons cannot be described in simple terms using an ideal model such as the slit pore geometry.
54 citations
TL;DR: In this paper, mesoscopic Monte Carlo simulations of interfacial films in ZnO-Bi2O3 binary ceramics were performed and the authors observed the formation of Bi2O-3-rich interfacial phases at the surface of surface amorphous films or at the grain-boundary between ZnOs grains (intergranular films).
Abstract: This paper reports mesoscopic Monte Carlo simulations (in which a ‘mesoscopic particle’ corresponds to a group of atoms or molecules) of interfacial films in ZnO–Bi2O3 binary ceramics. We observe the formation of Bi2O3-rich interfacial phases at the surface of ZnO grains (surface amorphous films) or at the grain-boundary between ZnO grains (intergranular films). In qualitative agreement with the experimental results reported on premelting of ceramics, the thickness of these films increases as the temperature increases up to the eutectic temperature. Moreover, the Bi2O3 concentration in the surficial or intergranular films is found to be larger than in the bulk. These surficial films exhibit both some layering and lateral ordering.
2 citations