Showing papers by "Benoit Coasne published in 2010"
TL;DR: This paper reports on a molecular simulation study of the thermodynamics, structure and dynamics of water confined at ambient temperature in hydroxylated silica nanopores of a width H = 10 and 20 Å, indicating that water molecules within the first adsorbed layer tend to adopt a H-down orientation with respect to the silica substrate and suggesting that the self-diffusivity of confined water is sensitive to the Adsorbed amount.
Abstract: This paper reports on a molecular simulation study of the thermodynamics, structure and dynamics of water confined at ambient temperature in hydroxylated silica nanopores of a width H = 10 and 20 A. The adsorption isotherms for water in these nanopores resemble those observed for experimental samples; the adsorbed amount increases continuously in the multilayer adsorption regime until a jump occurs due to capillary condensation of the fluid within the pore. Strong layering of water in the vicinity of the silica surfaces is observed as marked density oscillations are observed up to 8 A from the surface in the density profiles for confined water. Our results indicate that water molecules within the first adsorbed layer tend to adopt a H-down orientation with respect to the silica substrate. For all pore sizes and adsorbed amounts, the self-diffusivity of confined water is lower than the bulk, due to the hydrophilic interaction between the water molecules and the hydroxylated silica surface. Our results also suggest that the self-diffusivity of confined water is sensitive to the adsorbed amount.
153 citations
TL;DR: The pea model can be used for characterization purposes where one is interested in capturing the global experimental behavior upon adsorption and desorption in silica nanopores and the bean model is more suitable to investigating the details of the interaction with the surface because this model, which accounts for the partial charges located on the nitrogen atoms of the molecule, allows a description of the specific interactions between this adsorbate and silica surfaces.
Abstract: This article reports on a molecular simulation study of nitrogen adsorption and condensation at 77 K in atomistic silica cylindrical nanopores (MCM-41). Two models are considered for the nitrogen m...
62 citations
TL;DR: The presence of hysteresis loops observed in adsorption isotherms measured in straight nanopores with closed bottom ends can be explained in terms of geometrical inhomogeneities along the pore axis.
Abstract: Capillary condensation in nanoporous anodic aluminum oxide presenting not interconnected pores with controlled modulations is studied using adsorption experiments and molecular simulations. Both the experimental and simulation data show that capillary condensation and evaporation are driven by the smallest size of the nanopore (constriction). The adsorption isotherms for the open and closed pores are almost identical if constrictions are added to the system. The latter result implies that the type of pore ending does not matter in modulated pores. Thus, the presence of hysteresis loops observed in adsorption isotherms measured in straight nanopores with closed bottom ends can be explained in terms of geometrical inhomogeneities along the pore axis. More generally, these results provide a general picture of capillary condensation and evaporation in constricted or modulated pores that can be used for the interpretation of adsorption in disordered porous materials.
54 citations
TL;DR: Chandler et al. as mentioned in this paper examined the effect of size and polarizability of the ions on the structure and dynamics of the confined electrolyte solution by considering the series of sodium halides (NaX with X = F, Cl, Br, and I).
Abstract: This paper reports on a molecular dynamics study of aqueous electrolyte solutions confined in hydrophobic nanopores. We examined for the first time the effect of the size and polarizability of the ions on the structure and dynamics of the confined electrolyte solution by considering the series of sodium halides (NaX with X = F, Cl, Br, and I). We also address the effect of pore size by varying the diameter of the nanochannel. As far as structural properties are concerned, the behavior of the NaF electrolyte solution significantly differs from that of the other sodium halide solutions. Because of their small size, Na and F in NaF are found to be significantly solvated by water. In addition, due to steric and hydrophobic effects [Chandler, D. Nature 2005, 437, 640.], Cl, Br, and I tend to be repelled from the regions where the density of water is larger. Ion-specific effects on the dynamics of water and ions are found to be minimized when the electrolyte solution is confined at the nanoscale in comparison t...
39 citations
TL;DR: No sharp change in the properties of the confined mixture occurs upon melting, which suggests that the confined system does not crystallize, and the composition of the mixture is shifted, upon confinement, toward the component having the strongest wall/fluid attraction.
Abstract: Freezing of mixtures confined in silica nanopores is investigated by means of experiment and molecular simulation. The experiments consist of differential scanning calorimetry and dielectric relaxation spectroscopy measurements for CCl(4)/C(6)H(5)Br mixtures confined in Vycor having pores with a mean diameter of about D=4.2 nm. Molecular simulations consist of grand canonical Monte Carlo simulations combined with the parallel tempering technique for Lennard-Jones Ar/Kr mixtures confined in a silica cylindrical nanopore with a diameter of D=3.2 nm. The experimental and molecular simulation data provide a consistent picture of freezing of mixtures in cylindrical silica nanopores having a size smaller than ten times the size of the confined molecules. No sharp change in the properties of the confined mixture occurs upon melting, which suggests that the confined system does not crystallize. In the case of the molecular simulations, this result is confirmed by the fact that except for the contact layer, the percentage of crystal-like atoms is less than 6% (whatever the temperature). The molecular simulations also show that the composition of the mixture is shifted, upon confinement, toward the component having the strongest wall/fluid attraction.
30 citations
TL;DR: In this paper, a molecular simulation study of ZnO nanostructures confined within carbon nanotubes is presented, where the effects of confinement (by varying the pore size and degree of pore filling) on the structure of the nanomaterial are addressed.
Abstract: This paper reports on a molecular simulation study of ZnO nanostructures confined within carbon nanotubes. Both the effects of confinement (by varying the pore size) and degree of pore filling (by varying the number of confined ZnO monomers) on the structure of the nanomaterial are addressed. None of the nanostructures exhibits the ideal structure of one of the ZnO bulk crystal phases (rocksalt, blende and wurtzite), but some crystalline features with significant correlations for the first and second nearest neighbours are observed. Close inspection of the location of the peaks in the pair correlation functions, of the angle distributions between Zn–O nearest neighbours and of some corresponding molecular configurations suggest that the confined nanoparticles possess mainly the local ordering of wurtzite. We also found evidence for defects such as Zn atoms that are involved in both a four-atom ring (characteristic of a cubic phase) and a six-atom ring (characteristic of wurtzite). Due to the smaller coord...
5 citations
TL;DR: An experimental and simulation study of binary mixtures of o- and m-nitrotoluene with decane and hexadecane, aimed at analysing the kind of phase transitions observed, and the conditions of their occurrence in a nonpolar/dipolar mixture.
Abstract: We report an experimental and simulation study of binary mixtures of o- and m-nitrotoluene with decane and hexadecane. Mixtures of o-nitrotoluene with alkanes form a classical critical mixtures, but m-nitrotoluene / n - alkane mixtures show an apparent critical point, which lies in a metastable, experimentally inaccessible state, below the melting point, affecting physical and chemical properties of this systems in the stable liquid phase. The presence of the apparent critical point in this mixture has been experimentally observed by Nonlinear Dielectric Effect (NDE) measurements as an anomalous increase in the NDE values typical of critical concentrations. The phase diagram of this mixture shows evidence that the system freezes in the homogenous phase and its melting point is higher than its critical temperature [1-3]. For such a system, we performed Monte Carlo simulations aimed at analysing the kind of phase transitions observed, and the conditions of their occurrence in a nonpolar/dipolar mixture. We perform studies for classical critical systems of o-nitrotoluene with decane and hexadecane The enthalpy, configurational energy and radial distribution function have been estimated by the MC simulation method in the NPT system. Immiscibility conditions according to Schoen and Hoheisel [4] approach are also discussed.
1 citations
TL;DR: In this article, various experimental and molecular simulation methods are used to investigate water adsorption and its related effects on ion dynamics in two typical examples of microporous solids: Na + -faujasites and homoionic alkali exchanged montmorillonites.
Abstract: Various experimental and molecular simulation methods are used to investigate water adsorption and its related effects on ion dynamics in two typical examples of microporous solids: Na + -faujasites and homoionic alkali exchanged montmorillonites. Influence of the confinement, of the cationic density and of the cation size is examined. It is then shown that all these parameters play a key role in water adsorption thermodynamics and in the cation/water subsystem dynamics.