Using Monte Carlo simulation, we study the influence of geometric confinement on demixing for a series of symmetric non-additive hard spheres mixtures confined in slit pores. We consider both a wide range of positive non-additivities and a series of pore widths, ranging from the pure two dimensional limit to a large pore width where results are close to the bulk three dimensional case. Critical parameters are extracted by means of finite size analysis. As a general trend, we find that for this particular case in which demixing is induced by volume effects, the critical demixing densities (and pressures) increase due to confinement between neutral walls, following the expected behavior for phase equilibria of systems confined by pure repulsive walls: i.e., confinement generally enhances miscibility. However, a non-monotonous dependence of the critical pressure and density with pore size is found for small non-additivities. In this latter case, it turns out that an otherwise stable bulk mixture can be unexpectedly forced to demix by simple geometric confinement when the pore width decreases down to approximately one and a half molecular diameters. C 2015 AIP Publishing LLC. [http://dx

We study the fluid inclusion of both Lennard-Jones particles and particles with competing interaction ranges -short range attractive and long range repulsive (SALR)-in a disordered porous medium constructed as a controlled pore glass in two dimensions. With the aid of a full twodimensional Ornstein-Zernike approach, complemented by a Replica Ornstein-Zernike integral equation, we explicitly obtain the spatial density distribution of the fluid adsorbed in the porous matrix and a good approximation for the average fluid-matrix correlations. The results illustrate the remarkable differences between the adsorbed Lennard-Jones (LJ) and SALR systems. In the latter instance, particles tend to aggregate in clusters which occupy pockets and bays in the porous structure, whereas the LJ fluid uniformly wets the porous walls. A comparison with Molecular Dynamics simulations shows that the two-dimensional Ornstein-Zernike approach with a Hypernetted Chain closure together with a sensible approximation for the fluid-fluid correlations can provide an accurate picture of the spatial distribution of adsorbed fluids for a given configuration of porous material.

In this work, we explore the ability of an inhomogeneous integral equation approach to provide a full three dimensional description of simple fluids under conditions of confinement in porous media. Explicitly, we will consider the case of argon adsorbed into silicalite-1, silicalite-2, and an all-silica analogue of faujasite, with a porous structure composed of linear (and zig-zag in the case of silicalite-1) channels of 5-8 Å diameter. The equation is based on the three dimensional Ornstein-Zernike approximation proposed by Beglov and Roux [J. Chem. Phys. 103, 360 (1995)] in combination with the use of an approximate fluid-fluid direct correlation function furnished by the replica Ornstein-Zernike equation with a hypernetted chain closure. Comparison with the results of grand canonical Monte Carlo/molecular dynamics simulations evidences that the theory provides an accurate description for the three dimensional density distribution of the adsorbed fluid, both at the level of density profiles and bidimensional density maps across representative sections of the porous material. In the case of very tight confinement (silicalite-1 and silicalite-2), solutions at low temperatures could not be found due to convergence difficulties, but for faujasite, which presents substantially larger channels, temperatures as low as 77 K are accessible to the integral equation. The overall results indicate that the theoretical approximation can be an excellent tool to characterize the microscopic adsorption behavior of porous materials. C 2015 AIP Publishing LLC. [http://dx

The stability of complexes of a recently synthetized (Scott et al. J. Am. Chem. Soc.2011, 134, 107) opened nanocontainer C50H10 with several guest molecules, H2, N2, CO, HCN, H2O, CO2, CS2, H2S, C2H2, NH3, CH4, CH3CN, CH3OH, CH3CCH, 2-butyne, methyl halides, and with noble gas atoms, has been examined by means of symmetry-adapted perturbation theory of intermolecular interactions, which fully incorporates all important energy components, including a difficult dispersion term. All complexes under scrutiny have been found stable for all studied guests at 0 K, but entropic effects cause many of them to dissociate into constituent molecules under standard conditions. The estimation of temperature at which the Gibbs free energy ΔG = 0 revealed that the recently observed (Scott et al. J. Am. Chem. Soc.2011, 134, 107) complex CS2@C50H10 is the most stable at room temperature while the corresponding complexes with HCN and Xe guests should decompose at ca. 310 K and that with CO2 at room temperature (ca. 300 K). In agreement with the ΔG estimation, molecular dynamics simulations performed in vacuum for the CS2@C50H10 complex predicted that the complex is stable but decomposes at ca. 350 K. The MD simulations in CHCl3 solution showed that the presence of solvent stabilizes the CS2@C50H10 complex in comparison to vacuum. Thus, for the complexes obtained in solution the CO2 gas responsible for the greenhouse effect could be stored in the C50H10 nanotube.

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