A hard sphere fluid in equilibrium with microporous membranes. Inhomogeneous replica Ornstein—Zernike equations and grand canonical Monte Carlo simulations

Fluids in porous media. IV. Quench effect on chemical potential

It appears to be a common sense to measure the crowdedness of a fluid system by the densities of the species constituting it. In the present work, we show that this ceases to be valid for confined fluids under some conditions. A quite thorough investigation is made for a hard sphere (HS) fluid adsorbed in a hard sphere matrix (a quench-annealed system) and its corresponding equilibrium binary mixture. When fluid particles are larger than matrix particles, the quench-annealed system can appear much more crowded than its corresponding equilibrium binary mixture, i.e., having a much higher fluid chemical potential, even when the density of each species is strictly the same in both systems, respectively. We believe that the insight gained from this study should be useful for the design of functionalized porous materials.

Capillary condensation in pores with rough walls: A density functional approach

The effect of surface roughness of slit-like pore walls on the capillary condensation of a spherical particles and short chains is studied. The gas molecules interact with the substrate by a Lennard-Jones (9,3) potential. The rough layer at each pore wall has a variable thickness and density and consists of a disordered quenched matrix of spherical particles. The system is described in the framework of a density functional approach and using computer simulations. The contribution due to attractive van der Waals interactions between adsorbate molecules is described by using first-order mean spherical approximation and mean-field approximation.

Computer simulations of phase equilibrium for a fluid confined in a disordered porous structure

We present calculations of the phase diagrams of a Lennard-Jones 12-6 fluid confined in a disordered porous structure made up of a dispersion of spherical particles, following up on an earlier work on the same system. In particular we present additional calculations using more realizations of the matrix and we investigate the applicability of the Gibbs-Duhem integration method to the calculation of phase equilibrium in these systems. The essential picture of disordered and inhomogeneous coexisting vapor and liquid phases, which emerged in the earlier work, is confirmed by the new calculations. However, a second phase transition associated with the wetting of the porous material by the fluid is found to be more sensitive to variations of the matrix realization. While for the present model this transition appears for particular realizations of the matrix, it does not seem to survive averaging over realizations.

Effective Interactions in a Quenched-Annealed Hard-Sphere Mixture Confined in a Narrow Slit-like Pore

We consider a slit-like pore filled with a disordered hard-sphere matrix. The diameter of matrix species is chosen almost equal to the pore width. Another hard-sphere fluid species, of smaller diameter, enters, at a given chemical potential, into this confined quenched microporous medium. The model is similar to the experimental setup; see G. Cruz de Leon et al. Phys. Rev. Lett. 81, 1122 (1998). The model is solved by using the inhomogeneous replica Ornstein-Zernike equations with Percus-Yevick approximation. We discuss the effective interactions between species in a confined medium on the chemical potential and matrix microporosity. Copyright 1999 Academic Press.