Phase coexistence and interface structure of a two-component Lennard-Jones fluid in porous media: application of Born—Green—Yvon equation

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.

Phase diagrams for multi-component membrane vesicles: a coarse-grained modeling study

We develop a multicomponent membrane coarse-grained model in which the effects of spontaneous curvature and fluidity are included. This model is used to perform computer simulations to study the phase segregation, domain coarsening, budding and budding off of multicomponent membrane vesicles. Three types of phase diagram are presented with variation of composition, spontaneous curvature, and line tension (the unlike bond energy). Various phases have been observed, including, sphere, biconcave, starfish, capsule, budding, and budding off. Our simulations show that budding off occurs only when the size of a domain is larger than a critical value, and the critical condition is closely related to the spontaneous curvature and line tension. A continuum model is used to predict the critical condition for budding off. Quantitative comparisons are made between the present simulation results and the continuum model predictions, and good agreements have been achieved.

Phase behavior of a binary symmetric mixture in slitlike pores with opposing walls: application of density functional approach

We study adsorption of a symmetric binary Lennard-Jones mixture, which exhibits partial mixing in a bulk phase, in slitlike pores formed by the walls having antisymmetric properties with respect to the components. The calculations are carried out by means of a density functional approach. We show that under suitable conditions the pore filling may occur as a sequence of two first-order transitions. The capillary condensation may lead to an "antisymmetric" liquidlike film, the symmetry of which follows the symmetry of the adsorbing potential, or to a "demixed" film, the symmetry of which is only weakly associated with the symmetry of the adsorption potential. The additional first-order antisymmetric-demixed film transition begins at the triple point temperature and ends at the critical end point temperature.

Capillary condensation and interface structure of a model colloid-polymer mixture in a porous medium

We consider the Asakura-Oosawa model of hard sphere colloids and ideal polymers in contact with a porous matrix modeled by immobilized configurations of hard spheres. For this ternary mixture a fundamental measure density functional theory is employed, where the matrix particles are quenched and the colloids and polymers are annealed, i.e., allowed to equilibrate. We study capillary condensation of the mixture in a small sample of matrix as well as demixing and the fluid-fluid interface inside a bulk matrix. Density profiles normal to the interface and surface tensions are calculated and compared to the case without matrix. Two kinds of matrices are considered: (i) colloid-sized matrix particles at low packing fractions and (ii) large matrix particles at high packing fractions. These two cases show fundamentally different behavior and should both be experimentally realizable. Furthermore, we argue that capillary condensation of a colloidal suspension could be experimentally accessible. We find that in case (ii), even at high packing fractions, the main effect of the matrix is to exclude volume and, to high accuracy, the results can be mapped onto those of the same system without matrix via a simple rescaling.