Effects of disordered porous media on the vapour-liquid phase equilibrium in ionic fluids: application of the association concept

Abstract

Abstract We study the vapour-liquid phase diagram of a model ionic fluid, the so-called restricted primitive model, confined in a disordered porous medium formed by the matrix of hard sphere (HS) or overlapping hard sphere (OHS) particles. Our theoretical approach is based on a combination of the scaled-particle theory and the associative mean-spherical approximation incorporating the concept of ion association. It is shown that the HS and OHS matrices have a similar effect on the phase diagrams of an ionic fluid: the critical temperature T c and the critical density ρ c lower with a decrease of the matrix porosity and the coexistence region gets narrower. However, quantitatively both T c and ρ c are higher in the case of OHS matrix than in the HS matrix. It is also observed that the presence of disordered porous media leads to a decrease of the degree of dissociation in comparison with the bulk case.