Vapour-liquid phase behaviour of primitive models of ionic liquids confined in disordered porous media

TL;DR

This paper develops a theoretical framework to analyze the vapour-liquid phase behavior of ionic liquids confined in disordered porous media, accounting for ion shape and matrix effects.

Contribution

It introduces a combined theoretical approach to predict phase diagrams of ionic liquids in porous media, considering ion shape and confinement effects.

Findings

Matrix confinement influences phase stability.

Cation shape affects phase diagram topology.

The theory provides analytical expressions for thermodynamic properties.

Abstract

We develop a theory for the description of ionic liquids (ILs) confined in a porous medium formed by a matrix of immobile randomly placed uncharged particles. The IL is modelled as an electroneutral mixture of hardsphere anions and flexible linear chain cations, represented by tangentially bonded hard spheres with the charge located on one of the terminal beads. The theory combines a generalization of the scaled particle theory, Wertheim's thermodynamic perturbation theory, and the associative mean-spherical approximation and allows one to obtain analytical expressions for the pressure and chemical potentials of the matrix-IL system. Using the theory, we calculate the vapour-liquid phase diagrams for two versions of the IL model, i.e., when the cation is modelled as a dimer and as a chain, in a complete association limit. The effects of the matrix confinement and of the non-spherical shape of the cations on the vapour-liquid phase diagrams are studied.