Demixing and confinement in slit pores

TL;DR

This study uses Monte Carlo simulations to explore how geometric confinement in slit pores affects the demixing behavior of symmetric non-additive hard sphere mixtures, revealing complex dependencies on pore size and non-additivity.

Contribution

It provides new insights into the effects of confinement on phase separation in non-additive hard sphere mixtures, including conditions where confinement induces demixing.

Findings

Confinement generally impedes phase separation due to volume effects.

Critical pressure and density vary non-monotonically with pore size for small non-additivities.

Confinement can induce demixing in otherwise stable mixtures when pore width is very small.

Abstract

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. We find that for this particular case in which demixing is induced by volume effects, phase separation is in most cases somewhat impeded by spatial confinement. 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 forced to demix by simple geometric confinement when the pore width decreases down to approximately one and a half molecular diameters.