Demixing can occur in binary hard-sphere mixtures with negative non-additivity

TL;DR

This study investigates demixing in high-dimensional binary hard-sphere mixtures with negative non-additivity, revealing conditions under which phase separation occurs even with slight negative non-additivity.

Contribution

It demonstrates that demixing can occur in high-dimensional non-additive hard-sphere mixtures with negative non-additivity, extending understanding of phase behavior in such systems.

Findings

Demixing transition exists at high dimensions for certain negative non-additivity values.

Critical packing fraction scales as  2^{-d} in the limit of infinite dimensions.

Demixing stability with respect to freezing is analyzed.

Abstract

A binary fluid mixture of non-additive hard spheres characterized by a size ratio $\gamma=\sigma_2/\sigma_1<1$ and a non-additivity parameter $\Delta=2\sigma_{12}/(\sigma_1+\sigma_2)-1$ is considered in infinitely many dimensions. From the equation of state in the second virial approximation (which is exact in the limit $d\to\infty$) a demixing transition with a critical consolute point at a packing fraction scaling as $\eta\sim d 2^{-d}$ is found, even for slightly negative non-additivity, if $\Delta>-{1/8}(\ln\gamma)^2$. Arguments concerning the stability of the demixing with respect to freezing are provided.