Tracking three-phase coexistences in binary mixtures of hard plates and spheres

TL;DR

This study uses Parsons-Lee theory to analyze phase coexistences in binary mixtures of hard plates and spheres, revealing conditions for demixing and the limitations of excluded volume interactions in explaining experimental observations.

Contribution

It provides new insights into the stability of different phase demixing in mixtures of hard plates and spheres, highlighting the role of size ratios and aspect ratios.

Findings

Isotropic-isotropic demixing likely preempted by crystallization.

Nematic-nematic demixing stabilized at low size and aspect ratios.

Excluded volume interactions explain nematic-nematic but not isotropic-isotropic demixing.

Abstract

The stability of demixing phase transition in binary mixtures of hard plates (with thickness L and diameter D) and hard spheres (with diameter $\sigma$) is studied by means of Parsons-Lee theory. The isotropic-isotropic demixing, which is found in mixtures of large spheres and small plates, is very likely to be preempted by crystallization. In contrast, the nematic-nematic demixing, which is obtained in mixtures of large plates and small spheres, can be stabilized at low diameter ratios ($\sigma$/D) and aspect ratios (L/D). At intermediate values of $\sigma$/D, where the sizes of the components are similar, neither the isotropic-isotropic nor the nematic-nematic demixing can be stabilized, but a very strong fractionation takes place between a plate rich nematic and a sphere rich isotropic phases. Our results show that the excluded volume interactions are capable alone to explain the experimental observation of the nematic-nematic demixing, but they fail for the description of isotropic-isotropic one (Chen et. al., Soft Matter, 11, 5775 (2015)).