Bulk fluid phase behaviour of colloidal platelet-sphere and platelet-polymer mixtures

TL;DR

This study uses a density functional theory to analyze the phase behavior of colloidal mixtures of platelets, spheres, and polymers, revealing various phase separations and demixing phenomena depending on particle size ratios.

Contribution

It introduces a fundamental-measure density functional for platelet-sphere and platelet-polymer mixtures, predicting complex phase diagrams and demixing behaviors.

Findings

Isotropic-nematic phase separation broadens with pressure.

Large size ratio mixtures show nematic-nematic demixing.

Platelet-polymer mixtures exhibit isotropic-isotropic demixing at low size ratios.

Abstract

Using a geometry-based fundamental measure density functional theory, we calculate bulk fluid phase diagrams of colloidal mixtures of vanishingly thin hard circular platelets and hard spheres. We find isotropic-nematic phase separation with strong broadening of the biphasic region upon increasing the pressure. In mixtures with large size ratio of platelet and sphere diameter, there is also demixing between two nematic phases with differing platelet concentrations. We formulate a fundamental-measure density functional for mixtures of colloidal platelets and freely overlapping spheres, which represent ideal polymers, and use it to obtain phase diagrams. We find that for low platelet-polymer size ratio in addition to isotropic-nematic and nematic-nematic phase coexistence, platelet-polymer mixtures also display isotropic-isotropic demixing. In contrast, we do not find isotropic-isotropic demixing in hard core platelet-sphere mixtures for the size ratios considered.