Wetting and capillary nematization of binary hard-platelet and hard-rod fluids

TL;DR

This study uses density-functional theory to analyze the phase behavior and wetting phenomena of binary hard-platelet and hard-rod fluids near surfaces and in confined geometries, revealing surface transitions and capillary nematization.

Contribution

It introduces a numerical analysis of the Zwanzig model for binary platelet and rod fluids, uncovering surface and confinement-induced phase transitions.

Findings

Wall-induced uniaxial to biaxial transition for rods

Complete wetting of the wall by biaxial nematic film for rods

First-order capillary nematization transition with a critical point

Abstract

Density-functional theory is used to investigate the phase behavior of colloidal binary hard-platelet and hard-rod fluids near a single hard wall or confined in a slit pore. The Zwanzig model, in which the orientations of the particles of rectangular shape are restricted to three orthogonal orientations, is analyzed by numerical minimization of the grand potential functional. The density and orientational profiles as well as the surface contributions to the grand potential are determined. The calculations exhibit a wall-induced continuous surface transition from uniaxial to biaxial symmetry for the hard-rod fluid. Complete wetting of the wall -- isotropic liquid interface by a biaxial nematic film for rods and a uniaxial nematic film for platelets is found. For the fluids confined by two parallel hard walls we determine a first-order capillary nematization transition for large slit widths, which terminates in a capillary critical point upon decreasing the slit width.