Colloidal hard-rod fluids near geometrically structured substrates

TL;DR

This study uses density functional theory to analyze how colloidal hard-rod fluids behave near structured surfaces, revealing enrichment and depletion effects, and detailing the wetting transition of nematic films on patterned walls.

Contribution

It provides a detailed numerical analysis of rod orientations and density profiles near complex geometries, including wedge, edge, and patterned walls, using the Zwanzig model.

Findings

Rod enrichment near wedge corners and depletion near edges.

Complete wetting of patterned walls by nematic films occurs in two stages.

Nematic film thickness diverges near isotropic-nematic coexistence.

Abstract

Density functional theory is used to study colloidal hard-rod fluids near an individual right-angled wedge or edge as well as near a hard wall which is periodically patterned with rectangular barriers. The Zwanzig model, in which the orientations of the rods are restricted to three orthogonal orientations but their positions can vary continuously, is analyzed by numerical minimization of the grand potential. Density and orientational order profiles, excess adsorptions, as well as surface and line tensions are determined. The calculations exhibit an enrichment [depletion] of rods lying parallel and close to the corner of the wedge [edge]. For the fluid near the geometrically patterned wall, complete wetting of the wall -- isotropic liquid interface by a nematic film occurs as a two-stage process in which first the nematic phase fills the space between the barriers until an almost planar isotropic -- nematic liquid interface has formed separating the higher-density nematic fluid in the space between the barriers from the lower-density isotropic bulk fluid. In the second stage a nematic film of diverging film thickness develops upon approaching bulk isotropic -- nematic coexistence.