Computer simulation of topological defects around a colloidal particle or droplet dispersed in a nematic host

TL;DR

This study uses molecular dynamics simulations to explore the formation and structure of topological defects around spherical particles in nematic liquid crystals, revealing different defect configurations and their dependence on particle size.

Contribution

It provides detailed simulation-based insights into defect structures around colloidal particles in nematics, extending understanding beyond elastic theory predictions.

Findings

Identified three defect structures: quadrupolar, dipolar, and transitional ring defects.

Observed defect positions vary with particle size, aligning with elastic theory.

Analyzed defect core regions where elastic theory does not apply.

Abstract

We use molecular dynamics to study the ordering of a nematic liquid crystal around a spherical particle or droplet. Homeotropic boundary conditions and strong anchoring create a hedgehog director configuration on the particle surface and in its vicinity; this topological defect is cancelled by nearby defect structures in the surrounding liquid crystal, so as to give a uniform director field at large distances. We observe three defect structures for different particle sizes: a quadrupolar one with a ring defect surrounding the particle in the equatorial plane; a dipolar one with a satellite defect at the north or south pole; and a transitional, non-equatorial, ring defect. These observations are broadly consistent with the predictions of the simplest elastic theory. By studying density and order-parameter maps, we are able to examine behaviour near the particle surface, and in the disclination core region, where the elastic theory is inapplicable. Despite the relatively small scale of the inhomogeneities in our systems, the simple theory gives reasonably accurate predictions of the variation of defect position with particle size.