Shape-controlled orientation and assembly of colloids with sharp edges in nematic liquid crystals

TL;DR

This study demonstrates how the shape and sharp edges of colloids influence defect configurations and assembly in nematic liquid crystals, enabling shape-based control of colloidal orientation and self-assembly.

Contribution

It reveals the impact of colloid shape, especially sharp edges, on defect pinning and orientation in nematic liquid crystals through numerical modeling and experiments.

Findings

Defects pin at sharp edges of colloids.

Colloids orient at shape-dependent oblique angles.

Shape tuning can control self-assembly outcomes.

Abstract

The assembly of colloids in nematic liquid crystals via topological defects has been extensively studied for spherical particles, and investigations of other colloid shapes have revealed a wide array of new assembly behaviors. We show, using Landau-de Gennes numerical modeling, that nematic defect configurations and colloidal assembly can be strongly influenced by fine details of colloid shape, in particular the presence of sharp edges. For cylinder, microbullet, and cube colloid geometries, we obtain the particles' equilibrium alignment directions and effective pair interaction potentials as a function of simple shape parameters. We find that defects pin at sharp edges, and that the colloid consequently orients at an oblique angle relative to the far-field nematic director that depends on the colloid's shape. This shape-dependent alignment, which we confirm in experimental measurements, raises the possibility of selecting self-assembly outcomes for colloids in liquid crystals by tuning particle geometry.