Ring around the colloid

TL;DR

This paper investigates the defect structures formed by Janus washers in nematic liquid crystals, revealing a unique topological defect loop and novel colloidal arrangements influenced by anchoring conditions.

Contribution

It introduces the discovery of topologically required defect loops in Janus washers and demonstrates how their tilting behavior can be controlled by additional colloids.

Findings

Janus washers form a disclination loop defect in nematic liquid crystals.

The defect structure causes the colloid-defect pair to tilt relative to the far field director.

Adding a spherical colloid inside the washer suppresses tilting, enabling new colloidal assemblies.

Abstract

In this work, we show that Janus washers, genus-one colloids with hybrid anchoring conditions, form topologically required defects in nematic liquid crystals. Experiments under crossed polarizers reveal the defect structure to be a rigid disclination loop confined within the colloid, with an accompanying defect in the liquid crystal. When confined to a homeotropic cell, the resulting colloid-defect ring pair tilts relative to the far field director, in contrast to the behavior of toroidal colloids with purely homeotropic anchoring. We show that this tilting behavior can be reversibly suppressed by the introduction of a spherical colloid into the center of the toroid, creating a new kind of multi-shape colloidal assemblage.