Switching dynamics in cholesteric liquid crystal emulsions

TL;DR

This study numerically investigates how cholesteric liquid crystal droplets respond dynamically to various electric fields, revealing complex defect behaviors and potential for novel device applications.

Contribution

It provides a detailed numerical analysis of the switching dynamics of cholesteric droplets under different electric field conditions, highlighting the effects of anchoring and field orientation.

Findings

Metastable states with topological defects form under uniform fields parallel to the cholesteric axis.

Tangential anchoring results in fewer defects at equilibrium.

Rotating electric fields induce defect and droplet rotation at lower speeds.

Abstract

In this work we numerically study the switching dynamics of a 2D cholesteric emulsion droplet immersed in an isotropic fluid under an electric field, which is either uniform or rotating with constant speed. The overall dynamics depend strongly on the magnitude and on the direction (with respect to the cholesteric axis) of the applied field, on the anchoring of the director at the droplet surface and on the elasticity. If the surface anchoring is homeotropic and a uniform field is parallel to the cholesteric axis, the director undergoes deep elastic deformations and the droplet typically gets stuck into metastable states which are rich in topological defects. When the surface anchoring is tangential, the effects due to the electric field are overall less dramatic, as a small number of topological defects form at equilibrium. The application of the field perpendicular to the cholesteric axis usually has negligible effects on the defect dynamics. The presence of a rotating electric field of varying frequency fosters the rotation of the defects and of the droplet as well, typically at lower speed than that of the field, due to the inertia of the liquid crystal. If the surface anchoring is homeotropic a periodic motion is found. Our results represent a first step to understand the dynamical response of a cholesteric droplet under an electric field and its possible application in designing novel liquid crystal-based devices.