Lattice Boltzmann modeling of cholesteric liquid crystal droplets under an oscillatory electric field

TL;DR

This study uses lattice Boltzmann simulations to explore how cholesteric liquid crystal droplets respond to oscillatory electric fields, revealing complex rotational and defect dynamics influenced by field parameters.

Contribution

It introduces a hybrid numerical approach to model cholesteric droplets under oscillatory fields, highlighting the impact on defect motion and droplet behavior, which was not previously detailed.

Findings

Liquid crystal droplets rotate coherently under electric fields.

Topological defects exhibit chaotic or regular motion depending on cholesteric pitch.

Droplet and fluid angular velocities depend on field frequency and magnitude.

Abstract

We numerically study the dynamics of quasi-two dimensional cholesteric liquid crystal droplets in the presence of a time-dependent electric field, rotating at constant angular velocity. A surfactant sitting at droplet interface is also introduced to prevent droplet coalescence. The dynamics is modeled following a hybrid numerical approach, where a standard lattice Boltzmann technique solves the Navier-Stokes equation and a finite difference scheme integrates the evolution equations of liquid crystal and surfactant. Our results show that, once the field is turned on, the liquid crystal rotates coherently triggering a concurrent orbital motion of both droplets around each other, an effect due to the momentum transfer to the surrounding fluid. In addition the topological defects, resulting from the conflict orientation of the liquid crystal within the drops, exhibit a chaotic-like motion in cholesterics with a high pitch, in contrast with a regular one occurring along circular trajectories observed in nematics drops. Such behavior is found to depend on magnitude and frequency of the applied field as well as on the anchoring of the liquid crystal at the droplet interface. These findings are quantitatively evaluated by measuring the angular velocity of fluid and drops for various frequencies of the applied field.