Three-dimensional modeling of chiral nematic texture evolution under electric switching

TL;DR

This paper presents the first 3D finite difference modeling of electric field-induced texture transitions in chiral nematic liquid crystals, revealing defect morphologies and dynamic recovery behaviors relevant for device design.

Contribution

It introduces a novel 3D modeling approach for chiral nematic textures under electric switching, including defect dynamics and elastic constant variations.

Findings

Fast recovery of planar state without transient planar phase

Diverse defect-rich morphologies in focal conic textures

Effective modeling of elastic constant effects on transitions

Abstract

Chiral nematic liquid crystals exhibit both a helical planar ground state with uniform twist and a metastable defect-rich focal conic texture, and can be switched between the two microstructures via application of transient voltage pulses. In this work, we model these electrically-induced texture transitions using finite difference methods to examine resulting microstructural evolution, the first time this transition has been modeled in three dimensions. We analyze the planar to focal conic, focal conic to planar, and planar to planar transitions depending on voltage pulse magnitude. We consider first the special case of chiral nematics with matched twist and bend elastic constants. Results show a variety of defect-rich morphologies in the disordered focal conic texture and demonstrate a fast recovery of the planar ground state on switching without formation of a transient planar state. We evaluate both texture microstructural evolution as well as cell capacitance. Beyond the single elastic constant approximation, we evaluate the planar to transient-planar as well as the planar to Helfrich-deformed transitions in simulations of a liquid crystal compound with different elastic constants. Our methods represent the evolving microstructure as a uniaxial director field, with relaxation dynamics calculated from a tensor representation so that half charge disclination defects are not suppressed. We discuss potential application of these computationally efficient three-dimensional modeling approaches for design and optimization of chiral nematic devices.