Electro-Mechanical Fredericks Effects in Nematic Gels

TL;DR

This paper investigates the electro-mechanical Fredericks effects in nematic gels, revealing a critical field dependence and the influence of director elasticity and initial misorientation on optical anisotropy.

Contribution

It introduces the concept of a critical field in nematic gels and models the director response considering both quartic and harmonic elasticity effects.

Findings

Critical field dependence differs from classical case

Director response influenced by competition between elasticities

Model aligns with experimental optical anisotropy measurements

Abstract

The solid nematic equivalent of the Fredericks transition is found to depend on a critical field rather than a critical voltage as in the classical case. This arises because director anchoring is principally to the solid rubbery matrix of the nematic gel rather than to the sample surfaces. Moreover, above the threshold field, we find a competition between quartic (soft) and conventional harmonic elasticity which dictates the director response. By including a small degree of initial director misorientation, the calculated field variation of optical anisotropy agrees well with the conoscopy measurements of Chang et al (Phys.Rev.E56, 595, 1997) of the electro-optical response of nematic gels.