Anisotropic wave propagation in nematic liquid crystals

TL;DR

This paper explains anisotropic wave propagation in nematic liquid crystals using a first-gradient continuum theory, addressing longstanding experimental observations of sound velocity anisotropy and frequency dependence.

Contribution

It introduces a novel continuum model based on hyperelastic anisotropic response to explain acoustic features in nematic liquid crystals.

Findings

The model reproduces observed anisotropic sound velocity.

It accounts for frequency dependence of wave propagation.

Comparison with second-gradient fluid model highlights advantages.

Abstract

Despite the fact that quantitative experimental data have been available for more than forty years now, nematoacoustics still poses intriguing theoretical and experimental problems. In this paper, we prove that the main observed features of acoustic wave propagation through a nematic liquid crystal cell -- namely, the anisotropy of sound velocity and its frequency dependence -- may be plausibly explained by a first-gradient continuum theory characterized by a hyperelastic anisotropic response from an evolving relaxed configuration. We compare and contrast our proposal with a competing theory where the liquid crystal is modeled as an isotropically compressible, anisotropic second-gradient fluid.