Non-linear dielectric effect in the isotropic phase above the isotropic-cholesteric phase transition

TL;DR

This paper models the non-linear dielectric effect in the isotropic phase near the isotropic-cholesteric transition using Landau-de Gennes theory, accounting for temperature, pressure, and frequency dependencies and explaining experimental pretransitional phenomena.

Contribution

It introduces a theoretical model that captures the complex pretransitional dielectric effects in polar cholesterics, aligning well with experimental observations.

Findings

Model explains negative and positive pretransitional effects

Pressure influences the isotropic-cholesteric transition

Results qualitatively match experimental data

Abstract

Using the Landau-de Gennes theory, the temperature, pressure and frequency dependence of the non-linear effect in the isotropic phase above the isotropic-cholesteric phase transition is calculated. The influence of pressure on the isotropic-cholesteric phase transition is discussed by varying the coupling between the orientational order parameter and the macroscopic polarization of polar cholesterics. Comparing the results of the calculations with existing data, we finally conclude that the model provides a description of the isotropic-cholesteric transition that takes all experimentally known features of the unusual negative and positive pretransitional effect in the isotropic phase of the system into account in a qualitatively correct way.