Maier-Saupe-type theory of ferroelectric nanoparticles in nematic liquid crystals

TL;DR

This paper develops a Maier-Saupe-type theoretical model to accurately describe the effects of ferroelectric nanoparticles on nematic liquid crystals, especially capturing low-temperature saturation of order parameters, improving upon previous Landau theory models.

Contribution

The paper introduces a new Maier-Saupe-type model that explicitly accounts for low-temperature saturation of order parameters, extending previous Landau theory approaches.

Findings

The model aligns well with experimental data on ferroelectric nanoparticles in liquid crystals.

It predicts different behavior at low temperatures compared to Landau theory.

The model reduces to Landau theory in high-temperature or weak-coupling limits.

Abstract

Several experiments have reported that ferroelectric nanoparticles have drastic effects on nematic liquid crystals--increasing the isotropic-nematic transition temperature by about 5 K, and greatly increasing the sensitivity to applied electric fields. In a recent paper [L. M. Lopatina and J. V. Selinger, Phys. Rev. Lett. 102, 197802 (2009)], we modeled these effects through a Landau theory, based on coupled orientational order parameters for the liquid crystal and the nanoparticles. This model has one important limitation: Like all Landau theories, it involves an expansion of the free energy in powers of the order parameters, and hence it overestimates the order parameters that occur in the low-temperature phase. For that reason, we now develop a new Maier-Saupe-type model, which explicitly shows the low-temperature saturation of the order parameters. This model reduces to the Landau theory in the limit of high temperature or weak coupling, but shows different behavior in the opposite limit. We compare these calculations with experimental results on ferroelectric nanoparticles in liquid crystals.