Isotropic-Nematic Transition in Liquid-Crystalline Elastomers: Lattice Model with Quenched Disorder

TL;DR

This paper develops a lattice model to study how quenched disorder affects the isotropic-nematic transition in liquid-crystalline elastomers, showing that disorder broadens the transition into a smooth crossover, aligning with experimental observations.

Contribution

It introduces a lattice model incorporating disorder types and demonstrates how they influence the transition, providing insights into experimental phenomena.

Findings

Both disorder types cause the transition to broaden into a smooth crossover.

Random-field disorder's effect is mediated by long-range elastic interactions.

Model results are consistent with experimental observations.

Abstract

When liquid-crystalline elastomers pass through the isotropic-nematic transition, the orientational order parameter and the elastic strain vary rapidly but smoothly, without the expected first-order discontinuity. This broadening of the phase transition is an important issue for applications of liquid-crystalline elastomers as actuators or artificial muscles. To understand this behavior, we develop a lattice model of liquid-crystalline elastomers, with local directors coupled to a global strain variable. In this model, we can consider either random-bond disorder (representing chemical heterogeneity) or random-field disorder (representing heterogeneous local stresses). Monte Carlo simulations show that both types of disorder cause the first-order isotropic-nematic transition to broaden into a smooth crossover, consistent with the experiments. For random-field disorder, the smooth crossover into an ordered state can be attributed to the long-range elastic interaction.