Anisotropic translational diffusion in the nematic phase: Dynamical signature of the coupling between orientational and translational order in the energy landscape

TL;DR

This study investigates how the translational diffusion coefficient in nematic liquid crystals varies with temperature, revealing a non-monotonic behavior linked to the coupling between orientational and translational order, analyzed through an energy landscape approach.

Contribution

It introduces an energy landscape framework to explain the non-monotonic temperature dependence of anisotropic translational diffusion in nematic liquid crystals.

Findings

D_parallel increases then decreases with temperature in the nematic phase.

The reversal correlates with the emergence of smectic order in the energy landscape.

Coupling between orientational and translational order influences diffusion behavior.

Abstract

We find in a model system of thermotropic liquid crystals that the translational diffusion coefficient parallel to the director $D_{\parallel}$ first increases and then decreases as temperature drops through the nematic phase, and this reversal occurs where the smectic order parameter of the underlying inherent structures becomes significant for the first time. We argue, based on an energy landscape analysis, that the coupling between orientational and translational order can play a role in inducing the non-monotonic temperature behavior of $D_{\parallel}$. Such a view is likely to form the foundation of a theoretical framework to explain the anisotropic translation diffusion.