Heterogeneous Dynamics in Columnar Liquid Crystals of Parallel Hard Rods

TL;DR

This study uses computer simulations to explore the heterogeneous, hopping-type diffusion in columnar liquid crystal phases of aligned hard rods, revealing glass-like relaxation behaviors and non-Gaussian diffusion patterns.

Contribution

It is the first to analyze heterogeneous dynamics in columnar liquid crystal phases of parallel hard rods, highlighting free-energy barriers and glass-like relaxation phenomena.

Findings

Hopping-type diffusion caused by free-energy barriers

Two-step structural relaxation similar to glass-formers

Non-Gaussian inter-column diffusion observed

Abstract

In the wake of previous studies on the rattling-and-jumping diffusion in smectic liquid crystal phases of colloidal rods, we analyze here for the first time the heterogeneous dynamics in columnar phases. More specifically, we perform computer simulations to investigate the relaxation dynamics of a binary mixture of perfectly aligned hard spherocylinders. We detect that the columnar arrangement of the system produces free-energy barriers the particles should overcome to jump from one column to another, thus determining a hopping-type diffusion. This phenomenon accounts for the non-Gaussian inter-column diffusion and shows a two-step structural relaxation which is remarkably analogous to that of out-of-equilibrium glass-forming systems and gels. Surprisingly enough, slight deviations from the behavior of simple liquids due to transient cages is also observed in the direction perpendicular to this plane, where the system is usually referred to as liquid-like.