How glassy are orientational dynamics of rodlike molecules near the isotropic-nematic transition?

TL;DR

This study investigates the glassy-like slow dynamics of rodlike molecules near the isotropic-nematic transition in liquid crystals, revealing non-exponential relaxation, heterogeneity, and a fragility index similar to glass-forming liquids.

Contribution

It introduces a quantitative measure of glassy dynamics in liquid crystals by defining a fragility index based on relaxation times, linking it to energy landscape features.

Findings

Observation of non-exponential relaxation and heterogeneity.

Identification of a fragility index comparable to glass-forming liquids.

Correlation between energy landscape and fragility discussed.

Abstract

In an attempt to quantitatively characterize the recently observed slow dynamics in the isotropic and nematic phase of liquid crystals, we investigate the single-particle orientational dynamics of rodlike molecules across the isotropic-nematic transition in computer simulations of a family of model systems of thermotropic liquid crystals. Several remarkable features of glassy dynamics are on display including non-exponential relaxation, dynamical heterogeneity, and non-Arrhenius temperature dependence of the orientational relaxation time. In order to obtain a quantitative measure of glassy dynamics in line with the estbalished methods in supercooled liquids, we construct a relaxation time versus scaled inverse temperature plot, and demonstrate that one can indeed define a 'fragility index' for thermotropic liquid crystals, that depends on density and aspect ratio. The values of the fragility parameter are surprisingly in the range one observed for glass forming liquids. A plausible correlation between the energy landscape features and the observed fragility is discussed.