Glassy orientational dynamics of rodlike molecules near the isotropic-nematic transition

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 nonexponential 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 established 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 observed for glass-forming liquids. A plausible correlation between the energy landscape features and the observed fragility is discussed.