Evidence for the weak steric hindrance scenario in the supercooled-state reorientational dynamics

TL;DR

This study uses molecular dynamics simulations to explore how molecular shape influences rotational dynamics in supercooled liquids, revealing a weak steric hindrance scenario for small elongations consistent with mode-coupling theory.

Contribution

It demonstrates the existence of a weak steric hindrance scenario in supercooled liquids for small molecular elongations, supported by simulation results aligned with theoretical predictions.

Findings

Strong steric hindrance for elongated molecules

Weak steric hindrance scenario for small elongations

Agreement with mode-coupling theory predictions

Abstract

We use molecular-dynamics computer simulations to study the translational and reorientational dynamics of a glass-forming liquid of dumbbells. For sufficiently elongated molecules the standard strong steric hindrance scenario for the rotational dynamics is found. However, for small elongations we find a different scenario -- the weak steric hindrance scenario -- caused by a new type of glass transition in which the orientational dynamics of the molecule's axis undergoes a dynamical transition with a continuous increase of the non-ergodicity parameter. These results are in agreement with the theoretical predictions by the mode-coupling theory for the glass transition.