Roles of icosahedral and crystal-like order in hard spheres glass transition

TL;DR

This study investigates the roles of icosahedral and crystal-like structural orders in the glass transition of polydisperse hard spheres, finding that crystal-like order correlates with slow dynamics while icosahedral order does not grow in size.

Contribution

It provides experimental evidence that crystal-like order, not icosahedral order, governs slow dynamics near the glass transition in hard sphere systems.

Findings

Crystal-like order grows near the glass transition and is linked to dynamic heterogeneity.

Icosahedral order does not increase in size approaching the glass transition.

Structural order growth is essential for the slowing down of particle dynamics.

Abstract

A link between structural ordering and slow dynamics has recently attracted much attention from the context of the origin of glassy slow dynamics. Candidates for such structural order are icosahedral, exotic amorphous, and crystal-like. Each type of order is linked to a different scenario of glass transition. Here we experimentally access local structural order in polydisperse hard spheres by particle-level confocal microscopy. We identify the key structures as icosahedral and FCC-like order, both statistically associated with slow particles. However, when approaching the glass transition, the icosahedral order does not grow in size whereas crystal-like order grows. It is the latter that governs the dynamics and is linked to dynamic heterogeneity. This questions the direct role of the local icosahedral ordering in glassy slow dynamics and suggests that the growing lengthscale of structural order is essential for the slowing down of dynamics and the nonlocal cooperativity in particle motion.