Kinetic Heterogeneities in a Highly Supercooled Liquid

TL;DR

This study uses molecular dynamics to reveal large-scale, critical-like heterogeneities in bond breakage within a highly supercooled two-dimensional liquid, highlighting spatial correlations and evolving weakly bonded regions.

Contribution

It uncovers critical-like spatial heterogeneities in bond breakage events during supercooled liquid relaxation, with detailed analysis of their structure and evolution.

Findings

Bond breakage events occur on the scale of the alpha relaxation time.

Spatial distribution of broken bonds shows critical fluctuation characteristics.

Correlation length of heterogeneities reaches about 100 particle diameters.

Abstract

We study a highly supercooled two-dimensional fluid mixture via molecular dynamics simulation. We follow bond breakage events among particle pairs, which occur on the scale of the $\alpha$ relaxation time $\tau_{\alpha}$. Large scale heterogeneities analogous to the critical fluctuations in Ising systems are found in the spatial distribution of bonds which are broken in a time interval with a width of order $0.05\tau_{\alpha}$. The structure factor of the broken bond density is well approximated by the Ornstein-Zernike form. The correlation length is of order $100 \sigma_1$ at the lowest temperature studied, $\sigma_1$ being the particle size. The weakly bonded regions thus identified evolve in time with strong spatial correlations.