Comparison of Dynamical Heterogeneity in Hard-Sphere and Attractive Glass Formers

TL;DR

This study uses molecular dynamics simulations to explore how short-range attractions influence dynamical heterogeneity in glass-forming liquids, revealing significant changes in particle motion behavior with varying attraction strength.

Contribution

It demonstrates that the nature of dynamical heterogeneity varies with attraction strength, highlighting features not captured by conventional theories and supporting models of correlated facilitating defects.

Findings

Weak attractions resemble hard-sphere behavior with punctuated particle motion.

Intermediate attractions suppress distinguishable mobility periods and enhance structural relaxation.

Strong attractions restore bimodal motion but with biased large displacements.

Abstract

Using molecular dynamics simulations, we have determined that the nature of dynamical heterogeneity in jammed liquids is very sensitive to short-ranged attractions. Weakly attractive systems differ little from dense hard-sphere and Lennard-Jones fluids: Particle motion is punctuated and tends to proceed in steps of roughly a single particle diameter. Both of these basic features change in the presence of appreciable attractions. Transient periods of particle mobility and immobility cannot be discerned at intermediate attraction strength, for which structural relaxation is greatly enhanced. Strong attractions, known to dramatically inhibit relaxation, restore bimodality of particle motion. But in this regime, transiently mobile particles move in steps that are significantly more biased toward large displacements than in the case of weak attractions. This modified feature of dynamic heterogeneity, which cannot be captured by conventional mode coupling theory, verifies recent predictions from a model of spatially correlated facilitating defects.