The glass transition of two-dimensional binary soft disk mixtures with large size ratios

TL;DR

This study explores how the dynamics of two-dimensional binary soft disk mixtures slow down near the glass transition, revealing that large particle distribution influences fragility more than structural order at high size ratios.

Contribution

It demonstrates that for large size ratios, fragility correlates with large particle distribution rather than structural ordering, highlighting the role of confinement in glassy dynamics.

Findings

Fragility depends on mixture composition and large particle distribution.

Structural ordering is not correlated with fragility at high size ratios.

Large particles act as confining walls affecting dynamical heterogeneity.

Abstract

We simulate binary soft disk systems in two dimensions, and investigate how the dynamics slow as the area fraction is increased toward the glass transition. The "fragility" quantifies how sensitively the relaxation time scale depends on the area fraction, and the fragility strongly depends on the composition of the mixture. We confirm prior results for mixtures of particles with similar sizes, where the ability to form small crystalline regions correlates with fragility. However, for mixtures with particle size ratios above 1.4, we find that the fragility is not correlated with structural ordering, but rather with the spatial distribution of large particles. The large particles have slower motion than the small particles, and act as confining "walls" which slow the motion of nearby small particles. The rearrangement of these confining structures governs the lifetime of dynamical heterogeneity, that is, how long local regions exhibit anomalously fast or slow behavior. The strength of the confinement effect is correlated with the fragility and also influences the aging behavior of glassy systems.