Relation between local density and density relaxation near glass transition in a glass forming binary mixture

TL;DR

This study uses molecular dynamics simulations to explore how local density influences the slowdown of density relaxation near the glass transition in a binary mixture, revealing a structural basis for the VFT relation.

Contribution

It establishes a link between local density, radial distribution function peaks, and density relaxation, providing a structural explanation for the VFT relation in supercooled liquids.

Findings

Density relaxation time diverges at a critical local density.

Surface density around particles correlates with free volume and dynamics.

The relation resembles the Vogel-Fulcher-Tammann equation, indicating a jamming transition.

Abstract

Many investigations shed light on various correlations between structure and dynamics in supercooled liquids; however, a general relation between structure and dynamics remains elusive. This molecular dynamics simulation study identifies the interrelationship between the growth of the highest peak of the radial distribution function, variation in the radial force from this peak, and the slowdown of the density relaxation in the supercooled states of a model binary glass former. From the microscopic string-like motion in supercooled liquids, we argue that the surface density on a spherical shell around a reference particle at the highest peak of the radial distribution function can represent the free volume available for motion. We further show from these arguments and simulations that density relaxtion time and local density are connected; in this expression, the dynamics diverge at a higher critical value of local density. This relation is similar to the Vogel Fulcher Tammann relation in supercooled liquids, thus giving insight into the structural origin of the VFT as the jamming of particles in a channel of density relaxation.