The glass transition of dense fluids of hard and compressible spheres

TL;DR

This study uses simulations to investigate the glass transition in dense, polydisperse spheres, revealing evidence of avoided singularities and multiple jamming points, and proposing an ideal glass transition at a specific density.

Contribution

It provides new insights into the glass transition of dense spheres, including the estimation of the equation of state and the existence of multiple jamming densities.

Findings

Evidence of avoided mode-coupling singularity near phi_MCT ~ 0.592

Divergence of relaxation times at phi_0 ~ 0.635

Multiple equations of state for glasses above phi_0

Abstract

We use computer simulations to study the glass transition of dense fluids made of polydisperse, repulsive spheres. For hard particles, we vary the volume fraction, phi, and use compressible particles to explore finite temperatures, T>0. In the hard sphere limit, our dynamic data show evidence of an avoided mode-coupling singularity near phi_{MCT} ~ 0.592, they are consistent with a divergence of equilibrium relaxation times occurring at phi_0 ~ 0.635, but they leave open the existence of a finite temperature singularity for compressible spheres at volume fraction phi > phi_0. Using direct measurements and a new scaling procedure, we estimate the equilibrium equation of state for the hard sphere metastable fluid up to phi_0, where pressure remains finite, suggesting that phi_0 corresponds to an ideal glass transition. We use non-equilibrium protocols to explore glassy states above phi_0 and establish the existence of multiple equations of state for the unequilibrated glass of hard spheres, all diverging at different densities in the range phi \in [0.642, 0.664]. Glassiness thus results in the existence of a continuum of densities where jamming transitions can occur.