Probing the equilibrium dynamics of colloidal hard spheres above the mode-coupling glass transition

TL;DR

This study investigates the equilibrium dynamics of colloidal hard spheres at high densities, revealing a new dynamical regime above the glass transition where relaxation times grow unexpectedly and heterogeneity increases slowly.

Contribution

It provides the first comprehensive analysis of equilibrium dynamics above the mode-coupling glass transition in colloidal suspensions, combining experiments and simulations over an extensive density range.

Findings

System remains ergodic above the glass transition density.

Relaxation time increases with an unanticipated functional form.

Dynamic heterogeneity grows slower than a power law with relaxation time.

Abstract

We use dynamic light scattering and computer simulations to study equilibrium dynamics and dynamic heterogeneity in concentrated suspensions of colloidal hard spheres. Our study covers an unprecedented density range and spans seven decades in structural relaxation time, $\ta$, including equilibrium easurements above $\phi_{\rm c}$, the location of the glass transition deduced from fitting our data to mode-coupling theory. Instead of falling out of equilibrium, the system remains ergodic above $\phi_{\rm c}$ and enters a new dynamical regime where $\ta$ increases with a functional form that was not anticipated by previous experiments, while the amplitude of dynamic heterogeneity grows slower than a power law with $\ta$, as found in molecular glass-formers close to the glass transition.