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

TL;DR

This paper critiques a prior study on colloidal hard spheres, showing that polydispersity affects the critical packing fraction and that their data mostly align with theoretical predictions, with some exceptions at high densities.

Contribution

It provides a microscopic MCT analysis revealing the impact of polydispersity on the critical packing fraction in colloidal systems.

Findings

Polydispersity shifts the critical packing fraction.

Data generally agree with MCT theory.

Discrepancies observed at the highest packing fractions.

Abstract

In the Letter [PRL 102, 085703 (2009)] Brambilla, et al. claimed to observe activated dynamics in colloidal hard spheres above the critical packing fraction of mode coupling theory (MCT). By performing microscopic MCT calculations, we show that polydispersity in their system shifts the critical packing fraction above the value determined by van Megen et al. for less polydisperse samples, and that the data agree with theory except for, possibly, the highest packing fraction.