Roughness Induced Rotational Slowdown Near the Colloidal Glass Transition

TL;DR

This study reveals that surface roughness in spherical colloids induces a second glass transition, significantly affecting their rotational dynamics and interlocking contacts, as shown through 3D confocal microscopy.

Contribution

It uncovers a previously unreported second glass transition in rough colloids caused by interlocking contacts restricting rotation.

Findings

Roughness lowers the translational glass transition concentration.

A broad concentration range shows a shift from diffusive to rattling rotational motion.

Interlocking contacts restrict particle rotations, leading to a second glass transition.

Abstract

Roughening the surface of spherical colloids can drastically change their translational and rotational dynamics in dense suspensions. Using 3D confocal microscopy, we show that roughness not only lowers the concentration of the translational colloidal glass transition, but also generates a broad concentration range in which the rotational Brownian motion changes signature from high-amplitude diffusive to low-amplitude rattling. This hitherto not reported second glass transition for rough spherical colloids emerges when the particle intersurface distance becomes comparable to the roughness length scale. Interlocking contacts are responsible for restricting the particle rotations.