Direct evidence of void induced structural relaxations in colloidal glass formers

TL;DR

This study provides direct experimental evidence that voids in colloidal glasses induce string-like particle motions, revealing the microscopic mechanisms behind structural relaxations in glassy materials.

Contribution

It demonstrates how voids in colloidal glasses facilitate string-like motions, linking microscopic void dynamics to macroscopic relaxation processes.

Findings

Void diffusion into colloidal glasses induces string-like motions.

Quasi-voids are transported by string-like motions in the glass.

Both string-like and compact particle clusters are involved in dynamics.

Abstract

Particle dynamics in supercooled liquids are often dominated by string-like motions in which lines of particles perform activated hops cooperatively. The structural features triggering these motions, crucial in understanding glassy dynamics, remain highly controversial. We experimentally study microscopic particle dynamics in colloidal glass formers at high packing fractions. With a small polydispersity leading to glass-crystal coexistence, a void in the form of a vacancy in the crystal can diffuse reversibly into the glass and further induces string-like motions. In the glass, a void takes the form of a quasi-void consisting of a few neighboring free volumes and is transported by the string-like motions it induces. In fully glassy systems with a large polydispersity, similar quasi-void actions are observed. The mobile particles cluster into string-like or compact geometries, but the compact ones can further be broken down into connected sequences of strings, establishing their general importance.