Microscopic Structural Relaxation in a Sheared Supercooled Colloidal Liquid

TL;DR

This study uses confocal microscopy to investigate microscopic structural relaxation and plastic rearrangements in a sheared colloidal suspension, revealing spatially heterogeneous, isotropic dynamics with no directional bias.

Contribution

It provides direct microscopic observations of plasticity and spatial heterogeneity in a sheared colloidal glass, highlighting the isotropic nature of rearrangements.

Findings

Plastic rearrangements are spatially heterogeneous.

Rearrangement regions are isotropic and lack directional alignment.

Particles move randomly without directional bias apart from shear.

Abstract

The rheology of dense amorphous materials under large shear strain is not fully understood, partly due to the difficulty of directly viewing the microscopic details of such materials. We use a colloidal suspension to simulate amorphous materials, and study the shear-induced structural relaxation with fast confocal microscopy. We quantify the plastic rearrangements of the particles in several ways. Each of these measures of plasticity reveals spatially heterogeneous dynamics, with localized regions where many particles are strongly rearranging by these measures. We examine the shapes of these regions and find them to be essentially isotropic, with no alignment in any particular direction. Furthermore, individual particles are equally likely to move in any direction, other than the overall bias imposed by the strain.