Three-dimensional imaging of colloidal glasses under steady shear

TL;DR

This study uses advanced microscopy to analyze the three-dimensional particle dynamics in a colloidal glass under steady shear, revealing shear thinning behavior and structural relaxation differences from quiescent fluids.

Contribution

It provides the first detailed 3D imaging of colloidal glasses under shear, highlighting shear thinning and relaxation dynamics distinct from quiescent states.

Findings

Structural relaxation is nearly isotropic under shear.

Inverse relaxation time and diffusion constant scale as shear rate to the 0.8 power.

Global rheology exhibits Herschel-Bulkley behavior.

Abstract

Using fast confocal microscopy we image the three-dimensional dynamics of particles in a yielded hard-sphere colloidal glass under steady shear. The structural relaxation, observed in regions with uniform shear, is nearly isotropic but is distinctly different from that of quiescent metastable colloidal fluids. The inverse relaxation time $\tau_\alpha^{-1}$ and diffusion constant $D$, as functions of the {\it local} shear rate $\dot{\gamma}$, show marked shear thinning with $\tau_\alpha^{-1} \propto D \propto \dot{\gamma}^{0.8}$ over more than two decades in $\dot{\gamma}$. In contrast, the {\it global} rheology of the system displays Herschel-Bulkley behavior. We discuss the possible role of large scale shear localization and other mechanisms in generating this difference.