Physical aging and relaxation of residual stresses in a colloidal glass following flow cessation

TL;DR

This study explores how flow history influences residual stresses and aging dynamics in colloidal glasses, revealing that quench rate affects stress relaxation and aging speed, with slower quenches leading to more jammed states and slower aging.

Contribution

It establishes a direct link between flow cessation conditions and the subsequent aging behavior in colloidal glasses, highlighting the role of residual stresses.

Findings

Faster quenches lead to smaller, quickly relaxing residual stresses.

Slower quenches produce more jammed states with slower stress relaxation.

Residual stress relaxation time scales inversely with quench rate.

Abstract

Dilute Laponite suspensions in water at low salt concentration form repulsive colloidal glasses which display physical aging. This phenomenon is still not completely understood and in particular, little is known about the connection between the flow history, as a determinant of the initial state of the system, and the subsequent aging dynamics. Using a stress controlled rheometer, we perform stress jump experiments to observe the elastic component of the flow stress that remains on cessation of flow or flow quenching. We investigate the connection between the dynamics of these residual stresses and the rate of physical aging upon quenching from different points on the steady state flow curve. Quenching from high rates produces a fluid state, G">G', with small, fast relaxing residual stresses and rapid, sigmoidal aging of the complex modulus. Conversely, quenching from lower shear rates produces increasingly jammed states featuring slowly relaxing stresses and a slow increase of the complex modulus with system age. Flow cessation from a fixed shear rate with varying quench durations shows that slower quenches produce smaller residual stresses at short times which relax at long times by smaller extents, by comparison with faster quenches. These smaller stresses are correlated with a higher modulus but slower physical aging of the system. The characteristic time for the residual stress relaxation scales inversely with the quench rate. This implies a frustrated approach to any ideal stress-free state that succinctly reflects the frustrated nature of these glassy systems.