Aging under Shear: Structural Relaxation of a Non-Newtonian Fluid

TL;DR

This study investigates how shear influences the aging dynamics of a colloidal suspension, revealing a transition between aging regimes and quantifying shear's effect on relaxation times and autocorrelation functions.

Contribution

It introduces a quantitative model describing the shear-dependent relaxation process in aging colloidal suspensions, highlighting the heterogeneous nature of relaxation under shear.

Findings

Transition between aging regimes as relaxation time approaches inverse shear rate

Strong sensitivity of relaxation time to shear rate in shear-dominated regime

Quantitative description of autocorrelation function shape under shear

Abstract

The influence of an applied shear field on the dynamics of an aging colloidal suspension has been investigated by the dynamic light scattering determination of the density autocorrelation function. Though a stationary state is never observed, the slow dynamics crosses between two different non-equilibrium regimes as soon as the structural relaxation time approaches the inverse shear rate. In the shear dominated regime (at high shear rate values) the structural relaxation time is found to be strongly sensitive to shear rate while aging proceeds at a very slow rate. The effect of shear on the detailed shape of the density autocorrelation function is quantitatively described assuming that the structural relaxation process arises from the heterogeneous superposition of many relaxing units each one independently coupled to shear with a parallel composition rule for timescales.