Theory of activated-rate processes under shear with application to shear-induced aggregation of colloids

TL;DR

This paper develops a theoretical framework extending Kramers theory to describe shear-driven aggregation in colloids, explaining experimental observations of viscosity increase and unveiling the role of shear in activated-rate processes.

Contribution

It introduces a novel approximation scheme within the convective diffusion framework, providing the first analytical model linking shear to activated aggregation in soft matter.

Findings

Theory explains shear-induced aggregation and viscosity rise.

Verification against experiments and numerics supports the model.

Shear significantly influences activation rates in colloidal systems.

Abstract

Using a novel approximation scheme within the convective diffusion (two body Smoluchowski) equation framework, we unveil the shear-driven aggregation mechanism at the origin of structure-formation in sheared colloidal systems. The theory, verified against numerics and experiments, explains the induction time followed by explosive (irreversible) rise of viscosity observed in charge-stabilized colloidal and protein systems under steady shear. The Arrhenius-type equation with shear derived here, extending Kramers theory in the presence of shear, is the first analytical result clearly showing the important role of shear-drive in activated-rate processes as they are encountered in soft condensed matter.