Hydrodynamic and contact contributions to shear thickening in colloidal suspensions

TL;DR

This study uses shear reversal experiments and simulations to determine that contact forces, especially frictional interactions, primarily cause shear thickening in colloidal suspensions, challenging the traditional hydrodynamic cluster view.

Contribution

The paper provides direct experimental evidence that contact forces dominate shear thickening, supported by simulations highlighting frictional interactions as key contributors.

Findings

Contact forces dominate shear thickening in colloidal suspensions.

Frictional interactions are the primary source of contact forces.

Shear reversal experiments effectively distinguish hydrodynamic and contact contributions.

Abstract

Shear thickening is a widespread phenomenon in suspension flow that, despite sustained study, is still the subject of much debate. The longstanding view that shear thickening is due to hydrodynamic clusters has been challenged by recent theory and simulations suggesting that contact forces dominate, not only in discontinuous, but also in continuous shear thickening. Here, we settle this dispute using shear reversal experiments on micron-sized silica and latex colloidal particles to measure directly the hydrodynamic and contact force contributions to shear thickening. We find that contact forces dominate even continuous shear thickening. Computer simulations show that these forces most likely arise from frictional interactions.