Stress-activated Constraints in Dense Suspension Rheology

TL;DR

This paper presents a simulation-based framework that explains shear-thickening and shear jamming in dense suspensions through stress-activated constraints on particle contact movements, linking microscopic forces to macroscopic rheology.

Contribution

It introduces a simplified model focusing on sliding and rolling constraints that accurately reproduces experimental shear thickening across diverse systems.

Findings

Constraints on sliding and rolling reproduce shear thickening.

Parameters correlate with microscopic force origins.

Framework links micro-scale forces to macro-scale rheology.

Abstract

Dispersing small particles in a liquid can produce surprising behaviors when the solids fraction becomes large: rapid shearing drives these systems out of equilibrium and can lead to dramatic increases in viscosity (shear-thickening) or even solidification (shear jamming). These phenomena occur above a characteristic onset stress when particles are forced into frictional contact. Here we show via simulations how this can be understood within a framework that abstracts details of the forces acting at particle-particle contacts into general stress-activated constraints on relative particle movement. We find that focusing on just two constraints, affecting sliding and rolling at contact, can reproduce the experimentally observed shear thickening behavior quantitatively, despite widely different particle properties, surface chemistries, and suspending fluids. Within this framework parameters such as coefficients of sliding and rolling friction can each be viewed as a proxy for one or more forces of different physical or chemical origin, while the parameter magnitudes indicate the relative importance of the associated constraint. In this way, a new link is established that connects features observable in macroscale rheological measurements to classes of constraints arising from micro- or nano-scale properties.