Tunable shear thickening in active non-Brownian suspensions

TL;DR

This paper investigates how particle self-propulsion in active suspensions can be used to control shear thickening behavior, revealing a tunable dethickening mechanism that extends existing rheological models.

Contribution

It introduces a simulation study showing that activity can modulate shear thickening, providing a universal scaling framework for active suspension rheology.

Findings

Self-propulsion reduces viscosity at high stress levels.

Dethickening can be tuned via a dimensionless active stress.

Data supports a universal rheological scaling law.

Abstract

We study tunable shear thickening in active suspensions of non-Brownian, repulsive, frictional grains using particle-based simulation, finding that activity augments the rheology beyond the friction-mediated shear thickening paradigm. Specifically, increasing particle self-propulsion drives a viscosity-reducing `dethickening' of the system at large stress, where the material would otherwise be in a thickened, highly viscous state. Self-propulsion introduces additional isotropic dynamics to the particles, which compete with the flow-driven formation of frictional contacts. The degree of dethickening can thus be tuned by varying a suitably-defined dimensionless active stress that quantifies this competition. Recognising the parallels between self-propulsion and other contemporary routes to dethickening, we demonstrate that our data obey a recently proposed scaling framework, supporting a universal description of the tunable rheology of dense suspensions.