Motility-induced shear thickening in dense colloidal suspensions

TL;DR

This paper investigates how self-propulsion affects the flow behavior of dense colloidal suspensions, revealing a transition from shear-thinning to shear-thickening due to motility-induced clustering, with implications for tailoring rheology.

Contribution

It introduces the concept of motility-induced shear thickening (MIST) and demonstrates how particle motility can control suspension rheology through clustering effects.

Findings

Self-propulsion lowers the stress barrier for solid-liquid transition.

Turning on motility fluidizes the suspension at low activity.

High motility induces shear thickening via clustering.

Abstract

Phase transitions and collective dynamics of active colloidal suspensions are fascinating topics in soft matter physics, particularly for out-of-equilibrium systems, which can lead to rich rheological behaviours in the presence of steady shear flow. In this article, the role of self-propulsion in the rheological response of a dense colloidal suspension is investigated by using particle-resolved simulations. First, the interplay between activity and shear in the solid to the liquid transition of the suspension is analysed. While both self-propulsion and shear destroy order and melt the system by themselves above their critical values, self-propulsion lowers the stress barrier that needs to be overcome during the transition. Once the suspension reaches a non-equilibrium steady state the rheological response is analysed. While passive suspensions show a solid-like behaviour, turning on particle motility fluidises the system and, at low self-propulsion, the suspension behaves as a shear-thinning fluid. Increasing the self-propulsion of the colloids induces a transition from a shear-thinning to a shear-thickening behaviour, which we attribute to clustering in the suspensions induced by motility. This interesting phenomenon of motility-induced shear thickening (MIST) can be used to tailor the rheological response of colloidal suspensions.