Tuning the Viscosity and Jamming Point in Dense Active non-Brownian Suspensions

TL;DR

This study uses simulations to explore how activity influences the flow and jamming behavior of dense non-Brownian suspensions, revealing reduced viscosity, altered force chain structures, and proposing a new rheological model.

Contribution

It introduces a novel simulation framework for active suspensions and uncovers how activity modifies viscosity, jamming, and force chain structures, along with a new constitutive law.

Findings

Activity reduces viscosity by decreasing frictional contacts.

Active particles shift the jamming point to higher volume fractions.

Force chain anisotropy is reduced in active systems.

Abstract

Using numerical simulations, we study the rheological response of dense non-Brownian suspensions containing active particles. The active particles are modelled as run-and-tumble particles with three controlling parameters: the fraction of active particles in the system, an active force applied to the particles, and a persistence time after which the direction of the active force changes randomly. Our simulations reveal that the presence of activity can reduce the viscosity (by an order of magnitude) by decreasing the number of frictional contacts, which also shifts the jamming point to a higher volume fraction. Moreover, the microscopic structure of force chains in the presence of activity is qualitatively different from that in the passive system, showing reduced anisotropy. We also find that while the presence of activity drives the system away from jamming by preventing the formation of force chains, unjamming an already jammed state by breaking existing force chains requires a higher activity strength. Finally, we propose a new constitutive law to describe the rheology of dense active non-Brownian suspensions.