Rheological properties of a dilute suspension of self-propelled particles

TL;DR

This paper models the rheological behavior of dilute suspensions of self-propelled particles, revealing activity-dependent viscosity changes and non-Newtonian effects at small Peclet numbers.

Contribution

It introduces a microscopic model linking swimmer activity to suspension rheology, highlighting activity's impact on effective viscosity and normal stress differences.

Findings

Self-propelled particles alter suspension viscosity based on their pushers or pullers nature.

Activity induces non-Newtonian behavior with normal stress differences.

Effective viscosity deviates from classical predictions due to swimmer activity.

Abstract

With a detail microscopic model for a self-propelled swimmer, we derive the rheological properties of a dilute suspension of such particles at small Peclet numbers. It is shown that, in addition to the Einstein's like contribution to the effective viscosity, that is proportional to the volume fraction of the swimmers, a contribution due to the activity of self-propelled particles influences the viscosity. As a result of the activity of swimmers, the effective viscosity would be a lower (higher) than the viscosity of the suspending medium when the particles are pushers (pullers). Such activity dependent contribution, will also results to a non-Newtonian behavior of the suspension in the form of normal stress differences.