An active particle in a complex fluid

TL;DR

This paper investigates how active particles, specifically Janus particles, move in complex non-Newtonian fluids, revealing that viscoelasticity can either speed up or slow down the particle, while shear-thinning always slows it down.

Contribution

It introduces a method to analyze active particle motion in non-Newtonian fluids using the reciprocal theorem and quantifies the effects of viscoelasticity and shear-thinning on particle speed.

Findings

Janus particles can move faster or slower in viscoelastic fluids.

In shear-thinning fluids, Janus particles are always slower compared to Newtonian fluids.

The study provides insights into particle dynamics in complex rheological environments.

Abstract

In this work, we study active particles with prescribed surface velocities in non-Newtonian fluids. We employ the reciprocal theorem to obtain the velocity of an active spherical particle with an arbitrary axisymmetric slip-velocity in an otherwise quiescent second-order fluid. We then determine how the motion of a diffusiophoretic Janus particle is affected by complex fluid rheology, namely viscoelasticity and shear-thinning viscosity, compared to a Newtonian fluid, assuming a fixed slip-velocity. We find that a Janus particle may go faster or slower in a viscoelastic fluid, but is always slower in a shear-thinning fluid as compared to a Newtonian fluid.