Non-Newtonian effects on the slip and mobility of a self-propelling active particle

TL;DR

This paper investigates how non-Newtonian fluid properties like viscoelasticity and shear-thinning affect the slip velocity and mobility of active Janus particles, providing analytical insights and implications for complex fluid transport.

Contribution

It offers the first analytical expression for non-Newtonian modifications to diffusio-osmotic slip on active surfaces, linking fluid rheology to particle mobility.

Findings

Polymer elasticity modifies slip velocity proportional to the second tangential derivative of concentration.

Non-Newtonian effects influence the mobility of Janus spheres.

Results have implications for transport in diffusio-osmotic pumps.

Abstract

Janus particles propel themselves by generating concentration gradients along their active surface. This induces a flow near the surface, known as the diffusio-osmotic slip, which propels the particle even in the absence of externally applied concentration gradients. In this work, we study the influence of viscoelasticity and shear-thinning (described by the second-order-fluid and Carreau model, respectively) on the diffusio-osmotic slip on an active surface. Using matched asymptotic expansions, we provide an analytical expression for the modification of slip induced by the non-Newtonian behavior. The results reveal that the modification in slip velocity arising from polymer elasticity is proportional to the second tangential derivative of the concentration field. Using the reciprocal theorem, we estimate the influence of this modification on the mobility of a Janus sphere. The current study also has direct implications on the understanding of the transport of complex fluids in diffusio-osmotic pumps.