A three-sphere microswimmer in a structured fluid

TL;DR

This paper analyzes how a three-sphere microswimmer moves in a structured viscoelastic fluid, deriving a general velocity expression and exploring effects of fluid and swimmer symmetry breaking, with detailed examples in polymer gels.

Contribution

It provides a general expression linking swimming velocity to sphere mobilities in structured fluids, considering both viscous and elastic effects, and explores the impact of fluid and swimmer symmetry breaking.

Findings

Viscous contribution arises when time-reversal symmetry is broken.

Elastic contribution appears when the swimmer's structural symmetry is broken.

Competition between swimmer size and polymer mesh size leads to complex dynamics.

Abstract

We discuss the locomotion of a three-sphere microswimmer in a viscoelastic structured fluid characterized by typical length and time scales. We derive a general expression to link the average swimming velocity to the sphere mobilities. In this relationship, a viscous contribution exists when the time-reversal symmetry is broken, whereas an elastic contribution is present when the structural symmetry of the microswimmer is broken. As an example of a structured fluid, we consider a polymer gel, which is described by a "two-fluid" model. We demonstrate in detail that the competition between the swimmer size and the polymer mesh size gives rise to the rich dynamics of a three-sphere microswimmer.