Reciprocal microswimmers in a viscoelastic fluid

TL;DR

This paper explores how certain reciprocal swimming mechanisms enable microswimmers to move in viscoelastic fluids, highlighting the importance of structural asymmetry and specific oscillatory conditions for locomotion.

Contribution

It introduces new reciprocal swimming strategies that achieve locomotion in viscoelastic fluids, emphasizing the role of asymmetry and frequency differences.

Findings

Average velocity depends on the imaginary part of complex shear viscosity.

Structural asymmetry is essential for reciprocal swimming in viscoelastic fluids.

Different oscillatory and size configurations enable movement in such fluids.

Abstract

We suggest several reciprocal swimming mechanisms that lead to a locomotion only in viscoelastic fluids. The first situation is to have a difference between the two amplitudes of the oscillatory arm motion for a three-sphere microswimmer. The second situation is when one of the frequencies of the arm motion is twice as large as the other one for a three-sphere microswimmer. The third situation is when the sphere sizes are different for a two-sphere microswimmer. In all these three cases, the average velocity is proportional to the imaginary part of the complex shear viscosity of a surrounding viscoelastic medium. It is essential for a micromachine to break its structural symmetry in order to swim in a viscoelastic fluid by performing reciprocal body motions.