Dynamics of self-propelled Janus particles in viscoelastic fluids

TL;DR

This study experimentally explores how spherical Janus particles move actively in viscoelastic fluids, revealing a significant increase in rotational diffusion linked to particle velocity and fluid elasticity, affecting their response to external forces.

Contribution

It demonstrates the velocity-dependent enhancement of rotational diffusion in viscoelastic fluids and its impact on microswimmer behavior, a novel insight into active particle dynamics.

Findings

Rotational diffusion increases up to two orders of magnitude with particle velocity.

The effective rotational diffusion coefficient depends on the Weissenberg number.

Microswimmers exhibit anisotropic responses to external forces based on orientation.

Abstract

We experimentally investigate active motion of spherical Janus colloidal particles in a viscoelastic fluid. Self-propulsion is achieved by a local concentration gradient of a critical polymer mixture which is imposed by laser illumination. Even in the regime where the fluid's viscosity is independent from the deformation rate induced by the particle, we find a remarkable increase of up to two orders of magnitude of the rotational diffusion with increasing particle velocity, which can be phenomenologically described by an effective rotational diffusion coefficient dependent on the Weissenberg number. We show that this effect gives rise to a highly anisotropic response of microswimmers in viscoelastic media to external forces depending on its orientation.