Clustering and Pattern Formation with Chemically Interacting Microswimmers

Chemotaxis is the directed motion of particles in response to a gradient in a chemical signal. It allows micro-organisms, like bacteria, to find food and to escape from toxins. Some micro-organisms can produce the species to which they respond themselves and use chemotaxis for signalling. This can, in the case of chemoattraction where particles migrate up chemical gradients, induce a clustering-instability of the uniform phase and lead to structure formation. This instability currently attracts renewed attention in artificial Janus colloids that swim by catalysing reactions in a chemical bath and show a similar signalling behaviour as micro-organisms.

In this talk, I will demonstrate that also chemorepulsive signalling (where particles migrate away from high chemical density) allows for an instability of the uniform phase. This instability creates a route to the formation of structures such as travelling waves and clusters of self-limiting size which can either be stationary or may oscillate periodically. Finally, I will briefly talk about our latest work on chemotaxis in circularly swimming particles such as bacteria close to walls or synthetic 'L-shaped' colloidal microswimmers.