Swarm Hunting and Clusters Turning Inside Out in Chemically Communicating Active Mixtures

TL;DR

This paper investigates collective behaviors in chemically communicating active mixtures, revealing phases like swarming and core-shell clustering, and demonstrating dynamic cluster inversion, advancing understanding of microorganism-like collective phenomena in synthetic systems.

Contribution

It introduces a minimal physical model combining simulations and stability analysis to explore complex collective behaviors and cluster dynamics in two-species chemotactic active mixtures.

Findings

Identification of a rich phase diagram including hunting swarm and core-shell-cluster phases.

Observation of dynamic cluster inversion or 'species-reversal' phenomena.

Demonstration of collective behaviors previously seen only in large animals, now in simplified active colloids.

Abstract

A large variety of microorganisms produce molecules to communicate via complex signaling mechanisms such as quorum sensing and chemotaxis. The biological diversity is enormous, but synthetic inanimate colloidal microswimmers mimic microbiological communication (synthetic chemotaxis) and may be used to explore collective behaviour beyond the one-species limit in simpler setups. In this work we combine particle based and continuum simulations as well as linear stability analyses, and study a physical minimal model of two chemotactic species. We observed a rich phase diagram comprising a "hunting swarm phase", where both species self-segregate and form swarms, pursuing, or hunting each other, and a "core-shell-cluster phase", where one species forms a dense cluster, which is surrounded by a (fluctuating) corona of particles from the other species. Once formed, these clusters can dynamically turn inside out, representing a "species-reversal". These results exemplify a physical route to collective behaviours in microorganisms and active colloids, which are so-far known to occur only for comparatively large and complex animals like insects or crustaceans.