Segregation and cooperation in active colloidal binary mixtures

TL;DR

This study explores how active colloidal mixtures with different motilities self-organize into segregated and cooperative structures, revealing the roles of motility contrast and alignment in collective behavior.

Contribution

It provides experimental and numerical insights into how motility differences and alignment lead to segregation and cooperation in active colloidal mixtures, a novel exploration of these dynamics.

Findings

Both species form dynamic polar clusters regardless of propulsion speed.

Interspecies interactions cause segregation and cooperative motion.

Transient motility enhancement of slower particles observed.

Abstract

The complex interactions underlying collective motion in biological systems give rise to emergent behaviours such as flocking, sorting, and cooperative transport. These dynamics often involve species with different motilities coordinating movement to optimize navigation and survival. Synthetic analogues based on active colloids offer a controlled platform to explore such behaviours, yet most experimental realizations remain limited to monodisperse systems or mixtures of passive and active particles. Here, we investigate dense binary mixtures of active Janus colloids with distinct motilities and independently tunable alignment, actuated by AC electric fields. We demonstrate experimentally and numerically that both species form highly dynamic polar clusters, with alignment emerging independently of propulsion speed. In mixed populations, interspecies interactions lead to effective segregation and cooperative motion, including transient enhancement of slower particle motility. Our results reveal how motility contrast and alignment combine to drive self-organization in active mixtures, offering strategies for designing reconfigurable materials with collective functionalities.