Cooperation in binary mixtures of active colloids

The complex interactions underlying collective motion in biological systems give rise to emergent behaviors 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 behaviors, 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 two different metal caps leading to distinct motilities and independently tunable mutual alignment, actuated by AC electric fields. We demonstrate experimentally and numerically that binary mixtures form highly dynamic polar clusters. Moreover, particles segregate according to their motility, leading to cooperative "catch-and-run"-like dynamics in which slow particles are locally advected and pushed by fast polar clusters, producing a transient enhancement of slow-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.