Engineering Contactless Particle-Particle Interactions in Active Microswimmers.

Artificial self-propelled colloidal particles have recently served as effective building blocks for investigating many dynamic behaviors exhibited by nonequilibrium systems. However, most studies have relied upon excluded volume interactions between the active particles. Experimental systems in which the mobile entities interact over long distances in a well-defined and controllable manner are valuable so that new modes of multiparticle dynamics can be studied systematically in the laboratory. Here, a system of self-propelled microscale Janus particles is engineered to have contactless particle-particle interactions that lead to long-range attraction, short-range repulsion, and mutual alignment between adjacent swimmers. The unique modes of motion that arise can be tuned by modulating the system's parameters.