Chemical Herding: Controlling Collective Behavior of Active Brownian Particles

Programmable control of colloidal particles is important in various micro and nanoscale applications, including dynamic materials, targeted drug delivery, and nanorobotics. Current top-down manipulation methods, such as optical tweezers, offer control over a limited number of particles, restricting their applicability. Alternatively, active matter demonstrates self-assembly of numerous particles, exhibiting intriguing phase behavior such as clustering and collective rotation. However, active matter is more difficult to control. In this study, we hypothesize that introducing a controllable and chemically active "herder" particle to an active matter system will enable us to combine the precision of top-down control methods with the natural collective behavior of active matter. Specifically, we employ 2D Brownian Dynamics simulations to model the dynamic interactions among active Brownian particles. The herder emits a chemical gradient, causing a direct effect on the self-propulsion of surrounding particles. Localized alterations in reactivity result in a distinct phase transition near the herder. By focusing on the collective state of the particle system rather than individual particles, we attain a substantial scaling-up of user control over colloid behavior.