Competition and Cooperation among Chemically Active Sheets and Particles

Using theory and simulation, we model the interactions among different, chemically active objects in a fluid-filled microchamber to establish conditions that drive these synthetic objects to display biomimetic competitive or cooperative behavior. The first objects are catalyst-coated, flexible sheets that generate buoyancy-driven fluid flows. The second objects are mobile tracer particles that move via diffusiophoresis towards higher reactant concentrations. We vary the sheets’ size and areal concentration of catalyst to tune the rate of reaction at this layer. Through these studies, we determine regions in phase space that lead to “aggressive” competition or “beneficial” cooperation within this dynamic, non-equilibrium system. As an example of competition, we show that when a low concentration of reactants is introduced into the solution, the larger sheet “catches” more tracers than a smaller sheet with a higher areal concentration of catalyst. Furthermore, we isolate conditions where single sheets acting alone do not capture tracers, but can trap the motile particles through cooperative interactions. These studies illustrate how purely physicochemical factors can promote behavior highly reminiscent of biological systems among active objects in fluidic environments.