(123a) Collaboration and Competition between Active Sheets for Self-Propelled Particles

Biological species routinely collaborate for their mutual benefit or compete for available resources, thereby displaying dynamic behavior that is challenging to replicate in synthetic systems. Here, we use computational modeling to design microscopic, chemically active sheets and self-propelled particles encompassing the appropriate synergistic interactions to exhibit bio-inspired “feeding”, “fleeing” and “fighting”. This design couples two different mechanisms for chemically generating motion in fluid-filled microchambers: solutal buoyancy and diffusiophoresis. Catalyst-coated sheets, which resemble crabs with four distinct “claws”, convert reactants in solution into products, and thereby create local variations in the density and chemical composition of the fluid. Via the solutal buoyancy mechanism, the density variations generate fluid flows, which modify the shape and motility of the “crabs”. Concomitantly, the chemical variations propel the motion of the particles via diffusiophoresis and thus, the crabs’ and particles’ motion becomes highly interconnected. For crabs with restricted lateral mobility, these two mechanisms can be modulated to either drive a crab to catch and appear to “feed” on all the particles or enable the particles to “flee” from this sheet. Moreover, by adjusting the sheet’s size and the catalytic coating, two crabs can compete and “fight” over the motile, diffusiophoretic particles. Alternatively, the crabs can temporally “share” resources by shuttling the particles back and forth between themselves. With completely mobile sheets, four crabs can collaborate to perform a function that one alone cannot accomplish. These findings provide design rules for creating chemically-driven soft robotic sheets that significantly expand the functionality of microfluidic devices.