Marangoni Flow Induced Collective Motion of Catalytic Micromotors

A new collective motion of non-bubble-propelled spherical Janus catalytic micromotors has been observed. When the local concentration of micromotors is high, bubbles start to form between the motors. As the bubble grows, micromotors move collectively toward the center of the bubble regardless of the orientations of their catalyst surface, eventually become aggregated, and captured around the perimeter of the bubble. It is suggested that this collective motion of the micromotors, too fast for the diffusiophoresis, can be caused by the entrainment of micromotors by the evaporation-induced Marangoni flow near the bubble. Numerical simulations confirmed that the direction and strength of such Marangoni flow are consistent with the fast, collective motion of micromotors observed experimentally.