Inspired by the collective behavior of natural living systems, the collective behavior of micromotors has become the research highlight. Although great progress has been made, it is still challenging to control the collective behavior of micromotors. In this paper, we demonstrate a novel near-infrared (NIR) light-powered micromotor consisting of a polystyrene microsphere and a polydopamine core-shell structure (PS@PDA) with concentration-dependent motion direction reversal and dynamic swarming behavior. Among others, a single micromotor exhibits negative phototaxis, whereas a group of micromotors shows positive phototaxis, which can be attributed to the competition between the thermophoretic force and hydrodynamic drag caused by the thermal buoyancy. In addition, because of the reversible hydrogen bonding and π-π stacking interactions between the adjacent PS@PDA micromotors, they form aggregation as a result of the positive phototaxis with dynamically controllable shapes tuned by the irradiation position, which makes them potentially attractive for in-solution calligraphy and painting. It is anticipated that the current study may not only provide a new strategy to control the collective behavior of the micromotors, but also promote their application in the practical field.
Keywords: dynamic collective behavior; light-driven; micromotor; phototaxis; self-propulsion.