Autonomous Formation and Annealing of Colloidal Crystals Induced by Light-Powered Oscillations of Active Particles

Self-organization through communication is observed in many systems throughout nature, often resulting in a collective response to a change in the environment. Herein, we demonstrate a synthetic system that exhibits chemical communication between small active and larger inactive particles which drives the reversible assembly of the latter into colloidal crystals. Specifically, we report the autonomous hexagonal packing of inert silica particles due to the oscillatory behavior of neighboring silver phosphate micromotors under UV light in the presence of hydrogen peroxide. The colloidal crystals are formed under UV illumination and relax into a disordered state when the light is turned off. Furthermore, oscillatory waves generated by the active particles cause “autonomous annealing”, or elimination of defects between crystal boundaries of the silica colloidal crystals.