Temporal Light Modulation of Photochemically Active, Oscillating Micromotors: Dark Pulses, Mode Switching, and Controlled Clustering.

Photochemically powered micromotors are prototype microrobots, and spatiotemporal control is pivotal for a wide range of potential applications. Although their spatial navigation has been extensively studied, temporal control of photoactive micromotors remains much less explored. Using Ag-based oscillating micromotors as a model system, a strategy is presented for the controlled modulation of their individual and collective dynamics via periodically switching illumination on and off. In particular, such temporal light modulation drives individual oscillating micromotors into a total of six regimes of distinct dynamics, as the light-toggling frequencies vary from 0 to 103 Hz. On an ensemble level, toggling light at 5 Hz gives rise to controlled, reversible clustering of oscillating micromotors and self-assembly of tracer microspheres into colloidal crystals. A qualitative mechanism based on Ag-catalyzed decomposition of H2O2 is given to account for some, but not all, of the above observations. This study might potentially inspire more sophisticated temporal control of micromotors and the development of smart, biomimetic materials that respond to environmental stimuli that not only change in space but also in time.