Structure‐Dependent Optical Modulation of Propulsion and Collective Behavior of Acoustic/Light‐Driven Hybrid Microbowls

Hybrid light/acoustic‐powered microbowl motors, composed of gold (Au) and titanium dioxide (TiO₂) with a structure‐dependent optical modulation of both their movement and collective behavior are reported by reversing the inner and outer positions of Au and TiO₂. The microbowl propels in an acoustic field toward its exterior side. UV light activates the photochemical reaction on the TiO₂ surface in the presence of hydrogen peroxide and the Au/TiO₂ system moves toward its TiO₂ side by self‐electrophoresis. Controlling the light intensity allows switching of the dominant propulsion mode and provides braking or reversal of motion direction when TiO₂ is on the interior, or accelerated motion when the TiO₂ is on its exterior. Theoretical simulations offer an understanding of the acoustic streaming flow and self‐electrophoretic fluid flow induced by the asymmetric distribution of ions around the microbowl. The light‐modulation behavior along with the tunable structure also leads to the control of the swarm behaviors under the acoustic field, including expansion or compaction of ensembles of microbowls with interior and exterior TiO₂, respectively. Such structure‐dependent motion control thus paves the way for a variety of complex microscale operations, ranging from cargo transport to drug delivery in biomedical and environmental applications.