Propulsion of microspheres by photothermally triggered cavitation bubbles at solid–liquid interfaces

Cavitation bubbles, characterized by their transient and high-energy dynamics, hold great potential for microscale manipulation and propulsion. This study investigates the motion of SiO₂ microspheres driven by cavitation bubbles at solid–liquid interfaces using high-speed imaging and particle image velocimetry. By tuning the cavitation bubble size, microsphere radius, and initial bubble–microsphere distance, controllable unidirectional and reciprocating motions were achieved. Two distinct interaction modes—contact and non-contact—were identified and characterized by the dimensionless parameters δ and ξ. In the contact mode, the cavitation bubble directly interacts with the microsphere, producing stronger propulsion with larger displacements and higher velocities. In contrast, in the non-contact mode, the microsphere is indirectly driven by the fluid motion induced by cavitation bubble dynamics. A force-balance model and numerical simulations further elucidated the underlying mechanisms, revealing that liquid inertia dominates the non-contact mode, whereas asymmetric pressure fields generated during the early bubble growth stage govern the contact mode. This work provides a unified understanding of cavitation-bubble-driven microsphere propulsion, offering insights for controllable micromanipulation and noncontact particle removal.