Particulate Projectiles Driven by Cavitation Bubbles

The removal of surface-attached particles with cavitation bubbles is usually attributed to the jetting or shear stresses when bubbles collapse. In this Letter, we report an unexpected phenomenon that millimeter-sized spherical particles made of heavy metals (e.g., stainless steel), when initially resting on a fixed rigid substrate, are suddenly accelerated like projectiles through the production of nearby laser-induced cavitation bubbles of similar sizes. We show experimentally and theoretically that the motion of a particle with radius Rp is determined by the maximum bubble radius Rb;max, the initial distance from the laser focus to the center of the particle L0, and the initial azimuth angle phi 0. We identify two dominant regimes for the particle's sudden acceleration, namely, the unsteady liquid inertia dominated regime and the bubble contact dominated regime, determined by Rb;maxRp=L20. We find the nondimensional maximum vertical displacement of the particle follows the fourth power and the square power scaling laws for respective regimes, which is consistent with the experimental results. Our findings can be applied to nonintrusive particle manipulation from solid substrates in a liquid.

Automated summary

This paper reports an unexpected phenomenon that laser-induced cavitation bubbles can cause sudden acceleration of heavy metal particles resting on a fixed substrate. Experimental and theoretical analysis reveal the factors influencing the acceleration of the particles.