Roughness-engineered potential wells for controllable ultrasonic cavitation: Multistage bubble capture-release mechanism revealed by multiscale experiments and simulations.

Controlling cavitation dynamics is essential for optimizing ultrasonic-assisted processing, targeted energy release, and damage mitigation. Here, we propose a structural strategy for tunable cavitation control using roughness-engineered surfaces that generate geometry-induced potential wells. Titanium alloy walls with varying porosity were fabricated via triply periodic minimal surface designs to systematically modulate roughness. High-speed imaging revealed that moderate roughness stabilizes bubble aggregation above the surface, whereas smooth walls fail to retain bubbles and excessive roughness induces perturbation-driven release. Specifically, in the 20 % porosity sample at t = 0.78 ms, multiple larger clusters formed at the center region of the wall, displaying asymmetric shapes and stretched edges, significantly increasing bubble retention time. Molecular dynamics simulations demonstrated that van der Waals-dominated short-range adsorption and localized low-energy zones extend bubble residence time, enabling stable capture. Excessive roughness, however, disrupts potential well uniformity, triggering asymmetric collapse and directed energy release. Integrating experimental and simulation results, we establish a multistage "capture-perturbation-collapse-release" framework for surface-induced cavitation control. This approach could potentially enable targeted cavitation control in ultrasonic cleaning, precision machining, and erosion prevention.