Interaction between cavitation bubbles and plastrons on superhydrophobic surfaces

The interaction between cavitation bubbles and plastrons on superhydrophobic surfaces was investigated using a low-voltage discharge device and high-speed photography techniques. The plastron adhered to the superhydrophobic surface acts as a liquid-gas interface, giving the boundary the ability to repel cavitation bubbles. The direction of bubble collapse is determined by the vector synthesis of the Bjerknes repulsive force from the plastron and the Bjerknes attractive force from the rigid wall when the bubble collapses for the first time. Various collapse behaviors were observed, including bubbles moving away from the plastron, bubbles orienting towards the plastron, and bubbles splitting into sub-bubbles in opposite directions. During the subsequent evolution of the bubbles, the expansion of the plastron led to the reversal of the downward jet or reduced the impact velocity of the jet. Seven jet patterns were identified based on the evolution of the cavitation bubble. Starting from the impact velocity of the jet, three jet patterns, namely, the jet away from the plastron (JA), the funnel-shaped jet away from the plastron (JAF), and the funnel-shaped jet away from the plastron with vortex shedding (JAFV), were found to have a weaker effect on the boundary. Three criteria for the design of plastrons on superhydrophobic surfaces were established: V-P > 0.25V(max), H-P > 0.55R(max), D-P > 1.2R(max). Passive pulsation of the plastron in response to the cavitation bubble exhibited similar behaviors across seven jet patterns except for the JAF pattern: torus-shaped, dish-shaped, and skirt-shaped. The dimensionless wall distance, volume ratio, and plastron morphology parameters were identified as significant factors influencing the interaction between cavitation bubbles and the plastron.