Vibration-Induced Pancake Bouncing of Impacting Droplets on Hydrophobic Surfaces.

Rapid detachment of impacting droplets from solid surfaces is fundamentally interesting and important in many practical applications, including self-cleaning, anti-icing, and energy harvesting. The droplet pancake bouncing is strongly preferred for the reduced contact time and high bouncing velocity. However, the trigger conditions for pancake bouncing are rigorous. Driven by this, this work circumvents the limitations via solid surface vibration. Our results show that the impacting droplet patterns are highly sensitive to the surface vibration parameters (i.e., the vibration amplitude and frequency), and only a reasonable design of vibration parameters enables the impacting droplets to bounce in a pancake shape without the contraction stage. Intriguingly, the pancake bouncing induced by surface vibration exhibits a significant reduction of solid-liquid contact time (up to ≈80%) compared to the traditional bouncing pattern, and the bouncing velocity has been dramatically enhanced. Furthermore, the critical conditions for the pancake bouncing on the hydrophobic surface and the underlying dynamic mechanism are also identified. This work provides an effective method to achieve well-controlled pancake bouncing of impacting droplets for extensive applications.