The rebounding-coalescing behaviors in drop-on-drop impact on a superhydrophobic surface

The great anti-accumulation performance of drop-on-drop impact on a superhydrophobic surface is beneficial to self-cleaning and anti-icing. Hence, the rebounding-coalescing behaviors in drop-on-drop impingement with varying Weber number and offset ratio are studied experimentally in the present work. The complete regime map of rebounding states is proposed, which can be divided into no-coalesce, jug-like, pancake-like, and pendulum-like rebounding-coalescing behaviors. Subsequently, the increase in the contact time in pendulum-like rebounding-coalescing behaviors is captured and described by a linear model well. Finally, a theoretical prediction based on momentum conservation for the averaged maximal spreading radius of the coalesced droplet is provided. Our approach provides insight into a mechanism of the rebounding-coalescing behaviors, which is helpful for the improvement in related applications.