Hovering spreading rebound on porous superhydrophobic surface with active air plastron for rapid drop detachment

Abstract

Superhydrophobic surfaces that promote fast drop detachment have attracted great interests in a wide range of applications such as drag reduction, anti-icing or self-cleaning. Drops impacting on flat superhydrophobic surfaces normally go through lateral spreading, retraction and rebound, with the minimal contact time governed by inertia, viscosity and capillarity. However, under high impacting pressures, the air plastron at the liquid–solid interface would collapse, making the superhydrophobic surfaces unable to rebound impacting drops. Here, we show that a porous superhydrophobic surface with active air plastron can generate a novel bouncing regime: bouncing drops are simultaneously hovering and spreading in the air with rebound occurring far before retraction. The hovering spreading rebound can robustly occur in a wide range of impact velocity, liquid viscosity and drop size. Systematic experimental investigations reveal that this novel bouncing phenomenon results from the balance between inertia and damping force from the air plastron, instead of inertia and capillarity. Our work demonstrates the unexpected effects of active plastron in generating the novel hovering spreading rebound, leading to ∼94% reduction in contact time compared with the conventional complete rebound, which would provide a robust and effective strategy for rapid drop rebound.