Regulation of Droplet Rebound Behavior with Contact Time Control on a Flexible and Superhydrophobic Film.

Rapid droplet detachment from the surface in a "pancake rebound" has recently attracted abundant interest owing to the contact time control for applications in anti-icing and self-cleaning. Even though the pancake rebound on rigid substrates has been realized, the establishment of artificial structures on a flexible counterpart with droplet impact behavior studies has rarely been reported. Here, we introduced a facile approach to fabricating a flexible superhydrophobic film decorated with tunable hierarchical micro/nanostructures for water repellency. With the appropriately optimized architecture, the pancake rebound with reduced contact time can be realized when reaching a specific Weber number on the microcones. We also observed that the pancake rebound on microcilia could be realized by regulating the energy-transfer process on the flexible film during the droplet impact. A tightly stretched and suspended film can serve as the "spring" to store the elastic energy transferred from the kinetic energy of the penetrated droplet while converting back to kinetic energy during the emptying process with a reduced contact time of 5.2 ms. With the preserved water repellency on diverse curvatures, the study raises a new avenue to realize superhydrophobic surfaces and rapid droplet detachment with the potential for a broader spectrum toward practical scenarios in our daily life.