Pancake bouncing on superhydrophobic surfaces

TL;DR

This paper introduces a novel superhydrophobic surface design that enables pancake bouncing, significantly reducing drop contact time and enhancing drop detachment efficiency for applications like anti-icing and self-cleaning.

Contribution

The study demonstrates how patterned superhydrophobic surfaces with nano-textures induce pancake bouncing, a new regime that reduces contact time and is robust across various impact velocities.

Findings

Pancake bouncing reduces contact time fourfold compared to conventional rebound.

Surface micro/nanotextures act as harmonic springs, making bounce behavior velocity-independent.

Design enables rapid drop detachment over a wide range of impact velocities.

Abstract

Engineering surfaces that promote rapid drop detachment is of importance to a wide range of applications including anti-icing, dropwise condensation6, and self-cleaning. Here we show how superhydrophobic surfaces patterned with lattices of submillimetre-scale posts decorated with nano-textures can generate a counter-intuitive bouncing regime: drops spread on impact and then leave the surface in a flattened, pancake shape without retracting. This allows for a four-fold reduction in contact time compared to conventional complete rebound. We demonstrate that the pancake bouncing results from the rectification of capillary energy stored in the penetrated liquid into upward motion adequate to lift the drop. Moreover, the timescales for lateral drop spreading over the surface and for vertical motion must be comparable. In particular, by designing surfaces with tapered micro/nanotextures which behave as harmonic springs, the timescales become independent of the impact velocity, allowing the occurrence of pancake bouncing and rapid drop detachment over a wide range of impact velocities.