Oblique pancake bouncing

Guoqiang Liang

Abstract: Despite extensive efforts in approaching the theoretical limit of solid-liquid contact time, the vertical bouncing droplet eventually lands on the impact spot of horizontally placed surfaces, which makes the liquid removal inefficient and thus limits its practical applications. To address this challenge, we use superhydrophobic surfaces consisting of regularly patterned pillars with an inclined Janus structure and report a phenomenon that involves synergistic effects of both pancake rebound and directional transport in one bouncing cycle, contributing to the reduction of contact time and the lateral removal of impacting droplets simultaneously. We generalize this particular regime to a broad range of working environments with various thermal conditions and impact velocities, demonstrating the robustness of water repellency and the directionality of liquid motion. The unusual bouncing performance, generality, and practicability of our work may provide useful insights into various applications, including electricity generation, self-cleaning, defogging, and anti-icing.