Compact nanoscale textures reduce contact time of bouncing droplets

Many natural surfaces are capable of rapidly shedding water droplets-a phenomenon that has been attributed to the presence of low solid fraction textures (Φ_s ~ 0.01). However, recent observations revealed the presence of unusually high solid fraction nanoscale textures (Φ_s ~ 0.25 to 0.64) on water-repellent insect surfaces, which cannot be explained by existing wetting theories. Here, we show that the contact time of bouncing droplets on high solid fraction surfaces can be reduced by reducing the texture size to ~100 nm. We demonstrated that the texture size-dependent contact time reduction could be attributed to the dominance of line tension on nanotextures and that compact arrangement of nanotextures is essential to withstand the impact pressure of raindrops. Our findings illustrate a potential survival strategy of insects to rapidly shed impacting raindrops, and suggest a previously unidentified design principle to engineering robust water-repellent materials for applications including miniaturized drones.