Directional Rapid Droplet Bouncing on Flexible Surfaces with Submillimeter Tapered Arrays Enables Rain-Impact Stability in Microfliers

Surfaces designed for directional and rapid liquid transfer hold significant value in various practical applications. Previous research has individually demonstrated either a reduction in contact time by modifying macroscopic solid structures or liquid compositions, or directional rebound through engineered asymmetric surface structures or wetting gradients. However, few studies have achieved both effects simultaneously through a simple and efficient approach. Here, we demonstrate that eyelash-inspired flexible surfaces with submillimeter tapered arrays can generate directional droplet rebound with reduced vertical elongation and reduced contact time of up to 35% compared to conventional vertical rebounds on rigid planes. The asymmetric elongation, horizontal translation, and directional rebound arise from asymmetric capillary forces in the horizontal direction. Furthermore, the penetration of droplets into the submillimeter spacing of the fiber arrays stores capillary energy, which combined with the upward motion of the flexible substrate, facilitates droplet lifting, thereby reducing contact time. The interplay between the structure of flexible surfaces and rebound performance could guide the innovative liquid-repellent design for devices, such as microfliers to maintain stable flight in rain.