Self-Adaptive Droplet Bouncing on a Dual Gradient Surface

Rapid detachment of impacting droplets from underlying substrate is highly preferred for mass, momentum, and energy exchange in many practical applications. Driven by this, the past several years have witnessed a surge in engineering macrotexture to reduce solid-liquid contact time. Despite these advances, these strategies in reducing contact time necessitate the elegant control of either the spatial location for droplet contact or the range of impacting velocity. Here, this work circumvents these limitations by designing a dual gradient surface consisting of a vertical spacing gradient made of tapered pillar arrays and a lateral curvature gradient characterized as macroscopic convex. This design enables the impacting droplets to self-adapt to asymmetric or pancake bouncing mode accordingly, which renders significant contact time reduction (up to approximate to 70%) for a broad range of impacting velocities (approximate to 0.4-1.4 m s-1) irrespective of the spatial impacting location. This new design provides a new insight for designing liquid-repellent surfaces, and offers opportunities for applications including dropwise condensation, energy conversion, and anti-icing. Despite notable progress in reducing solid-liquid contact time through surface engineering, existing methods suffer from one or more limitations. Here, this work reports the adaptive droplet bouncing on the curved islands made of tapered cones to eliminate these intractable conundrums, which unprecedentedly reduce contact time by approximate to 70% at higher Weber numbers We and approximate to 20% at low We simultaneously.image