Criteria for Aerodynamically Levitated Droplet on Structured Superhydrophobic Surfaces

Superhydrophobic surfaces exhibit exceptional water-repelling properties due to their low surface energy and micro/nanoscale structures. Understanding droplet motion is crucial for designing self-cleaning materials and fluid manipulation systems. We employ high-speed imaging and interferometry to investigate droplet-surface interactions on structured surfaces, examining how geometric parameters (micro-pillar diameter, height, and pitch) and surface chemistry of the substrate influence aerodynamic levitation. We quantify air-film thickness and friction forces across a velocity range spanning micrometers to centimeters per second, with capillary numbers varying from 10^{-9} to 10^{-3}. Our investigations reveal a velocity-dependent transition: droplets exhibit partial wetting at low velocities but achieve complete levitation at high velocities. This fundamental shift remains poorly understood. Through systematic parametric studies that independently vary geometric properties and surface chemistry, we isolate the individual contributions to wetting transitions. Our results demonstrate that transitions to levitated states can be precisely controlled through strategic substrate modification. These findings provide fundamental insights into droplet dynamics while establishing design principles for advanced liquid-repellent surfaces, advancing both theoretical understanding and practical applications in microfluidics and self-cleaning technologies.