Characteristics and Mechanisms of Droplets Melting on Superhydrophobic Surfaces

The melting behavior of frozen droplets on superhydrophobic surfaces and their anti-icing mechanisms were systematically investigated via high-speed imaging and quantitative analysis. Two superhydrophobic surfaces (coating-based and etched-based) and a flat control surface were compared to track droplet morphological evolution, solid-liquid interface dynamics, and key metrics under freezing temperatures (–12 to –3°C) and warming conditions (3 to 23°C). Results show that droplets on superhydrophobic surfaces melt from the bottom, forming a tilted, rotating ice cap. The height coefficient decreases continuously (remaining <1) and stabilizes around 0.875,with the coating-type substrate showing the slowest decay (15% reduction over 40 s) versus the control surface, which declines to 0.70 in only 16 s. Contact angle evolution is non-monotonic—initially decreasing, then increasing. Melting on superhydrophobic surfaces lasts 1–2 times longer than on untreated ones. At –9°C freezing and 13°C warming, the coating surface melts the droplet in 98.0 s, versus 42.4 s for the control. This delay is attributed to the “cavitation effect” of micro/nanostructures forming a gas film barrier that reduces solid–liquid heat transfer, along with reduced interfacial tension from low-surface-energy modification. For identical surface chemistry, the coating with a roughness of 6.513 μm exhibits a 30% greater melting time than the Fluorosilane-modified (FGW) surface with a roughness of 0.114 μm. FGWs also outperform stearic acid-modified (SA) surfaces in delaying melting. Two distinct melting modes have been identified: convection-dominated melting on non-superhydrophobic surfaces, and on superhydrophobic ones, rotation-driven melting governed by interfacial tension–buoyancy interplay, often accompanied by bubble release.