Ultra-low ice-substrate adhesion and self-deicing during droplet impact freezing

A water droplet impacting onto a supercooled surface is typically considered to freeze and adhere to the substrate. This ice accretion poses safety and economic threats to transportation infrastructure, power generation/transmission systems, and telecommunication facilities. Here we report the observation of ultra-low ice-substrate adhesion (0–50 kPa) and remarkable self-deicing during droplet-impact freezing on copper surfaces having medium to high supercooling (30°C–80°C). Mechano-thermo-hydraulic coupling during droplet-impact freezing governs the ice-substrate adhesion by gapping the droplet-substrate contact, enabling self-peeling facilitated by thermal-mechanical stress relaxation. We observe a strong adhesion region in the center of the frozen droplet, which determines the adhesion strength, and develop a regime map to delineate the dependence of adhesion/peeling on droplet inertia, substrate supercooling, and surface wettability. Our work demonstrates key mechanisms governing ice-substrate adhesion during impact icing and presents an approach to passive self-deicing.