Frost and ice have long been a problem in human society, which may result in disasters, like downed power lines, damaged crops, stalled aircraft, as well as the decreased performance of ships, wind turbines, and heating ventilation and air conditioning (HVAC) systems. Understanding and control of the liquid freezing on solid mediums have a crucial impact on our daily life and industrial production.
The current approach to fabricating anti-frosting surfaces focuses on developing superhydrophobic nanostructures to increase the energy barrier for ice nucleation, and reduce both contact angle hysteresis and the ice adhesion strength. Many studies have shown that superhydrophobic surfaces can successfully prevent icing of individual droplets from being deposited on the surface or impacting the surface at some prescribed velocity. The overall phase change heat transfer on icephobic surfaces, in general, is intentionally sacrificed to suppress the nucleation of water and ice. Therefore, towards energy efficiency of heat transfer devices in frigid environments, a paradoxical issue between anti-icing and condensation enhancement has stumped scientists for years.
At the AECR Lab, we reconcile the conflict between ice inhibition and condensation enhancement by creating a biphilic structural topography. By leveraging the wetting contrast, the patterned hydrophilic structures on superhydrophobic substrates induce a droplet wetting transition, which spontaneously tunes the interfacial thermal barrier and nucleation rates of water and ice in the sequential condensation-freezing process. Owing to the varying interfacial thermal barrier at the liquid-solid interface, the biphilic topography not only reduces the thermal resistance beneath small droplets to enhance the overall heat transfer but also simultaneously retards the heat dissipation of the few anchored large droplets to delay the ice nucleation.
Through a combined experimental and theoretical investigation, we reveal, for the first time, the correlation between the onset of droplet freezing and its characteristic radius. This fundamental study of supercooled condensation freezing offers new insight for controlling the multiphase transitions with surface topography and will guide rational design for more advanced anti-icing materials with high energy efficiency.
