Reducing the contact time of impacting water drops on superhydrophobic surfaces by liquid-like coatings

Abstract

Surfaces that can rapidly shed impacting drops are important for a wide range of applications, including anti-icing, dropwise condensation and miniaturized drones. Previous strategies to reduce the contact time of impacting drops are primarily based on engineering superhydrophobic surfaces through introducing secondary textures, either macroscopic or nanoscopic, or constructing specifically designed nanotextures. Here, a facile and effective approach is demonstrated to reduce the contact time of superhydrophobic surfaces by simply replacing the widely used perfluorosilane (i.e., trichloro (1H, 1H, 2H, 2H-perfluorooctyl) silane, PFOS) coating with liquid-like perfluorinated polyether (PFPE) surface chemistry. Though their apparent contact angles are comparable, the PFPE-coated superhydrophobic surface exhibits a reduction of contact time up to 26% compared to the PFOS-coated counterpart, attributed to enhanced retraction speed on the former surface. Remarkably, while a classical inertial model predicts a merely 3% difference in retraction time between the PFPE- and the PFOS-coated surfaces, a drastic reduction of retraction time by 12–32% is observed. The improved retraction dynamics on the liquid-like surface is suggested to be caused by the low contact angle hysteresis and enhanced interface slippage on the liquid-like coating. This study offers a general strategy to enhance dynamic liquid repellency of superhydrophobic surfaces for diverse applications.