How surface charges affect interdroplet freezing.

The freezing of droplets on surfaces is closely relevant with various industrial processes such as aviation, navigation, and transportation. Previous studies mainly focus on physiochemically heterogeneous but electrically homogeneous surfaces, on which the presence of vapor pressure gradient between droplets is the predominant mechanism for interdroplet freezing bridging, propagation, and eventual frosting across the entire surface. An interesting yet unanswered question is whether electrostatic charge on surfaces affects freezing dynamics. Here, we find an interdroplet freezing relay (IFR) phenomenon on electrically heterogeneous surfaces that exhibits a three-dimensional, in-air freezing propagation pathway and an accelerated freezing rate. Theoretical and experimental investigations demonstrate that this phenomenon originates from the presence of surface charge gradient established between the frozen droplet and neighboring water droplet, which leads to a spontaneous shooting of desublimated ice needles from the frozen droplet and then triggers the freezing of neighboring water droplet in in-air manner. We further demonstrate its generality across various dielectric substrates, liquids, and droplet configurations. Our work enriches conventional perspectives on droplet freezing dynamics and emphasizes the pivotal role of electrostatics in designing passive anti-icing and antifrosting materials.