Delayed Frost Growth on Jumping-Drop Superhydrophobic Surfaces

1. CNMS Staff Science Highlight Delayed Frost Growth on Jumping-Drop Superhydrophobic Surfaces • Scientific Achievement • On a subzero super-hydrophobic surface having both microscopic and nanoscopicroughness, self-propelled jumping water drops slow down condensation frosting significantly when compared to a smooth hydrophobic surface. Jumping drops prevent heterogeneous ice nucleation by continuously removing sub-cooled condensate, and by minimizing ice bridge formation between drops. • Significance • The jumping-drop effect has not been reported previously for frost formation on sub-cooled surfaces. While previous reports have focused exclusively on liquid-solid ice nucleation for isolated drops, we find for the first time that frost growth across the surface is an inter-drop phenomenon that is significantly affected by jumping drops. • Research Details • Condensation frosting on was studied by cooling both hydrophobic and superhydrophobic surfaces with a Peltier stage down to -20°C. • Condensation frosting on both hydrophobic and superhydrophobic surfaces was characterized by measuring drop diameters and inter-drop separation distances. • A simple scaling model was developed that related the success and speed of inter-drop ice bridging to the drop size distribution. #5 1.4 nm Ice bridge growth from a frozen drop to neighboring liquid drops on a hydrophobic surface chilled to -20° C. (A) When liquid drops were close to a frozen drop, the ice bridge connected to the liquid drops and immediately froze them. (B) For liquid drops that were small and/or far away from a frozen drop, the liquid drop evaporated before a bridge could connect. (C) Schematic of the process. Histograms of liquid droplet diameters for both hydrophobic (HPB) and superhydrophobic (SHPB) surfaces during ice bridge growth. SHPB surfaces have smaller size distributions, which delays ice bridge growth. J.B. Boreyko and C.P. Collier, ACS Nano. DOI:10.1021/nn3055048 (2013)