Water droplet bouncing on pre-frosted superhydrophobic carbon soot — A step forward in designing passive icephobic surfaces

Abstract

The devastating repercussions of natural freezing rain phenomena on a variety of industrial facilities might be avoided if the surface-under-attack is designed to be superhydrophobic, thus, repelling the impacting supercooled droplets and remaining free of ice. Regrettably, in climate regions with negative temperatures and highly humid atmosphere, the supersaturated water vapor freezes within the micro- nanocavities of the non-wettable surface and droplet bouncing associated with superhydrophobicity could no longer be preserved. This article explores the possibility of fabricating superhydrophobic carbon soot coatings that would maintain droplet rebound even if their surface is covered with frost. By analyzing the droplet impact dynamics on two groups of frosted soot coatings, differing by morphology, roughness, surface chemistry and porosity, we show for the first time that the liquid meniscus impalement can be cancelled when the soot consists primarily of macropores and oxygen functional groups below 7 at. %. Such a surface configuration ensures minimum energy losses (qualitatively defined) right after the dynamic collision due to the sparsely inceptive ice bridges that normally enhance the heat transfer at the contact interface. The results reported herein could be a useful platform for developing universal icephobic surfaces applicable to harsh environments.