Sessile Droplet Freezing on Hydrophobic Structured Surfaces under Cold Ambient Conditions.

Abstract

There have been conflicting reports as to whether surface wettability is effective for freezing delay enhancement of attached water droplets. It is an important problem in the development of anti-icing surfaces needed for applications, such as aircraft wings and infrastructures. Here, we prepared precooled ambient condition and surfaces which includes smooth, micro-structured, and nanostructured surfaces with hydrophobic coatings to bring it closer to the actual environment and to avoid frost formation which enhance wetting transition and nucleation. Static and dynamic wetting characteristics of each surface were investigated as the fundamental properties and the freezing behavior of precooled water droplet was observed. Distinct elongation of the freezing delay time was observed for droplets on nanostructured surfaces which have static contact angle >150˚, in contrast to the smooth and micro-structured surfaces. However, adhesive property generated by nanostructures showed negligible difference. These results indicated that the reduction of actual contact area between the solid and liquid phases restricted ice nucleus formation.