Preparation and Anti-icing Behavior of Superhydrophobic Surfaces on Aluminum Alloy Substrates

It has been expected that superhydrophohic (SHP) surfacs could have potential anti-icing applications due to their excellent water-repellence properties. However a thorough understanding on the anti-icing performance of such surfaces has never been reported; even systematic characterizations on icing behavior of various surfaces are still rare because of the lack of powerful instrumentations. In this study, we employed the electrochemical anodic oxidation and chemical etching methods to simplify the fabrication procedures for SHP surfaces on the aluminum alloy substrates, aiming at the anti-icing properties of SHP surfaces of various engineering materials. We found that the one-step chemical etching with FeCl3 and HCl as the etchants was the most effective for ideal SHP surfaces with a large contact angle (CA, 159.1 degrees) and a small contact angle hysteresis (CAH, 4.0 degrees). To systematically investigate the anti-icing behavior of the prepared SHP surfaces, we designed a robust apparatus with a real-time control system based on the two stage refrigerating method. This system can monitor the humidity, pressure, and temperature during the icing process on the surfaces. We demonstrated that the SHP surfaces exhibited excellent anti-icing properties, i.e., from the room temperature of 16.0 degrees C, the icing time on SHP surfaces can be postponed from 406s to 676s compared to the normal aluminum alloy surface if the surfaces were put horizontally, and the icing temperature can be decreased from -2.2 degrees C to -6.1 degrees C. If such surfaces were tilted, the sprayed water droplets on the normal surfaces iced up at the temperature of -3.9 degrees C, but bounced off the SHP surface even as the temperature reached as low as -8.0 degrees C. The present study therefore suggests a general, simple, and low-cost methodology for the promising anti-icing applications in various engineering materials and different fields (e.g., power lines and aircrafts).