Ice-phobic behavior of superhydrophobic Al surface undervarious etching conditions

Abstract

Superhydrophobic Al substrates were fabricated simply by etching pure Al substrates in hot water at 100 °C, followed by hydrophobic coating. The etched/oxidized Al surface layers exhibited spike-like morphologies and superhydrophobicity (corresponding to a water contact angle (CA) of >150°) was induced by surface modification with octadecyltrichlorosilane (OTS). Herein, the ice-repellent behavior of superhydrophobic Al substrates is demonstrated by investigating the CA after applying repeated icing-deicing cycles. The ice-repellent properties were found to be significantly different among apparently similar superhydrophobic surfaces, depending on the Al etching/oxidation and OTS-coating conditions. The loss of hydrophobicity is most likely due to the rupture of Si-O-Al bonds between the OTS molecules and the surface of etched Al, caused by the hydrolysis of these bonds. In freezing delay-time tests, the maximum freezing time of a water droplet was observed on the OTS-coated Al sample with an etching time of 2 h. The Al surface roughness increases with increasing the etching time, then heat is transferred through the water-solid interface area of a water droplet residing on a superhydrophobic surface. Therefore, the larger the surface roughness, the smaller the water-solid contact area, and thus, the larger the amount of entrapped air between water and solid. Therefore, it is very important to find the optimal interfacial bonding conditions between the Al substrate and OTS molecules.