On Stability and Ice-Releasing Performance of Nanostructured Fluoro-Alkylsilane-Based Superhydrophobic Al alloy2024 Surfaces

Atmospheric icing occurs when surface of exposed structures come into contact with supercooled water droplets and/or snow particles. Ice and wet-snow adhesion and excessive accumulation on exposed structures and equipment is well known as a source of numerous types of failures and malfunctions in power transmission lines, aircrafts, boats etc. in many cold-climate regions. Hydro-/superhydrophobic coatings have been developed over the past few decades as a passive technique to reduce or prevent ice accumulation on outdoor structures. In this study, superhydrophobic Al alloy (AA2024) substrates with static water contact angle values of (CA)>163o and water contact angle hysteresis values of (CAH)≤5o were prepared by etching aluminium alloy substrate in hot water followed by further surface hydrophobization with 1H,1H,2H,2H-perfluorodecyltriethoxysilane (FAS-17) using wet-chemistry technique. The prepared coated Al alloy samples showed good superhydrophobic and self-cleaning properties. Systematic study of both waterand ice-repellent behaviour of such organic coatings terminated by alkyl groups and expected to reduce ice adhesion, were then conducted. The stability tests of the coated surfaces with CA>150o in water resulted in a gradual loss of their superhydrophobic properties after ~1280 h of immersion. Artificially created glaze ice, similar to the naturally accreted one, was deposited on the nanostructured surfaces by spraying supercooled water micro-droplets with the average size of ~80 μm in a wind tunnel at subzero temperature (−10 oC) and a wind speed of 11 m/s. The ice adhesion strength was evaluated by spinning the samples in a centrifuge at constantly increasing speed until ice delaminating occurred. While the uncoated as-received Al alloy samples were found to have an average ice detachment shear stress of ~445±20 kPa, their counterparts coated with a thin layer of FAS-17 showed a lower value of ~65 kPa. This reduction is attributed to the presence of engineered micro/nano-hierarchical surface asperities and to applying low surface energy layers on the sample surfaces. However, the results show that the anti-icing properties of the tested samples deteriorate over time.