G. Boveri, M. Raimondo, F. Veronesi, A. Corozzi
Institute of Science and Technology for Ceramics ISTEC CNR,
Keywords: superhydrophobicity, contact angle hysteresis, anti-icing, subzero temperature applications
Summary:The interaction between materials and water under many different forms – dry or wet snow, ice, frost, rime or their combination –is a complex matter to investigate, depending on many parameters, among which texturing and composition of surfaces, outside temperature, wind velocity, etc. The deposition of water, ice, etc. on structural installations, facilities and infrastructures still represents a huge problem in many cold regions whose overcoming requires innovative, less expensive and more friendly strategies. Recently, low wettable superhydrophobic surfaces gained great attention as anti-icing passive solutions able to avoid or, at least, to reduce snow, ice or frost formation and accretion at subzero temperatures. In particular, surfaces with high dynamic repellence, quantified by the Contact Angle Hysteresis (CAH), could be involved in a significant decrease of the contact time between the super-cooled liquid droplets. In this work Slippery Liquid-Infused Porous Surfaces (SLIPS) with outstanding superhydrophobic performances were obtained by deposition on aluminum alloys of hybrid nanostructured coatings characterized by the liquid nature of the smooth working interface. Commercial lubricants with different physical properties were infused on the inner inorganic layer – made up of different ceramic oxides - leading to liquid-like hybrid coatings. Contact angles against water and contact angle hysteresis (CAH) were measured by a drop shape analyzer equipped with a thermocryostat and a Peltier chamber keeping the surfaces at temperatures varying in the -2.5/-10°C range. According to the different criteria of materials’ design, the best performing surfaces showed static contact angles as high as 120°C and CAH of about 5° throughout the whole investigated range. These results allowed to select some of them as feasible candidate in view of reducing the interaction with super-cooled water drops. Chemical and structural stability of SLIPS surfaces was investigated after freezing (long-term contact with a water layer at -10±1°C) and frosting (sample placed in freezer at -10±1°C) experimental tests. A good coatings stability came out in both conditions with surfaces keeping quite unchanged their performances along a huge number of freezing/thaw cycles.