Ice resistance of hydrophobic fluoropolymerized nanostructured alumina films for antireflective coatings

The functionality and durability of nanostructured alumina coatings exposed to atmospheric icing has been assessed to probe their usability in practical applications and to estimate the need for further development of the coatings. In particular, the changes in surface microstructure and in optical performance as well as in the wetting characteristics of the surfaces are reported. Without a hydrophobicity treatment the alumina nanostructures are superhydrophilic and do not endure large environmental changes. Hydrophobicity treated fluoropolymerized nanostructured alumina provides characteristics with partial anti-icing capabilities, enhanced durability, and excellent transmission levels of >95%, but the performance degrades in cyclic icing/de-icing. However, the hydrophobic nanostructured alumina outperforms both the nanostructured and planar alumina coatings and possesses increased durability and stability even under harsh conditions, such as the atmospheric icing. This indicates a clear need to use a hydrophobicity treatment for the nanostructured alumina antireflection coatings to be used in any environments. Therefore, its utilization in applications where little or occasional exposure to icing or other humidity and temperature changes is favorable over standard planar coatings. Further process optimization of the hydrophobicity treatment is still needed for better durability for cyclical icing exposure.