The superhydrophobic properties of self-organized microstructured surfaces derived from anodically oxidized Al/Nb and Al/Ta metal layers

Al/Nb (aluminium-on-niobium) and Al/Ta (aluminium-on-tantalum) metal layers sputter-deposited onto Si wafers were anodized respectively in 0.06 and 0.1 mol dm(-3) citric acid electrolytes under a high voltage of 480 and 400V in order to consecutively grow porous alumina layers with the longest interpore distances, this followed by growth of self-organized arrays of micro-sized goblets-like niobium oxide structures and eryngii-mushrooms-like tantalum oxide structures protruding through the alumina barrier layer. The shape and size of the metal oxide microstructures were additionally tailored by post-anodizing treatment combining partial open-circuit dissolution of the alumina pores with reanodizing the underlying metal through the as grown and expanded pores. The structured metal oxide surfaces derived after selectively dissolving away the anodic alumina layers were coated with fluoroalkyl phosphate (FAP) and tested for their non-wetting properties by measuring static contact angles for water droplets. Both the FAP-coated goblet and eryngii-mushroom surfaces showed superhydrophobic behaviour with the contact angles of 158 and 156 respectively. The effect is due to the creation of composite solid-liquid-air interfaces that allow for dramatically decreased liquid-to-solid contact area and adhesion, in accord with the Cassie-Baxter model. (c) 2012 Elsevier Ltd. All rights reserved.