Superhydrophobic fabrication of anodic aluminum oxide with durable and pitch-controlled nanostructure

Durable and pitch-controlled nanostructures to have well-defined superhydrophobic functions were fabricated by post-etching of AAO with a self-assembled heptadecafluoro-1,1,2,2-tetrahydrodecyl-trichlorosilane monolayer coating. The inter-pore distance at the surface of anodic aluminum oxide (AAO) was found to be an important factor for controlling the superhydrophobic adhesiveness. The hysteresis of the contact angles and the adhesiveness to a water droplet were minimized in two-steps during post-etching in phosphoric AAO (PAAO). A more durable nanostructure was obtained with the superhydrophobic surface of PAAO than those of oxalic AAO and of sulfuric AAO because of the inherent hardness of PAAO and its long inter-pore distance (500 nm).