Superhydrophobic zinc oxide surface by differential etching and hydrophobic modification

A superhydrophobic ZnO nanorod films on zinc substrate were fabricated by natural oxidation of zinc metal and subsequent modification with a monolayer of n-octadecyl thiol (ODT). The surface morphology and composition were studied using SEM, XRD, and XPS, respectively. The surface of ZnO films directly grown on zinc substrate was hydrophilic with a water contact angle (CA) of 40 ± 2°, whereas the modified ZnO films by ODT exhibited the superhydrophobicity and the water CA on it was 153 ± 2°. It is shown that both the higher surface roughness and the lower surface free energy play an important role in creating the superhydrophobic surface.