Tunable wettability in surface-modified ZnO-based hierarchical nanostructures

Designing geometrical structures and making chemical modifications are two effective routes to tailor wettability. ZnO-based hierarchical nanostructures, in particular, vertically aligned nanoneedles and nanonails were employed as a platform to study the effect of surface morphology. The hydrophobicity and the variation of contact angle in the as-grown samples were attributed to the combined effects of surface roughness and partial water-solid contact. Subsequent chemical modifications with stearic acid led to superhydrophobic ZnO surfaces, while annealing in air resulted into superhydrophilicity. Under the alternations of coating and removal of stearic acid, reversible transitions between superhydrophilicity and hydrophobicity were realized.