Strelitzia reginae leaf as a natural template for anisotropic wetting and superhydrophobicity

Artificial surfaces that exhibit unidirectional water spreading and superhydrophobicity are obtained by Strelitzia reginae leaves. Both green and dried leaves are used, thus exploiting the plant senescence. We demonstrate that the natural drying process of the leaves strongly affects the surface morphology and wettability. Polymeric stamps from the green leaf show an arrangement of periodic microridges/microgrooves that favor anisotropic wetting, with a water contact angle (WCA) variation of about 21% along the two principal directions. Instead, the shrinkage of the leaf tissue, as a consequence of the natural dehydration process, induces an enhancement of the superficial corrugation. This results in the establishment of a superhydrophobic state, which shows a WCA of up to 160°, and water rolling off. S. reginae leaves are therefore easily accessible stamps suitable for controlling wettability and realizing surfaces that exhibit various wetting behaviors.