Wetting properties on nanostructured surfaces of cicada wings.

This study has investigated the wettability of forewings of 15 species of cicadas, with distinctly different wetting properties related to their nanostructures. The wing surfaces exhibited hydrophilic or weak to strong hydrophobic properties with contact angles ranging from 76.8 deg. to 146.0 deg. The nanostructures (protrusions), observed using environmental scanning electron microscopy (ESEM), were classified into four types according to the patterning, diameter (82-148 nm), spacing (44-117 nm) and height (159-446 nm). Surface analysis by X-ray photoelectron spectroscopy (XPS) showed significant differences in wing membrane chemistry. Thus, wetting properties at the macroscopic scale were dependent on slight differences in nanoscale architecture and composition of the wax layer. This investigation offers insights into the diversity of nanostructuring and how subtle small-scale changes may facilitate large changes in wettability.