Photoresponsive superhydrophobic surfaces for effective wetting control.

Dynamically tuning the surface wettability has long been a scientific challenge, but of great importance in surface science. Robust superhydrophobic surfaces, displaying switchable and tunable extreme wetting behaviors, are successfully developed by spraying photoresponsive hydrophobic nanoparticles onto various substrates. The surface wettability can be intelligently adjusted by applying irradiation with UV or visible light, which is assumed to initiate large conformation changes of azobenzene units at the coating surface, resulting in distinct surface energy change and thus controlled wetting behaviors. The underlying wetting mechanism about the resulting surfaces is systematically investigated and supported by the estimation of water contact angles using newly rewritten Cassie-Baxter and Wenzel relations and also by the evaluation of solid surface free energy adopting the Owens-Wendt approach. The methodology proposed may provide a novel way of tuning surface wettability and investigating the wetting transition mechanism and also promote applications in self-cleaning and smart fluid control.