Cicada wing-inspired artificial nanopatterns with antifouling properties for clay adhesion

To clarify the antifouling properties of cicada-inspired nanostructured surfaces and search for a long-term usable antifouling material, the wings of two types of cicadas in Japan, Graptopsaltria nigrofuscata (GN) and Cryptotympana facialis (CF), were examined by surface wettability and surface free energy. Furthermore, considering the complexity and mechanical stability of natural nanostructured surfaces, we mimicked both cicada wing surfaces by combining nanosphere lithography and metal-assisted chemical etching (MacEtch) on Si wafer, which is low-cost and large-area pattern-fabricable. We obtained artificial nanopatterns with pillar pitches of 200, 500, and 1000 nm (naming 200, 500, and 1000 series). As a result, comparing artificial nanopatterns with cicada wings indicated that nanopillar structures with high roughness factors or structural aspect ratios are likely to have excellent hydrophobic properties and antifouling features. Cryptotympana facialis wings and 200 series Si samples showed less clay particle adhesion than other patterns. These results indicate smaller structured surfaces where air may get trapped, resulting in hydrophobic surfaces contributing to self-cleaning or fouling-release properties. Further, reducing the contact area between nanostructures and clay can be used as an effective strategy to prevent clay adhesion has been proposed, but it has targeted limitations. Herein, we present a novel insight that more fine and high-structural-density nanostructural patterns are universal to prevent clay adhesion.