Multilevel Micronanoscale Texture Effects on Fly Wing Membrane–Water Droplet Interaction

The wettable surface or nonwettable surface that is derived from a multilevel micronanoscale structure is abundant in nature and biomimetic commodities. Those hoverflies with the seta-coated wing membrane detached from impacting free-falling raindrops were observed in static states. A hoverfly wing membrane with well-ordered setae was identified as a robust nonwettable surface, and the static water contact angle θ on the wing membrane at the microscopic scale is 136.84 ± 0.98°. Hoverfly wing membrane–water droplet interaction with the actual truth and the theoretical models was discussed and indicated that the theoretical calculation might not state the actual situation, arising from the membrane or seta–drop–bubble interaction and those multilevel micronanoscale structure characteristics on the wing membrane. Detailed investigation on nonwettable surface–wettable surface transformation with surface CaCO₃ accumulation in a carbonization reaction and the characteristic transformation toward the hoverfly wing membrane with the multilevel micronanoscale structure was carried out. Then, the CaCO₃ accumulation on PDMS texture films was carried out and the static water contact angle θ was tested. Those observations offer ideas to fabricate artificial films with a multilevel micronanoscale structure that could obtain some characteristics, i.e., nonwettable surface–wettable surface transformation.