LAUSR

Abstract Nature has always provided a lot of inspirations for engineers and scientists. The butterfly wing is a kind of typical surface that performs excellent properties of superhydrophobicity especially for the front side of the wings. However, in this work, it was interestingly found that the back side of butterfly Papilio ulysses wings exhibits a better long-term durability of superhydrophobic properties under water than the front side of the wing. In the process of the experiment, both sides of butterfly wings were soaked under the deionized water within 60 h and measured the changes of the contact angle (CA) at regular intervals. It was discovered that the back side of butterfly Papilio ulysses wings shows stronger hydrophobicity under continuous contact with water. In contrast, the front side of the wings was obviously somewhat “poorly” in the aspect of superhydrophobicity after a long soak underwater. Then, the optimized 3D configurations of the coupling structures were determined by using the Field Emission Scanning Electron Microscope ( FESEM ). It was found that there are so much little hairs on and between the scales on the back side, which don’t existed on the front side of the wings. At last, the underwater superhydrophobic mechanism of the back side of butterfly wing scales was revealed. In fact, the strong superhydrophobicity underwater of the back side of butterfly wings should be owing to its special surface structures. The hairs between scales on back side of butterfly wings could prevent the liquid from moving down rapidly underwater. When it reached the new balance, the forces will form the second balance and the liquid level advanced slowly very much. So, the back side of butterfly wing exhibits a better long-term durability of superhydrophobic properties under water than the front side of the wings. If this functional “biomimetic structure” could be applied on metal surface, it would be potential not only to the passive drag reduction but also to preventing bacteria from adhesion to the ships or other aquatic vessels.