Multivariate coupling mechanism of superhydrophobicity on NOCTUIDAE moth wing surface

Research carried out by Key Laboratory for Terrain Machine Bionics Engineering of Ministry of Education, Jilin University in Changchun, China, has shown that the co-coupling effect of scale biomaterial, micron-class shape and nanometer-class structure of vertical gibbosities of scale can induce surface hydrophobicity and self-cleaning function of the moth wing. The study is reported in Volume 54, Issue 4 (February, 2009) of Chinese Science Bulletin because of its significant research value.

The hydrophobicity, self-cleaning, anti-oxidation and pollution guarding characteristics on object surface have been found to have very wide applications to industrial, agricultural, domestic and military fields. Until now, the relationship between wetting characteristic on moth surface and scales arrangement pattern, ultrastructure and material has not been defined.

In this work, the surface shape, structure, biomaterial and wettability of moth wings (10 NOCTUIDAE species) from the northeast region of China were qualitatively and quantitatively studied. The observation shows that there are scales arranged like overlapping tiles on the surfaces of the moth wings. The shapes of the scales are different between species. They overlap horizontally and there is particular space vertically in the direction of the wing veins. The surface of the scale is structured by micron-class grooves and nanometer-class vertical gibbosities. The biomaterial components of the moth wing scale are mostly made up of protein, lipids and chitin. The observation also shows that the contact angle for wings with scales is in the range from 144.8 to 152.9, while that for those without scales is from 90.0 to 115.9. It indicates that the surfaces of the wings with scales are more hydrophobic. In addition, the equation of wettability on the NOCTUIDAE moth wing surface is established and the hydrophobic mechanism is analyzed.

This study presents that the hydrophobicity of the moth wings is induced by the multivariate coupling of the shapes, structures and biomaterials of the scales.The biomaterials are hydrophobic. And the hierarchical rough structure on moth wing surface enhances surface hydrophobicity. So the moth wing surface can not be adhered to by rainwater, dew and dust so that it keeps the flying balance, improves the flying speed and ensures flying safety. This work provides theoretical guidance to the design of perfect artificial superhydrophobic and self-cleaning materials.

The authors are affiliated to Key Laboratory for Terrain Machine Bionics Engineering of Ministry of Education. This laboratory is conducting research mainly in four respects: bionic walking of terrain machinery on soft terrain, biomimetic theory and technology on anti-adhesion and resistance reduction of terrain-machine, design on the machines to produce and process living creature and the technique of bionics, biomimetic tribology and biomimetic materials.

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