Abstract: The wetting behaviors of methanol/water solution on butterfly wing surface were investigated using a video-based contact angle meter and a scanning electron microscope, and the mechanism of wetting by methanol on butterfly wing surface was discussed by Cassie model. The butterfly wing surfaces display high hydrophobicity (contact angles of distilled water 134.0°～159.2°) and resistant ability against wetting by methanol solution (contact angles of 45% methanol solution 91.3°～128.5°). On wing surfaces of 32 butterfly species tested, the critical concentrations for wetting and spreadingwetting of methanol solution are 50% and 70%, respectively. On wing surface of Polygonia c-aureum, when methanol concentration is lower than 45%, the body force of a droplet is bigger than the surface force on nanometer-structures, liquid fills up the nanometer- grooves; while the body force on micrometer-structures is smaller than the surface force, droplets are upheld by micrometer-structures, wetting does not occur on the wing surface. When 45%≤methanol concentration<65%, the body force of a droplet is bigger than the surface force on both nanometer- and micrometer-structures, droplets collapse. When methanol concentration is increased to 65%, the wing surfaces are wetted, composite contact is transferred to wet contact.

Key words: engineering bionics, butterfly, wettability, methanol, micro-/nano-structure, air fraction