Effects of methanol on wettability of the non-smooth surface on butterfly wing

The contact angles of distilled water and methanol solution on the wings of butterflies were determined by a visual contact angle measuring system. The scale structures of the wings were observed using scanning electron microscopy, The influence of the scale micro- and ultra-structure on the wettability was investigated. Results show that the contact angle of distilled water on the wing surfaces varies from 134.0 degrees to 159.2 degrees. High hydrophobicity is found in six species with contact angles greater than 150 degrees. The wing surfaces of some species are not only hydrophobic but also resist the wetting by methanol solution with 55% concentration. Only two species in Parnassius can not resist the wetting because the micro-structure (spindle-like shape) and ultra-structure (pinnule-like shape) of the wing scales are remarkably different from that of other species. The concentration of methanol solution for the occurrence of spreading/wetting on the wing surfaces of different species varies from 70% to 9:5%. After wetting by methanol solution for 10 min, the distilled water contact angle on the wing surface increases by 0.8 degrees-2.1 degrees, showing the promotion of capacity against wetting by distilled water.