Role of surface roughness on wettability and coefficient of restitution in butterfly wings

Abstract

Surface nano-structure and roughness play a vital role in controlling the wettability and bouncing of water drops on wings of butterfly/moth species. A detailed experimental study was conducted to investigate the effect of nano-structure on static and dynamic contact angle measurements and coefficient of restitution of four different butterfly wing surfaces. Surface characterization at different length scales was performed using atomic force microscopy (AFM), optical profilometry and scanning electron microscopy. The water drop bouncing experiments were conducted on the surface of butterfly wings to investigate the coefficient of restitution. Contact angle measurements reveal that the wings which had high roughness factors resulted high static and dynamic (advancing and receding) contact angles with the exception of Antheraea Polyphemus. The wings that had a combination of scales and hair like microtrichia structure showed increased roughness and hydrophobicity compared to wings that had only either one of them.