Condensed-drop repellency of butterfly wings with biological photonic crystals

We use the environmental scanning electronic microscopy(ESEM) to observe the micro-/nanostructure of Morpho nestira butterfly wing, and reveal the anisotropic structure feature in conjunction with iridescent structural color of butterfly wing. We observe the dynamic characteristics of water condensation and wettability on butterfly wing by the high-speed camera, and discuss the water repellency on butterfly wing under different tilt-degree and vibration conditions. It is found that a robust water repellency property appears on Morpho nestira butterfly wing. The dynamic contact angle experiment is used to examine the contact angle hysteresis by measuring the advancing angle and receding angle, the low adhesion property in conjunction with contact angle hysteresis can be demonstrated by the difference of receding angle and receding angle. The result reveals that the robust water repellency on Morpho nestira butterfly wing is attributed to the effect of micro- and nano-structure on butterfly wing. Furthermore, we elucidate the mechanism of special wettability and repellency of water condensation based on micro-/nano-structures of butterfly wing.