Studies of the anisotropic property when water droplet moves on butterfly wings

The morphology of the butterfly wings(Morpho Achilles) surface was observed by scanning electron microscope(SEM) and the wettability was characterized by the apparent contact angle. The adhesive forces between the water droplets and the surface of butterfly wings under different direction were characterized by a high-sensitivity microelectromechanical balance system. The experimental results show that the adhesive force when the water droplet moved along the direction of stacked scales was obviously smaller and more stable than that of other directions. If the wings were wetted, the adhesive forces were similar no matter in which direction the water droplets moved; the force along the direction of stacked scales even would be bigger than that against the direction of stacked scales.