Directional adhesion of superhydrophobic butterfly wings

We showed directional adhesion on the superhydrophobic wings of the butterfly . A droplet easily rolls off the surface of the wings along the radial outward (RO) direction of the central axis of the body, but is pinned tightly against the RO direction. Interestingly, these two distinct states can be tuned by controlling the posture of the wings (downward or upward) and the direction of airflow across the surface (along or against the RO direction), respectively. Research indicated that these special abilities resulted from the direction-dependent arrangement of nano-tips on ridging nano-stripes and micro-scales overlapped on the wings at the level, where two distinct contact modes of a droplet with…