Emergence of superhydrophobic behavior on vertically aligned nanocone arrays

The authors investigate the properties of water drops on uniform arrays of vertically aligned nanocones. A simple model predicts a variety of behaviors depending on the nanocone aspect ratio. At low aspect ratios, surface tension pulls the water into the nanocone array, resulting in a wetted drop with high contact angle hysteresis. At high aspect ratios, the effect of the surface tension is reversed, resulting in little liquid-solid contact and drops which easily slide off the surface. Experiments show that the transition occurs as a gradual change in drop contact angles, but an abrupt change in sliding angles. (c) 2007 American Institute of Physics.