Impact dynamics and rebound of water droplets on superhydrophobic carbon nanotube arrays

The authors report the impact response of water droplets impinging on superhydrophobic carbon nanotube arrays and observe that arrays with different wetting properties display significantly different responses. For an array with a static contact angle of 163 degrees, the droplet bounces off the surface several times, while for an array with a reduced contact angle of 140 degrees, the droplet does not rebound and remains pinned. The contact angle hysteresis and contact line pinning for the 140 degrees array suggest that the momentum of the droplet during the initial impact enables it to penetrate and displace the air pockets that are responsible for the superhydrophobicity of the array under static conditions. (C) 2007 American Institute of Physics.