Photoinduced Formation of Superhydrophobic Surface on Which Contact Angle of a Water Droplet Exceeds 170° by Reversible Topographical Changes on a Diarylethene Microcrystalline Surface

A superhydrophobic surface on which the contact angle of a water droplet exceeds 170 degrees was reversibly produced by alternate irradiation with UV and visible light. Superhydrophobicity is due to the formation of densely generated submicrometer sized needle-shaped crystals (less than 0.2-0.3 mu m diameter and 2.2-2.5 mu m long) at 30 degrees C, which is much lower than the eutectic temperature of either isomers of the diarylethene. Below the eutectic temperature, the generated crystals were much smaller than those generated above the eutectic temperature. These smaller crystals more effectively enhanced the superhydrophobicity.