Formation of superhydrophobic-superhydrophilic pattern on flowerlike alumina thin film by the sol-gel method

We have prepared superhydrophobic surfaces which become superhydrophilic by heat-treatment at 500 degreesC or irradiation of UV-light. When hydrolyzed fluoroalkyltrimethoxysilane (FAS) was coated on Al2O3 gel film with a roughness of 20 to 50 nm, the films showed superhydrophobicity and high transparency; the contact angle for water of the film was 165 degrees and the transmittance for the visible light was higher than 92%. When the FAS-coated thin films were heat-treated at temperatures higher than 500 degreesC, the films became superhydrophilic; the contact angle for water on the films was smaller than 5 degrees. Thin films of amorphous TiO2 or anatase TiO2 were coated between Al2O3 gel and FAS layer, and the contact angle for water was also about 160 degrees. UV irradiation using high-pressure mercury lamp on these films resulted in the contact angle to be smaller than 5 degrees. When UV light was irradiated through a photomask, superhydrophobic-superhydrophilic micropatterns applicable as a stamper for printing or a substrate of micro-optical components were successfully obtained on the films.