Preparation and Application of Superhydrophobic and Superhydrophilic Coating Films by the Sol-Gel Method

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1. Alumina thin films with roughness of 20 to SO nm were formed by the sol-gel method by immersing porous alumina gel films, which were prepared from Al(O-sec-Bu)_3 chemically modified with ethyl acetoacetate, in boiling water. The roughened surface like flower of the alumina gel films after the immersion was found to consist of boehmite crystals.2. When hydrolyzed fluoroalkyltrimethoxsilane was coated on the flower-like boehmite thin film, the contact angle for water increased with an increase of immersion time, and the immersion for 30 s was long enough to give super-water-repellency and high transparency ; the contact angle for water of the films was 165ﾟand the transmittance for the visible light was higher than 92 %.3. The super-hydrophobic alumina films coated with fluoroalkyltrimethoxysilane became super- hydrophilic after a heat treatment at temperatures higher than 500* ; the contact angle for water on the films was less than 5ﾟ.4. Fluorine-free super-hydrophobic coatings were successfully prepared on the flower-like alumina by over-coating with hydrolyzed alkyltrimethoxysilane. The length of the alkyl groups and the concentration of the alkyltrimethoxysilane in the coating solution affected the hydrophobicity of the resultant coating films.5. We have prepared super-hydrophobic coatings without flower-like alumina under layer using several organoalkoxysilanes. Among the organoalkoxysilanes examined, dimethyldiethoxysilane and phenyltriethoxysilane formed transparent super-hydrophobic coatings by heat-treating their films. SEM observation showed that the coating had a finely roughened surface with fractal structure.