A new method for fabricating water repellent silica films having high heat-resistance using the sol-gel method

There has been a great demand in the field of kitchen appliances to develop transparent water repellent films which have high heat-resistance around 300 degrees C. However, those films have not been obtained by conventional sol-gel methods. In this payer, we propose a new method for fabricating transparent water repellent films with high heat-resistance using the sol-gel method, in which silicon or germanium substrates were coated with a solution including tetraethoxysilane (Si(OC2H5)(4)) and (2-perfluorooctyl)ethyltrimethoxysilane (CF3(CF2)(7)C2H4Si(OCH3)(3)), followed by 'ammonia-treatment' and annealed at 300 degrees C. The contact angles of water on the ammonia-treated film maintained its initial value? 110 degrees after the heat treatment at 300 degrees C for 250 h while those on the untreated film decreased to 70 degrees, indicating that the ammonia-treatment improves heat-resistance on the film. The mechanism of ammonia-treatment was inferred from FTIR results; the ammonia-treatment should accelerate hydrolysis and polymerization of FAS and TEOS molecules, resulting in high density of siloxane bonds between FAS and silica glass. These bonds suppress the evaporation of FAS molecules from the film during the heat treatment at 300 degrees C, thus the film has high heat-resistance, (C) 1999 Elsevier Science B.V. All rights reserved.