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 3 00 degrees C. However, those films have not been obtained by conventional s ol-gel methods. In this payer, we propose a new method for fabricating tran sparent water repellent films with high heat-resistance using the sol-gel m ethod, in which silicon or germanium substrates were coated with a solution including tetraethoxysilane (Si(OC2H5)(4)) and (2-perfluorooctyl)ethyltrim ethoxysilane (CF3(CF2)(7)C2H4Si(OCH3)(3)), followed by 'ammonia-treatment' and annealed at 300 degrees C. The contact angles of water on the ammonia-t reated film maintained its initial value? 110 degrees after the heat treatm ent at 300 degrees C for 250 h while those on the untreated film decreased to 70 degrees, indicating that the ammonia-treatment improves heat-resistan ce on the film. The mechanism of ammonia-treatment was inferred from FTIR r esults; the ammonia-treatment should accelerate hydrolysis and polymerizati on of FAS and TEOS molecules, resulting in high density of siloxane bonds b etween FAS and silica glass. These bonds suppress the evaporation of FAS mo lecules 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 re served.