Preparation of sponge-like porous SiO2 antireflective coatings with excellent environment-resistance by an acid-catalysed sol–gel method

Silica coatings with high-transmittance and good environment-resistance properties were prepared by an acid-catalyzed sol–gel method without template. Hexamethyldisilazane (HMDS) was added into an acid-catalyzed silica sol which acted not only as the catalyst but also as a blocking agent. The effect of different contents of HMDS has been investigated. The sponge-like silica coating was obtained when the weight ratio of HMDS to SiO2 was higher than 90%. The addition of HMDS enabled these silica antireflective coatings to possess excellent hydrophobicity properties. When the weight ratio of HMDS to SiO2 was 100%, the silica coating exhibited transmittance as high as 99.64% at a given wavelength and static water contact angle of 143.0°. After 48 hours of environment aging testing at 40%, 60% and 80% RH, these coatings showed a minute decrease upon maximum transmittance, from 99.64% to 99.56%, 99.49% and 99.38%, respectively. The sponge-like HMDS-containing coatings exhibited easy-to-clean properties, which would have great potential application in laser systems.