Sol–gel preparation of fluoro-containing ORMOSIL antireflective coating with resistance simultaneously to hydrophilic and oleophilic pollutants

Abstract

Fluoro-containing ORMOSIL (organically modified silicate) sols were prepared by a one-pot sol–gel Stober route by co-condensation of tetraethylorthosilicate (TEOS) and fluorinated alkyl silane [1H, 1H, 2H, 2H-perfluorodecyltriethoxysilanes, (POTS)] using isopropanol as dispersant and ammonia as catalyst. Antireflective (AR) coatings from these sols were prepared by dip coating. It was found that isopropanol not only played as dispersant but also grafted to the surface of colloidal silica particles, and therefore gave the fluoro-free AR coating an almost superhydrophobic property. By increasing the molar ratio of POTS to TEOS, the oleophobicity of AR coatings increased gradually. As the molar ratio of POTS to TEOS is 0.05, the AR coating had the advantages of excellent hydrophobicity, improved oleophobicity and high transmittance. The water, CH2I2 and polydimethyl siloxane contact angles are 143°, 119° and 85°, respectively. The water contact angle was further increased to be higher than 150° by a further surface hydrophobic modification with hexamethylisilazane. The coated glass substrates (BK-7) had very high transmittance of up to 99.8 % at a determined wavelength and had good AR stability to the hydrophilic and oleophilic pollutants. By exposing to humid environment (about 95 % humidity) for 2 months, the transmittance of fluoro-free AR coating decreased from 99.9 to about 99.5 % while that of superhydrphobic and oleophobic AR coating decreased from 99.8 to 99.6 %. Being placed in a vacuum chamber which had organic pollutants volatilized from vacuum pump oil, the transmittance of fluoro-free silica AR coating decreased seriously from 99.9 to 97.8 % while that of fluoro-containing ORMOSIL AR coating decreased slightly from 99.8 to 99.1 %. Fluoro-containing ORMOSIL antireflective coating with resistance simultaneously to hydrophilic and oleophilic pollutants was prepared by sol–gel process.