Preparation of hydrophobic SiO2/PMHS sol and ORMOSIL antireflective films for solar glass cover

Abstract

Adjusting the porosity of films to obtain a suitable refractive index is one of the key technical concerns of the porous silica antireflective coatings (ARCs) preparation via sol–gel process. However, it is challenging to reduce the refractive index below than 1.20 with the conventional process. In the meantime, residual silanol groups (Si–OH) on coated glasses may deteriorate the weatherability of the ARCs. In this paper, a novel organically modified silicate (ORMOSL) ARCs with good hydrophobicity property and variable refractive index from 1.18 to 1.36 were prepared by modifying the silica sol with polymethylhydrosiloxane (PMHS). In the reaction with PMHS, silica micelle was cross-linked and regrew to synthesize partly clustered ORMOSIL micelle. The ORMOSIL micelles were coated on the soda-lime glasses to form monolayer ARCs. The antireflection and hydrophobicity properties of the coated glasses were significantly improved, i.e., optical transmittance up to 7% gain in the visible range with 130° water contact angle was obtained. Satisfyingly, the SiO2–PMHS sol showed excellent stability with a shelf life of up to 40–105days. In addition, the structure and morphology of the ORMOSIL films were investigated and “Cross-link and fill” model was proposed to explain the effect of PMHS content on the properties of sols and ARCs.