High performance double layer hydrophobic antireflective coatings on glass prepared by sol-gel method

A double layer coating was designed and fabricated on glass surfaces by sol-gel method using a silica-titania (SiO2-TiO2) thin film as the bottom layer and an inorganic-organic (triethoxy(octyl)silane (OTES) modified SiO2) upper layer. SiO2 and TiO2 sols were prepared using tetraethyl orthosilicate (TEOS) and titanium isopropoxide (TIP) as precursors and nitric acid (HNO3) as catalyst. The refractive index of the SiO2-TiO2 and OTES modified SiO2 layers were 1.79 and 1.45, and their thicknesses were approximately 76.8 nm and 94.2 nm, respectively. The results show an increase of 7% in transmittance respect to the uncoated glass substrate. At the same time, OTES-modified SiO2 top layer significantly improved the hydrophobicity of the system; the water contact angle of film increased from 56 degrees for system without the OTES modified SiO2 layer to 102 degrees for the system with OTES-modified SiO2 top layer.