UV resistance of sol-gel hydrophobic silica antireflective coatings

Abstract

Hydrophobic surface with satisfactory resistance to ultraviolet (UV) radiation plays a vital role in sol–gel porous antireflective (AR) coatings. In this work, sol–gel hydrophobic silica AR coatings were prepared by modifying the surface of nanoparticles with fluorine-free organosilanes (hexamethyldisilazane, hexadecyltrimethoxysilane, and N-octyltrimethoxysilane) or fluorine-containing silanes (1H, 1H, 2H, 2H-perfluoroalkyltriethoxysilane and 1H, 1H, 2H, 2H-perfluorooctyltrichlorosilane). The UV resistance of the coatings grafted with different hydrophobic groups was studied through monitoring the changes in wettability and optical properties of the coatings before and after UV irradiation. In addition, the evolution in the surface characteristics of the coatings after UV irradiation was evaluated by studying their surface morphology and chemical composition. Based on the contact angle results, the surface free energy (SFE) of the coatings before and after UV irradiation was estimated and compared. After UV irradiation, the SFE of fluorine-free organosilane-modified silica coatings increases dramatically, whereas the coatings modified with the fluoroalkyl silanes still maintain very low SFE. The high bond energy of C−F provides a particularly high degree of resistance to UV light damage, which imparts the long-chain fluoroalkyl-grafted POTS/SiO2 and POTCS/SiO2 coatings with superior UV resistance. The fluorine-containing organosilane modification provides an effective way to simultaneously integrate high transparency and excellent UV resistance for hydrophobic silica coatings. [Figure not available: see fulltext.].