Hard coatings for CR-39 based on Al2O3-ZrO2 3-glycidoxypropyltrimethoxysilane (GPTMS) and tetraethoxysilane (TEOS) nanocomposites

The optical and mechanical properties of single layer nanocomposite films, with refractive indices (n) matched for an allyl diglycol carbonate (CR-39) substrate, with n = 1.50, were investigated. Alumina nanoparticles (ALO NPs 20 nm) and zirconia nanoparticles (ZrAc NPs 50 nm) in colloidal form were incorporated in the nanocomposites to improve film strength and control the refractive index. The coating solution was prepared from hydrolysis between tetraethoxysilane (TEOS) and 3-glycidoxypropyl trimethoxysilane (GPTMS) in the presence of colloidal nanoparticles. GPTMS functioned as a matrix for the nanocomposite film and promoted adhesion between the film and substrate. Meanwhile, TEOS, a four-armed crosslink network, provided internal structural strength through network formation. The optimum ratio of GPTMS:TEOS:NPs was at 28:12:24 by weight percent (wt%). The nanocomposite film with 24 wt% of ZrAc yielded a harder film with a slightly higher refractive index (n = 1.53 at 550 nm) than the CR-39 substrate (n = 1.51 at 550 nm). The film with 24 wt% of ALO showed a refractive index close to that of CR-39, but possessed poorer scratch resistance. The coating film at 12:12 wt% of ALO:ZrAc provided a refractive index suitable for the CR-39 substrate. The film also showed good scratch resistance, good adhesion, and excellent optical properties.