Refractive index modulation in PS/TiO2 polymer nanocomposites via nanoparticle Dimension control

The effect of titanium dioxide (TiO 2 ) nanoparticle size on the refractive index (RI) of polystyrene (PS), one of the most important physicochemical parameters of polymer materials, was investigated. TiO 2 nanoparticles (NPs) of three distinct sizes, approximately 5 nm, 10 nm, and 14 nm, were synthesized via a controlled hydrothermal method by varying the precursor composition, solvent ratio, surfactants and reaction conditions, incorporated into polystyrene matrix at different concentrations, and subsequently fabricated into thin films via spin coating. The effect of particle size, filler loading and UV-curing was systematically investigated. An ∼ 18% increase in the refractive index was observed for UV-cured composites containing large-sized, high-loading TiO 2 , accompanied by moderate transparency loss. Surface modification could improve nanoparticle dispersion and interfacial adhesion, reduce light scattering and enhance optical homogeneity. The experimental refractive index was further analyzed theoretically using the linear mixing rule (Agro-Biot rule) and extended Lorentz-Lorenz (L-L) equations.