Preparation of Oleyl Phosphate-Modified TiO₂/Poly(methyl methacrylate) Hybrid Thin Films for Investigation of Their Optical Properties

TiO₂ nanoparticles (NPs) modified with oleyl phosphate were synthesized through stable Ti-O-P bonds and were utilized to prepare poly(methyl methacrylate)- (PMMA-) based hybrid thin films via the ex situ route for investigation of their optical properties. After surface modification of TiO₂ NPs with oleyl phosphate, IR and ¹³C CP/MAS NMR spectroscopy showed the presence of oleyl groups. The solid-state ³¹P MAS NMR spectrum of the product revealed that the signal due to oleyl phosphate (OP) shifted upon reaction, indicating formation of covalent Ti-O-P bonds. The modified TiO₂ NPs could be homogeneously dispersed in toluene, and the median size was 16.1 nm, which is likely to be sufficient to suppress Rayleigh scattering effectively. The TEM images of TiO₂/PMMA hybrid thin films also showed a homogeneous dispersion of TiO₂ NPs, and they exhibited excellent optical transparency even though the TiO₂ content was 20 vol%. The refractive indices of the OP-modified TiO₂/PMMA hybrid thin films changed higher with increases in TiO₂ volume fraction, and the hybrid thin film with 20 vol% of TiO₂ showed the highest refractive index (n = 1.86).