Unique Hydrophobization and Hybridization via Direct Phase Transfer of ZrO2 Nanoparticles from Water to Toluene Producing Highly Transparent Polystyrene and Poly(methyl methacrylate) Hybrid Bulk Materials

A versatile and promising organic–inorganic hybridization method is proposed for the fabrication of highly transparent polystyrene (PSt) and poly(methyl methacrylate) (PMMA) hybrid bulk materials containing highly crystalline ZrO 2 nanoparticles (NPs) having a number-average diameter of 3.11 nm. The two key technologies that have been developed are the surface treatment, hydrophobization, and functionalization of ZrO 2 NPs originally dispersed in water and their nanodispersion into a polymer continuous phase without any coagulation and/or agglomeration. A unique and fascinating surface treatment method is demonstrated in which the hydrophobization and phase transfer of ZrO 2 NPs from water to toluene is simultaneously achieved. Transparent surface-modified ZrO 2 nanodispersions in toluene are obtained by a gentle solvent exchange from a ternary solvent mixture composed of water, toluene, and methanol. The addition of carboxylic acids having more than four carbon atoms as the surface treatment agent enables this hydrophobization. The carboxylic acid-modified ZrO 2 NPs prepared by the method are thoroughly characterized by small-angle X-ray scattering (SAXS), dynamic light scattering (DLS), scanning TEM, TGA, and NMR, and IR spectroscopies. The surface-treated ZrO 2 NP powders after drying possess the ability of redissolution or nanodispersion in several organic solvents and vinyl monomers. Further, optically transparent PSt and PMMA hybrid bulk materials with thicknesses of 10 mm are fabricated by the copolymerization of styrene (St) or methyl methacrylate (MMA) as a representative vinylic monomer with methacrylate-functionalized ZrO 2 NPs as the multivinyl cross-linking agent. The optical properties of hybrid materials having a higher refractive index than that of the original homopolymers are measured and compared with the theories based on Fresnel refraction, Lorentz–Lorenz effective medium expansion, and Lambert–Beer and Rayleigh scattering equations. The present method provides promising candidates for different transparent hybrid materials consisting of inorganic and organic materials.