TRANSPARENT TiO2-PMMA NANOHYBRIDS OF HIGH NANOCRYSTALLINITY AND ENHANCED NONLINEAR OPTICAL PROPERTIES

Abstract

Nanohybrid thin films of titania-polymethyl methacrylate ( TiO2 -PMMA) with varying degrees of nanocrystallinity have been successfully synthesized via an in-situ sol gel-polymerization route, assisted by subsequent thermal and water vapor treatments. Post-hydrothermal treatment by water vapor at relatively low temperatures led to a higher degree of crystallinity for TiO2 nanoparticles than the conventional thermal annealing. The degree of TiO2 crystallinity in the resulting nanohybrid films was studied by using XRD, FTIR, UV-Vis spectroscopies and HRTEM. The resulting nanohybrid thin films are highly transparent in the visible region, with an estimated band gap energies, Eg, close to that of anatase TiO2 (~ 3.20 eV). The nanocrystallinity level of TiO2 phase strongly affects both linear and nonlinear optical properties of the nanohybrids. A significant enhancement in linear refractive index, no, up to 1.780 and a third-order nonlinear optical susceptibility, χ(3) as high as 5.27 × 10-9 esu , were demonstrated with the nanohybrid exhibiting the enhanced TiO2 crystallinity and well-preserved PMMA matrix.