Impact of doping different concentrations of TiO2 nanoparticles to PMMA on its structural, thermal and optical properties for optical applications

The aim of the present work is to analyze the macrostructure, thermal and optical properties of nanocomposite films prepared from poly(methyl methacrylate) doped with titanium dioxide using solution casting process for optoelectronic applications. The films were examined using Fourier transform infrared (FTIR) spectroscopy, which showed that the addition of TiO₂NPs completely disperses into the PMMA matrix and causes significant changes in the width, intensity and positions of PMMA vibration peaks. Differential thermal analysis (DTA) and thermogravimetric analysis (TGA/DTGA) were used to study the thermal stability of the synthesized nanocomposite films. The melting point, area and shape of the thermal peaks in the DTA results varied, indicating different levels of crystallinity. According to TGA analysis, the nanocomposites decomposed in three stages and were thermally stable. The optical transmittance, absorption and reflectance spectra of the films were measured in the visible region. As the concentration of TiO₂NPs increased to 8 wt %, the results showed that the transmittance decreases and the absorption increases, reaching the maximum opacity (≈27 %). The linear optical parameters showed that the absorption coefficient, extinction coefficient, refractive index, dielectric constants, and optical conductivity increased with the increase of TiO₂NPs incorporated into PMMA matrix. The Urbach energy values ​​increased from 0.220 to 0.247 eV (≈12 %), while a slight decrease in the direct band gap values ​​from 2.910 to 2.899 eV and the indirect band gap from 2.615 to 2.568 eV was found after the incorporation of TiO₂NPs, indicating the presence of a structural defect in the PMMA matrix. Using the Wemple-DiDomenico model, the linear dispersion parameters, linear optical susceptibility and nonlinear optical properties such as third nonlinear optical susceptibility and nonlinear refractive index were calculated and found to be functions of the TiO₂NPs concentration. The results indicate that the prepared nanocomposite films can be considered as a promising candidate for use in optoelectronic applications.