Effect of $\hbox {WO}_{3}$ nanoparticle doping on the physical properties of PVC polymer

Abstract

Poly(vinyl chloride)/tungsten oxide ($\hbox {PVC}/\hbox {WO}_{3})$ nanocomposite films were synthesized with different ratio of $\hbox {WO}_{3}$ content (0, 0.05, 0.1, 0.2 and 0.3 wt%). The sol–gel method was used to prepare $\hbox {WO}_{3}$ nanoparticles (NPs). X-ray diffraction and scanning electron microscope techniques confirmed that the $\hbox {WO}_{3}$ NPs were successfully dispersed in a PVC matrix with a single-phase structure. Characteristic absorption bands were observed in infrared spectra for pure PVC and nanocomposites. The morphology of $\hbox {WO}_{3}$ was observed using transmission electron microscope. The optical energy band gaps ($E_{\mathrm{opt}}$; direct and indirect) were estimated by using Tauc’s formula. It was found that the direct band gap energies decreased from 5.15 to 4.53 eV and the indirect bands decreased from 4.8 to 4.1 eV as $\hbox {WO}_{3}$ doping increased, while the Urbach energy ($E_{\mathrm{u}}$) increased as $\hbox {WO}_{3}$ content increased. It was found that the steepness parameter decreased, which confirms the formation of localized states in the band gap and increasing disorder in PVC polymer samples. The dielectric constant ($\varepsilon '$) of the $\hbox {PVC}/\hbox {WO}_{3}$ nanocomposite films decreased as frequency increased. At a low frequency region, the loss factor ($\varepsilon ''$) has a high value and then sharply decreased as frequency increased, reaching a frequency independent region at high frequency values. The obtained data are very useful for using the investigated samples ($\hbox {PVC}/\hbox {WO}_{3}$) as the cores of high frequency transformers with very low dielectric loss.