Structural, optical, and electrical properties of Bi2O3/MWCNT-doped PVA/NaAlg Nanocomposite films for flexible Electronic applications

Nanocomposite films comprising a polyvinyl alcohol (PVA) and sodium alginate (NaAlg) polymer blend doped with Bi₂O₃/multi-walled carbon nanotube (MWCNT) hybrid nanostructures were prepared via the solution casting method. The Bi₂O₃/MWCNT fillers, synthesized using the sol–gel technique, were incorporated into the polymer matrix at concentrations of 0, 4, 6, 8, and 12 wt%. X-ray diffraction (XRD) analysis revealed a progressive reduction in the degree of crystallinity from 55.78 % in the pristine blend to 31.28 % at 12 wt% filler loading, indicating an increase in amorphous content. Fourier-transform infrared (FT-IR) spectroscopy confirmed strong interfacial interactions between the hybrid nanofillers and the functional groups of PVA/NaAlg, suggesting the formation of charge transfer complexes. Optical absorption measurements showed that the absorption intensity increased while the optical bandgap decreased from 3.33 eV (0 wt%) to 2.89 eV (12 wt%) for the indirect transition, enhancing the material's light-harvesting efficiency. Electrical studies demonstrated that the AC conductivity increased from approximately 1.73 × 10⁻¹² S/cm for the pristine PVA/NaAlg blend to 1.39 × 10⁻⁷ at 12 wt% Bi₂O₃/MWCNT. This improvement was accompanied by an increase in the dielectric constant, attributed to enhanced charge carrier mobility and interfacial polarization. Electric modulus and Argand plot analyses revealed non-Debye relaxation behavior and higher ionic conductivity with increasing Bi₂O₃/MWCNT content. These results demonstrate that Bi₂O₃/MWCNT-doped PVA/NaAlg nanocomposites exhibit excellent structural tunability and multifunctional performance, making them promising candidates for next-generation flexible electronic and optoelectronic devices.