Morphological, structural, dielectric and electrical properties of PEO-ZnO nanodielectric films

The morphological, structural, dielectric and electrical properties of aqueous solution-cast prepared poly(ethylene oxide)-zinc oxide (PEO-ZnO) nanocomposite films have been investigated as a function of ZnO nanoparticle concentrations up to 5 wt%. Scanning electron microscopy (SEM) images of these films show that the morphology of pristine PEO aggregated spherulites changes into fluffy, voluminous and highly porous with dispersion of ZnO nanoparticles into the PEO matrix. X-ray diffraction (XRD) study confirms that the crystalline phase of PEO greatly reduces at 1 wt% ZnO, and it again increases gradually with further increase of ZnO concentration. The dielectric relaxation spectroscopy (DRS) over the frequency range 20 Hz-1 MHz reveals that the real part of complex dielectric permittivity at audio frequencies decreases non-linearly whereas it remains almost constant at radio frequencies for these polymeric nanocomposites. Dispersion of nanosize ZnO particles into the PEO matrix reduces the values of dielectric permittivity which also exhibits a correlation with the dispersivity of ZnO nanoparticles. The relaxation peaks observed in the dielectric loss tangent and electric modulus spectra reveal that the electrostatic interactions of nanoscale ZnO particles with the ethylene oxide functional dipolar group of PEO monomer units decrease the local chain segmental dynamics of the polymer. Real part of ac conductivity spectra of these films have been analyzed by power law fit over the audio and radio frequency regions, respectively, and the obtained dc conductivity values for these regions differ by more than two orders of magnitude. The temperature dependent relaxation time and dc conductivity values of the nanodielectric material obey the Arrhenius relation of activation energies and confirm a correlation between dc conductivity and PEO chain segmental motion which is exactly identical to the characteristics of solid polymer electrolytes. Results imply that these nanocomposite materials can serve as low permittivity flexible nanodielectric for radio frequency microelectronic devices and also as electrical insulator for audio frequency operating conventional devices in addition to their suitability in preparation of solid polymer electrolytes.