Structural,thermal, and electrical studies of sodium iodide (NaI)-doped hydroxypropyl methylcellulose (HPMC) polymer electrolyte films

Solid polymer electrolyte films based on hydroxypropyl methylcellulose (HPMC) complexed with sodium iodide (NaI) were prepared using solution cast method. The dissolution of the salt into the polymer host and the structural properties of pure and complexed HPMC polymer electrolyte films were confirmed by X-ray diffraction (XRD) studies. XRD results revealed that the amorphous domains of HPMC polymer matrix were increased with increase in NaI salt concentration. The degree of crystallinity was found to be high in pure HPMC samples. The thermal properties were studied using differential scanning calorimetry (DSC). DSC results revealed that the presence of NaI in the polymer matrix increases the melting temperature; however, it is observed that fusion heat is high for pure HPMC films. The variation of film morphology was examined by scanning electron microscopy. Fourier transform infrared spectral studies revealed vibrational changes that occurred due to the effect of dopant salt in the polymer. Direct current conductivity was measured in the temperature range of 313–383 K. The magnitude of electrical conductivity was found to increase with the increase in salt and temperature concentration. The data on the activation energy regions (regions I and II) indicated the dominance of ion-type charge transport in these polymer electrolyte films. The composition HPMC:NaI (5:4) is found to exhibit the least crystallinity and the highest conductivity.