Structural and electrical properties of poly(ethylene oxide)-cadmium sulphate complexes

Solid complexes of poly(ethylene oxide), PEO and 3CdSO4.8H2O varying from 0 to 25 wt% corresponding to solubility limit Cd2+/EO=0 to 0.019 were prepared by the solution cast technique. X-ray diffraction (XRD) technique shows the presence of a new crystalline phase at Cd2+/EO>0.009. Two new peaks are observed at 2θ≈16° and 27° which is not attributable to PEO or 3CdSO4.8H2O. These peaks increase in intensity and are accompanied by other peaks as indicated in the diffractograms for samples with higher doping concentration. At low salt concentrations Cd2+/EO<0.009, X-ray diffraction infers the disruption of the crystalline order of the PEO and their conversion to the amorphous state. The cations Cd2+ and anions [SO4]2− are therefore dispersed in the amorphous phase of the PEO. The increase in salt concentration in the low salt regime (Cd2+/EO<0.009) increases the amorphous nature of the PEO. This is verified by the variation of the coherent or Scherrer length with Cd2+/EO ratio and implies that the highest conducting film is the least crystalline in nature. Absorption spectroscopy shows the occurrence of polymer–salt complexation which involves an interaction between the cation of the salt and the lone pair electrons of the ether oxygen atom. This can be inferred from the peaks present at 1395 and 1912 nm, respectively. Infrared spectra show some shifts in the spectral bands which could be attributed to complexation. Overlapping of some PEO and 3CdSO4.8H2O bands in the region 1000–1500 cm−1 makes such analysis difficult. Ionic conductivity in these electrolytes was studied by impedance measurement in the frequency range between 40 Hz and 100 kHz. The highest conductivity at room temperature was 5.5×10−7 Scm−1 for the polymer film with solubility limit of Cd2+/EO=0.009 at 5 MPa pressure. The transference number is ∼0.7. Some electrochemical cells were fabricated.