Conductivity enhancement due to ion dissociation in plasticized chitosan based polymer electrolytes

Cast films of chitosan acetate, plasticized chitosan acetate, chitosan acetate containing salt and plasticized chitosan acetate-salt complexes were used to obtain some insight on the mechanism of ionic conductivity in chitosan-based polymer electrolytes. The films are largely amorphous. The conductivity is due to the mobile ions from the salt. The role of the plasticizer is to dissociate the salt thereby increasing the number of mobile ions, which lead to conductivity enhancement. The conductivity was calculated using the bulk impedance obtained through impedance spectroscopy. The Cole-Cole plots illustrating the variation of the negative imaginary impedance with the real impedance do not always shaw the double layer reactance but the plot of dielectric constant epsilon (r) versus frequency tends to a maximum at low frequencies. The real and imaginary parts of the electrical modulus of samples containing salt show a "long tail" feature, which is not found in the electrical modulus spectra of the unsalted samples. This long tail feature can be attributed to high capacitance, which further supports the plasticizer's role as an agent to dissociate the salt into ions. (C) 2001 Elsevier Science Ltd. All rights reserved