Insights into ion transport in biodegradable solid polymer blend electrolyte based on FTIR analysis and circuit design

This study reports the use of the solution casting method to prepare a biodegradable polymer blend electrolyte composed of chitosan (CS) and potato starch (PS). Different concentrations of potassium thiocyanate (KSCN) salt as an ionic provider were added to the CS:PS host. The results of X-ray diffraction (XRD) revealed a substantial reduction in the crystalline phase of the host polymers of up to 40 wt% of the added KSCN salt. Fourier transform infrared (FTIR) spectroscopy was used to detect microstructural modifications to the films to explore the complexation between the blended polymer chains and ions of the salt. Deconvoluted FTIR spectra were used to compute the free ions, contact ion pairs, and ion aggregates, which were then used as a sensitive method to determine the parameters of ion transport, including mobility (mu), carrier density (n), and the diffusion coefficient (D). Electrochemical impedance spectroscopy (EIS) was used based on electrical equivalent circuit modeling to study the electrical properties of the electrolyte films. A circuit design for each electrolyte was presented based on the curves of fitting of the EIS data. The parameters associated with elements of the circuit were of significant interest, especially for determining the conductivity of the films. The sample with the highest KSCN concentration of 50 wt% exhibited a reduction in conductivity due to the formation of ion pairs, the recrystallization of salt, and a decline in the amorphous fraction of the system, which was also visualized from its surface morphology by using an optical microscope. An analysis of properties of the dielectric manifested an enhancement upon the addition of salt, with characteristics of dispersive relaxation that verified the non-Debye behavior of the solid polymer electrolyte films. This behavior was further confirmed through the appearance of a distorted arc in the Argand plot. A decrease in the relaxation time was noted with the addition of salt, where this was in agreement with the results of EIS and AC conductivity measurements. An examination of the electric modulus revealed the process of viscoelastic relaxation whereby ion hopping was supported by coupling with segmental chain dynamics.