Equivalent circuit analysis of impedance spectra of semicrystalline polymer

Impedance measurements in the frequency range from 101 to 106 Hz are presented for poly(ethylene oxide) with molecular weight of 2000 g/mol during non-isothermal crystallisation and melting with different cooling/heating rates (5, 10 and 20 K/h). The impedance spectra are fitted using an equivalent circuit, which models high frequency capacitance, flat dielectric loss, ionic conductivity in multiphase structure, and electrode polarisation. The evolution of the spectra and the variation of the parameters of the circuit during crystallisation and melting processes are presented. For the semicrystalline polymer, conductivity dispersion is observed, and two apparent conductivity contributions can be separated. A model of semicrystalline polymer, comprising two phases, which exhibit high and low ionic conductivity, is discussed. A possible interpretation of the results in the frame of percolation network approach is indicated. Substantial differences between the mechanisms of melting and crystallisation are the main reason for occurrence of thermal hysteresis of conductivity.