Thermal-dependent morphological evolution effect on ion transportation in polyethylene oxide films

Abstract

PEO films were prepared on glass substrates from dissolved PEO powder in methanol using the solution casting technique. The investigation of these PEO films involved the utilization of Atomic Force Microscopy, Dielectric Relaxation, and Nuclear Magnetic Resonance techniques to explore alterations in the morphology of the polyethylene oxide polymer films as a response to consecutive thermal cycling at various heating and cooling rates. The dielectric loss curve dependency on frequency for each temperature point within the thermal cycles was fitted with a Havriliak–Negami function with an electrical conductivity contribution. The relaxation times associated with the α- and β-relaxation processes were determined by applying the Arrhenius temperature law, enabling the calculation of the respective activation energies. The study reveals the influence of heating rates on the reversibility of dielectric permittivity, dielectric loss, and dielectric strength, which remains consistent at 2 K/min but not at 0.35 K/min. It also emphasizes the impact of crystallinity on the electrical conductivity of PEO films, highlighting the significance of the amorphous state. The investigation of activation energies for β-relaxation and α-relaxation reveals values of 0.40 eV and 0.74 eV, respectively, in line with similar materials. 1H NMR spectra were studied to differentiate between the crystalline and amorphous phases. The peaks corresponding to the crystalline phase exhibit broad NMR signals with overlapping characteristics attributed to the diverse crystalline structural environments that are present.