A semiempirical quantum chemical study of some local aspects of ionic conduction in poly(ethylene oxide): Ion motion and rotational barriers

Several aspects of electronic potential energy curves for the ionic conduction process in poly(ethylene oxide) are modeled. A supermolecule is taken as a local model for a section of a polymer chain in the amorphous phase. Ion-polymer interaction, rotational barriers for the free and charged supermolecule, and the activation energy for intrachain ionic motion were calculated. For the latter, the oxygen-cation distance is considered as the reaction coordinate. The supermolecule assembly consists of five monomer units and a proton as probe ion. Strong coupling occurs between the motion of the ion and the flexional dynamics of the polymer that is manifest in the rearrangement that takes place in the nuclear framework of the chain as the position of the ion changes. The calculated activation energy was found in the range of the experimental values. All these results are consistent with the picture that ionic conduction in solid electrolytes such as poly(ethylene oxide) takes place mainly in the amorphous phase, because a considerable degree of flexibility on the polymer backbone is required to allow for the necessary bond rearrangements to promote cationic motion.