The objective of this presentation is to elucidate the structure-dynamics-property relationships that underpin the performance of ion containing polymers as membranes in electrochemical energy storage and delivery technologies. We leverage quasielastic neutron scattering to quantify the dynamics within the polymeric membrane on the nano- to picosecond time scales over length scales of few angstroms to several nanometers in a series of model single ion conducting polymers, where only the cation is mobile, with systematic variations in the spacing between the ions, degree of ionization, and the type of ion. Variations in the nature of the polymer dynamics on these times and lengths scales are compared with changes in the mobility of the free ions as quantified by impedance spectroscopy. Preliminary measurements show that on the nano- to picosecond time scale the polymer relaxations can often be described by a summation of 3 different relaxation processes. The slowest, least mobile of the 3 processes generally looks purely diffusive and shows a normal thermal activation. An intermediate and more mobile process often shows strong signs of confinement; the relaxation is almost independent of Q, indicated a strongly caged type motion. However, the fastest process usually falls between the extremes of confinement and free diffusion. The motion is characteristic of jump diffusion with a characteristic residence time and jump length. Furthermore, in some cases there is clear evidence of this motion slowing down upon heating, the opposite of normal thermal excitation. In these cases the slowing down with upon heating is correlated with the appearance of ionic aggregates in the temperature dependent X-ray scattering. In this presence the relationship between the nature of these ionic aggregates, the intrinsic mobility of the polymer membrane, and the transport properties will be examined in detail.

Fast dynamics, structure, and transport in ion containing polymers

248th National Meeting (2014)

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