Quasi-Elastic Neutron Scattering Investigation of Dynamics in Polymer Electrolytes

Abstract

Polymer dynamics in a cross-linked poly(ethylene oxide-propylene oxide) random copolymer, both neat and doped with an inorganic salt, is investigated by means of quasi-elastic neutron scattering (QENS) as a function of temperature and momentum transfer. Data from a high-resolution backscattering instrument are reported. We present an original approach to the analysis of inelastic fixed energy scans. The findings from this approach lead to a detailed description of the polymer dynamics across the glass transition. The neat polymer dynamics is modeled in terms of two relaxation processes: Below the glass transition, the methyl side group hopping relaxation has been characterized and compared with the similar process occurring in pure poly(propylene oxide). Above the glass transition, a non-Debye, non-Arrhenius relaxation occurs, corresponding to the polymer segmental dynamics. In the case of the salt-doped rubber, the segmental dynamics is found to be more complex: while the methyl group dynamics is not affected by the salt addition, the present data set supports the view of a bimodal segmental dynamics as a consequence of salt addition.