Modelling of segmental dynamics in polymer electrolyte PPO-LiClO4, by surface fitting of quasi-elastic neutron scattering data

The structural dynamics of an amorphous model polymer electrolyte, poly(propylene oxide) (PPO) complexed with lithium perchlorate (LiClO4), has been investigated using quasi-elastic: neutron scattering (QENS). Pure PPO was investigated for reference. A combination of data from several analyser reflections, has enabled an investigation of a (Fourier) time range, wide enough to encompass parts of the segmental relaxation as well as the methyl group motion. The two processes have been identified and investigated by a simultaneous surface fit of the data from all the detectors and resolutions to a model where the segmental motion is represented by a stretched exponential relaxation function with relaxation times proportional to Q(-v), and the methyl group motion is represented by the three-fold jump rotation model. The dynamics of the pure polymer is well described by the model, using fitting parameters which are in good agreement with literature data, and we conclude that the surface fitting approach is a successful method for analysing the data. The results for the salt-containing polymer show that the segmental relaxation is strongly slowed down and more stretched, whereas no significant change was seen for the methyl group motion. The adequacy of the model in this case cannot be fully evaluated due to the still limited data on the segmental relaxation. (C) 1999 Elsevier Science B.V. All rights reserved.