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(pro pylene oxide) (PPO) complexed with lithium perchlorate (LiClO4), has been i nvestigated using quasi-elastic: neutron scattering (QENS). Pure PPO was in vestigated for reference. A combination of data from several analyser refle ctions, 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 simul taneous 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 m ethyl group motion is represented by the three-fold jump rotation model. Th e dynamics of the pure polymer is well described by the model, using fittin g parameters which are in good agreement with literature data, and we concl ude that the surface fitting approach is a successful method for analysing the data. The results for the salt-containing polymer show that the segment al relaxation is strongly slowed down and more stretched, whereas no signif icant change was seen for the methyl group motion. The adequacy of the mode l in this case cannot be fully evaluated due to the still limited data on t he segmental relaxation. (C) 1999 Elsevier Science B.V. All rights reserved .