The segmental dynamics of a polymer electrolyte investigated by neutron spin echo technique

Abstract

The structural dynamics of a polymer electrolyte model material, PPO-LiClO4, has for the first time been studied using the Neutron Spin Echo technique. The dynamics was studied at a Q-value close to the first sharp diffraction peak, which has been shown originate from inter-chain correlations. Pure PPO was investigated for reference and we find for both materials, that a stretched exponential function can describe the relaxation observed, and that the relaxation times are, within the compared temperature range, proportional to reported relaxation times from viscosity measurements. We therefore attribute the observed dynamics to α-relaxation and ascribe an inter-chain character to it. The relaxation of PPO-LiClO4 is found to be slower and more stretched compared to that of pure PPO, which, with the inter-chain character of the relaxation in mind, may be attributed to that the salt induced transient cationic cross links between chains. We furthermore find that the shape of the α-relaxation in PPO (stretching parameter β), as obtained in the present NSE experiment, is not compatible with results from dielectric spectroscopy or photon correlation spectroscopy.