The segmental dynamics of a polymer electrolyte investigated by coherent quasielastic neutron scattering

Abstract

The structural dynamics of a polymer electrolyte model material, poly͑prolyene oxide͒ (PPO)-LiClO 4 ͑and PPO for reference͒, has for the first time been studied using coherent quasielastic neutron scattering. By a combination of neutron spin echo and inverse time-of-flight techniques we investigate the relaxation function in an experimental time window 10 Ϫ12 Շt Շ10 Ϫ8 s at a momentum transfer corresponding to the distance between neighboring interchain segments. We find that the relaxation of the correlation between neighboring chains is slower and more stretched in the polymer salt complex compared to the pure polymer. The data can, for both PPO and PPO-LiClO 4 , be described by a stretched exponential function with temperature independent stretching parameters. While the relaxation times follow the macroscopic viscosity for the former, they do not for the latter. The slower relaxation in PPO-LiClO 4 compared to PPO and the failure of the viscosity scaling in PPO-LiClO 4 may be explained in terms of a temperature dependent effective molecular weight induced by cations acting as cross links between chains. We discuss the origin of the extra stretching of the relaxation in the polymer salt complex under the aspect of heterogeneity, comparing it with data in the literature. We find that the stretching to the major part is intrinsic or at most due to heterogeneities on an atomic length scale. The molecular length scale of the experiment allows for the first time a direct connection to the renewal time in the dynamic disordered hopping model for ion transport in polymer electrolytes.

Ion and polymer dynamics in polymer electrolytes PPO-LiClO4. I. Insights from NMR line-shape analysis

“…8,14 Two limiting scenarios can explain such nonexponential relaxation. 8,14 Two limiting scenarios can explain such nonexponential relaxation.…”

“…Following the common nomenclature in the literature, 8,[13][14][15]21 we disregard the difference between PPO and PPG and refer to the studied polymer as PPO. PPO ͑M w = 6510 g / mol͒ and LiClO 4 were purchased from Polymer Source Inc. and Aldrich, respectively.…”

“…8,12,14,16,17 This effect was regarded as a consequence of cations acting as transient intra-or intermolecular cross-links between different monomers, leading to a reduction of chain flexibility. For PPO as host polymer, it was established that addition of salt slows down the polymer dynamics.…”

Molecular-dynamics simulation of structural and conformational properties of poly(propylene oxide)

“…This opens the possibility to investigate and scrutinize in detail the relaxation dynamics of PPO, measured in recent inelastic neutron scattering studies. 35 These results will be presented separately. The accuracy of the model makes an extension to polymer electrolytes very tempting.…”

Macromolecular structural dynamics visualized by pulsed dose control in 4D electron microscopy

“…Because of its fundamental properties and a whole range of applications (14)(15)(16), thermodynamic and static-structure studies of PEO have been made using a plethora of experimental techniques (e.g., [17][18][19][20][21]. However, investigations of structural dynamics have been mainly focused on local segmental motions in the chains using molecular dynamics simulations and frequencydomain dielectric spectroscopy and neutron scattering (22)(23)(24)(25).…”