  We investigate ion and polymer dynamics in polymer electrolytes PPO-LiClO4
performing 2H and 7Li NMR line-shape analysis. Comparison of temperature
dependent 7Li and 2H NMR spectra gives evidence for a coupling of ion and
polymer dynamics. 2H NMR spectra for various salt concentrations reveal a
strong slow down of the polymer segmental motion when the salt content is
increased. The 2H NMR line shape further indicates that the segmental motion is
governed by dynamical heterogeneities. While the width of the distribution of
correlation times G(log tau) is moderate for low and high salt content, an
extremely broad distribution exists for an intermediate salt concentration 15:1
PPO-LiClO4. For the latter composition, a weighed superposition of two spectral
components, reflecting the fast and the slow polymer segments of the
distribution, describes the 2H NMR line shape over a broad temperature range.
Analysis of the temperature dependent relative intensity of both spectral
components indicates the existence of a continuous rather than a discontinuous
distribution G(log tau). Such continuous distribution is consistent with
gradual fluctuation of the local salt concentration and, hence, of the local
environments of the polymer segments, whereas it is at variance with the
existence of large salt-depleted and salt-rich domains featuring fast and slow
polymer dynamics, respectively. Finally, for all studied mixtures PPO-LiClO4,
the 2H NMR line shape strongly depends on the echo delay in the applied
echo-pulse sequence, indicating that the structural relaxation of the polymer
segments involves successive rotational jumps about small angles gamma<20
degree.

Materials Science