NMR investigations of ionic host polymer systems.
NMR studies of the archetypal ionic host polymer system, in which
polyethylene oxide (PEO) forms the polymer host, and lithium
trifluoromethanesulphonate (LiCF3S03) is the guest ionic salt, are
reported. The work is primarily concerned with the ability of the polymer
host to incorporate the guest salt within its structure.
Studies of pure PE~, LiCF3S03 itself, and ionic host polymer systems of
O:Li ratios of 3.5: 1 and 9: 1 are reported in detail. A key experimental
approach is the use of spin-lattice relaxation time measurements (I H, 7Li
and 19F) to act as a probe of structure and dynamics.
19F spin-lattice relaxation time investigations in LiCF3S03 and
PEO/LiCF3S03 systems are interpreted in terms of a mechanism in which
the hindered reorientation of CF3 groups plays a key role. Crosscorrelations
are shown to be responsible for non-exponentiality in nuclear
magnetization recoveries. The problem of defining and measuring spinlattice
relaxation times in these circumstances is considered in some detail.
In the ionic host polymer systems an additional spin-lattice relaxation
mechanism is that due to 19F_I H cross-relaxation. A model is developed
to simulate the key features that can be observed experimentally for this
type of mechanism. 7Li spin-lattice relaxation time studies in LiCF3S03
and PEOILiCF3S03 systems are also reported. In the salt a heteronuclear
dipolar coupled 7Li_19F spin-lattice relaxation mechanism is shown to be
dominant. T,he predicted relaxation behaviour is calculated in detail from a
proposed crystal structure. I H lineshape and spin-lattice relaxation time
measurements are reported in PEO and PEOILiCF3S03 systems.
Overall, no evidence is found for the existence of the CF3S03- anion in the
amorphous phase of the PEO/LiCF3 SO 3 systems studied. Hindered
reorientation of the CF3 group also occurs in these systems, with a similar
activation energy to that found in the salt itself. However, there is
evidence that the 7Li+ cation can move between crystalline and amorphous