Nuclear Magnetic Resonances Studies of Polymer Electrolytes.

^{23}Na NMR studies have been made on a variety of polymer electrolytes. Remarkably, the measurements reveal features that are common to nearly all types of material studied, including the presence of mobile and bound (aggregates) of sodium. T_1 's of the mobile and bound sodium are in the range of milliseconds and seconds respectively. The bound Na has a relatively temperature insensitive linewidth of about 5 kHz. The linewidth of mobile Na is typically 5 kHz below the glass transition temperature (T_{ rm g}), and undergoes motional narrowing above T_{rm g} (evidence of the importance of polymer segmental motion of the ion transport process) to a minimum of about 0.5 kHz at around 45-55 K above T_{rm g}, and then broadens somewhat. The broadening is due to the relatively fast spin-lattice relaxation time (T _1 ~ 300 mus), i.e. lifetime-broadening. The temperature dependence of the ratio of mobile to bound Na (M/B) indicates the process of ion dissociation and a minor role of thermal "carrier generation". A study of a series of poly(propylene-oxide)(PPO)NaI complexes of different salt concentration suggests that PPO _8NaI is the only stable amorphous phase in the complexes. Both T_1 and linewidth of the bound Na measurements show that bound Na is likely to be an ion-aggregate (~ 10 or more ions). The drop of M/B above 353 K indicates the occurrence of salt precipitation (SP). Ion-ion and ion-polymer interactions in polymer complexes are further investigated by measurement of a series of PPO complexes with different sodium salts. Satisfactory correlation between SP temperature and melting point of pure salt has been found. ^{23} Na chemical shifts due to mobile Na^+ ions exhibit a strong dependence on anion and temperature. Moreover, ^{13}C NMR data show differences in ion-polymer interaction for Li- and Na- PPO complexes. High pressure NMR of several PPO and siloxane complexes exhibit a systematic decrease in M/B with increasing pressure. In addition, the linewidth increases or decreases with the application of pressure, depending on the value of T -T_{rm g}. The results are consistent with collaborative high pressure conductivity measurements, which also indicate that T _{rm g} increases with increasing pressure. In multi-frequency ^{23 }Na NMR of PPO and siloxane-based complexes, the linewidth of the mobile Na^+ ion is inversely proportional to the resonance frequency, implying second order quadrupole broadening.