Alkali Nafion, linewidths

The amount of broadening experienced by alkali metal ions upon binding to a polymer such as Nafion will depend on several factors including nuclear spin, electric quadrupole moment, stability of the hydrated ion, and electronic polarizability. This last factor relates to the ease with which electric field gradients can be produced by binding to an anionic site. Based on the relative change in linewidth upon going from saturation to low water contents, the ions studied so far are related... 

Alkali metal NMR spectra were observed at the appropriate resonance frequencies listed in Table I, using 12-mm tubes and a Varian XL-100 spectrometer with Gyrocode Observe capability. External 19F or internal H field-frequency lock was used. Depending on the linewidth of the resonance being observed, spectral widths of 256 Hz to 12 kHz in 8192 frequency domain points were used. For 23Na and 85Rb, 90° pulses of 50/isec and a 0.1-sec repetition rate were used. For 6Li and 133Cs, the approximately 55° pulses were 30 /xsec, and the pulse repetition rates for the Nafion samples were 60 sec and 1 sec, respectively. 

The larger linewidths observed for the alkali metal forms of Nafion relative to the corresponding model electrolytes indicate that ionic mobility is restricted because of ion binding to the polymer in the aqueous regions. Without additional studies it is not possible to obtain an estimate of relative binding strength from the data in Table VI. However, experiments identical to those for 23Na are possible in order to probe the hydration properties of these other ions in Nafion. 

---