Ion-pairing effects on viscosity/conductance relations in Raman-characterized polymer electrolytes: LiClO₄ and NaCF₃SO₃ in PPG(4000)

Precise measurements of viscosity and conductivity have been made of the solutions of sodium triflate and lithium perchlorate in poly(propylene oxide) of MW 4000 (PPG(4000)) studied spectroscopically by Torell and co-workers for the extent of ion association. Viscosity, but not conductivity, data conform very well to the VTF equation and yield ideal glass transition temperatures that track the measured glass transition temperatures as closely as in the case of glass-forming aqueous solutions. The differences in temperature dependences of the two processes are demonstrated by using Walden rule plots. Using the data of Torell et al. at ambient temperature as a calibration point, we show that the deviations of conductivity from viscosity-dictated behavior predict almost quantitatively the strong temperature dependence of the free ion concentration found by Torell et al. up to the high temperature limit of their measurements.