Ionic conduction in LiScn/Dimethylformamide/Poly(propylene oxide) system II. Mobility of lithium and thiocyanate ions

Ionic conductivity σ, shear viscosity η, and glass transition temperature T_g were measured on systems composed of lithiumthiocyanate LiSCN, N,N-dimethylformamide (DMF), and poly (propylene oxide) (PPO) over wide ranges of LiSCN concentration C and DMF content Φ. Using the dissociation constant of LiSCN reported in Part I, we have determined the concentration n of Li⁺ and SCN^? ions and then the mobility μ from σ. Data indicate that in the binary system of LiSCN/PPO, the σ versus C curve exhibits a maximum ca. C = 0.3 mol/L. In low C range, μ is independent of C but decreases with C in the range of C > 0.3 mol/L. Similar n dependence of μ is seen in the ternary systems containing DMF. The ratio of μ₀/μ (C) is lower than the ratio of viscosity η(C)/η₀ where μ₀ and η₀ indicate the values at infinite dilution of LiSCN. Thus the friction coefficient ?_ion for the translational diffusion of the ions is not proportional to the macroscopic viscosity. Relationship between μ and the monomeric friction ?_p for the segmental motion of the PPO chains is also discussed based on the data of T_g and the Williams-Landel-Ferry equation. ©1995 John Wiley & Sons, Inc.