Frequency-Domain Investigation of the Ionic Mobility of Triflate Salts in Tetrahydrofuran

Abstract

The frequency-dependent molar conductivities of two triflate salts, tetrabutylammonium triflate (TBATf) and lithium triflate (LiTf), in tetrahydrofuran are measured in the microwave frequency domain at the concentrations where the direct-current molar conductivity increases with concentration. The relaxation frequency of the conductivity of TBATf increases with concentration as was demonstrated by a simulation and theoretical calculation on a simple model system. However, the low-frequency side of the relaxation of the conductivity of LiTf grows with increasing concentration, suggesting the presence of large aggregates such as triple ions. The molar conductivities of both salts at 20 GHz are about an order of magnitude smaller than those predicted by the Nernst-Einstein relationship, indicating the importance of the picosecond or faster dynamics in the determination of the absolute value of the conductivity.