Study of tetraalkylammonium salts in acetonitrile solutions: Transport properties, density, thermal expansion and phase transitions

Abstract

The electrical conductivity of binary solutions of tetraethylammonium trifluoromethanesulfonate ([TEA][OTf]), tetraethylammonium tetrafluoroborate ([TEA][BF4]) and spiro-(1,1′)-bipyrrolidinium tetrafluoroborate ([SBP][BF4]) in acetonitrile was measured at atmospheric pressure in the temperature range of 293.15–348.15 K for different salt mole fractions. The highest electrical conductivities of the acetonitrile solutions of [TEA][BF4], [SBP][BF4] and [TEA][OTf] were 96 ± 7, 94.5 ± 0.5 and 71.6 ± 0.5 mS·cm−1, respectively, at 348.15 K. The activation energy of the conductivity for nonassociating electrolytes was calculated using the Arrhenius equation, and the activation energy of the ionic conductivity of glass-forming liquids was calculated using the Vogel-Fulcher-Tamman equation. The cation and anion diffusion coefficients in the [TEA][OTf], [TEA][BF4] and [SBP][BF4] solutions in acetonitrile were determined by the robust pulsed-gradient stimulated echo sequence technique. Experimental density data were used to calculate the isobaric thermal expansion coefficients in the temperature range of 293.15–348.15 K. The thermophysical properties (the temperatures and heats of the phase transitions and the melting temperatures) of the pure salts and their binary solutions in acetonitrile were determined by differential scanning calorimetry.