Conductivity and Viscosity of PC-DEC and PC-EC Solutions of LiBF[sub 4]

The conductivity κ of propylene carbonate-diethyl carbonate (PC-DEC) and PC-EC (ethylene carbonate) solutions of was experimentally determined at temperatures θ from 60 to −80°C and at salt molalities m from 0.2 to and solvent compositions w from 0 to 0.7 weight fraction of DEC for the former solution and from 0.3 to 2.7 of m and 0 to 0.6 of w of EC for the latter. Viscosity η of these solutions was also studied by measuring their glass transition temperatures in the same ranges of m and The was found to rise with and fall with w of DEC but rise with w of EC, indicating a concurrent change in the η of the solutions. The κ of the PC-DEC solution of peaked in both m and w thus forming a dome in its 3D presentation in the coordinates, while the κ of the PC-EC solution peaked only in resulting in an archshaped surface. As θ lowered, these κ surfaces fell in height and shifted in the direction of low η. These observations correlated well with the changes of dielectric constant ɛ and viscosity η of the solutions with the same set of variables. A more detailed study of the effects of DEC and EC on the κ of PC solution of demonstrated that ion association in these solutions was very weakly dependent on θ, in agreement with an earlier finding. The data of the PC-DEC solution was fitted with a Vogel-Fulcher-Tammann equation for an evaluation of its vanishing mobility temperature and apparent activation energy, both were shown to form simple surfaces in the coordinates slanting up in the direction of high η. Furthermore, when compared to the surface of the same solution, the surface was oriented similarly but lower in value by a few dozen degrees.