Electrical conductivity, viscosity, and density of a two-component ionic system at its critical point

Abstract

The density, viscosity, and electrical conductivity of a system composed of a fused salt in a low dielectric constant solvent were examined at a temperature just above the liquid-liquid critical point. The system examined was tetra-n-butylammonium picrate (TNBAP) in 1-chloroheptane. The conductivity decreased to a minimum near 0.001 mol/dm3 and then increased rapidly through the region of the critical concentration. The data in the region of the minimum were fit by using the method of Fuoss and Kraus to determine the ion-pair and ion-triplet dissociation constants. An extrapolation of these equilibria toward the critical region indicated a rapidly increasing importance of ion triplets at the expense of the neutral ion pairs. The conductivity results were also compared to a recent cluster-equilibrium treatment of the restrictive primitive model (RPM). This treatment of the RPM also shows an increasing importance of charged clusters, at the expense of neutral clusters, as the concentration approaches that of the critical point. The dielectric constant of 1-chloroheptane was also measured over a range of temperature.