The limiting concentration dependence of the heat of transport in electrolyte solutions

The limiting concentration dependence of the heat of transport of electrolyte solutions has been investigated. The ionic contribution to the Onsager phenomenological coefficients for heat-matter coupling L_qi have been calculated by the time-correlation function method using the Fokker-Planck operator as the time-evolution operator. It is shown that the limiting slope due to the direct ion-ion electrostatic effect obtained in the present work agrees with the result in the literature. It is also shown that the contribution to the limiting slope due to ion-solvent interaction may be written in terms of the differences in the Stokes law radii of the ions as well as the reduced ionic heats of transport at infinite dilution. Although our result resembles Agar's result based on a hydrodynamic theory, we point out that there exist substantial differences in the implications of the two results. Finally, an error in the theory of Kahana and Lin [J. Chem. Phys. 75, 5043 (1981)] has been uncovered and corrected.