Relationship between diffusivity and viscosity for supersaturated electrolyte solutions

Abstract

Highly supersaturated electrolyte solutions are prepared and studied employing an electrodynamic levitator trap (ELT) technique. Very high supersaturations were achieved and studied. The theoretical study is based on the development of the Cahn-Hilliard formalism for electrolyte solutions. A correspondence of 96–99% between theory and experiment for all the solutions studied was achieved and reported earlier [Izmailov, Myerson and Na, Phys. Rev. E 52 (1995) 3923]. The theoretical approach suggested in this study for thermodynamics of supersaturated electrolyte solutions is further developed in order to describe the transient and stationary limits of the metastable state relaxation. Knowledge of these limits has allowed derivation of the fluctuation-dissipation theorem (FDT) for supersaturated electrolyte solutions by specifying a time-dependent product of macroscopic mobility (inverse viscosity), describing momentum dissipation, and microscopic diffusivity, describing local fluctuations of solute concentration. It is understood from general relationships of non-equilibrium thermodynamics that this product has a maximum at saturation point and is equal to zero at spinodal point. Further analysis of the FDT has revealed that the product has another particularity: a local minimum in the deeply undersaturated region of solute concentrations. Numerical analysis of the FDT has been carried out for the supersaturated, binary, electrolyte symmetric solutions such as NaCl, NaBr, KCl, KRr and NH 4Cl.