Dynamics of ion transfer potentials at liquid-liquid interfaces: the case of multiple species.

The dynamic evolution of a water-nitrobenzene system with both solvents containing an initially equimolar mixture of two monovalent binary electrolytes, sharing a common cation, is simulated using the Nernst-Planck-Poisson finite difference method. The effect of single ion partition coefficients and diffusion coefficients on the evolution of potential across the liquid-liquid interface is investigated. Two separable components of the potential difference are observed: a static component localized at the liquid-liquid interface and a diffuse component with dynamic spatial expansion. The former is shown through novel calculations to be dependent on an apparent partition coefficient of the system, defined to be dependent on the partition coefficients of the two constituent salts such that the static component also depends on the single ion partition coefficient of the shared cation. The dynamic component depends on the same apparent partition coefficient; further, its dependence on the diffusion coefficients of the constituent ions is investigated, and the time scales of the potential difference formation are revealed. The evolution of the system can be described in three stages with short time behavior dominated by partition of ions and long-time behavior dominated by recovery of electroneutrality. The dynamics were correlated to those recently discussed for a simpler system [Zhurov, K. et al. J. Phys. Chem. B, 2011, 115, 6909-6921].