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Dynamic Theory of Type 3 Liquid Junction Potentials: Formation of Multilayer Liquid Junctions

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journal contribution
posted on 08.04.2010, 00:00 by Kristopher R. Ward, Edmund J. F. Dickinson, Richard G. Compton
A Nernst−Planck−Poisson finite difference simulation is used to model the dynamic evolution of a series of liquid junctions of the type A+X|B+Y, in which all ionic species are monovalent and present in equal concentration (a subset of Lingane’s type 3), from a nonequilibrium initial condition to a condition of steady-state potential difference. Simulations are performed in a linear space without constrained diffusion. Analysis of the dynamics shows very good agreement with recently presented revisions for the type 1 and 2 cases [J. Phys. Chem. B 2010, 114, 187−197] Considerable deviation of the value of the limiting liquid junction potential from that predicted by the classical Henderson equation [Z. Phys. Chem. 1907, 59, 118−127] is shown in many cases and investigated as a function of the size of the various diffusion coefficients. Significantly, the formation of a “multilayer liquid junction”, characterized by the existence of more than one instantaneous point of electroneutrality and thus more than one stationary point in the electric field (in a finite range of space), is inferred for the first time in a number of cases. The conditions for such a multilayer liquid junction are determined.