Dynamic theory of type 3 liquid junction potentials: formation of multilayer liquid junctions.

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.