Electroconvection at an electrically inhomogeneous permselective membrane surface

Abstract

This paper describes electroconvection, a non-gravitational free convection which may arise in macroscopic domains of electrolyte solution. Electroconvection originates from the interaction of a self-consistent electric field with the corresponding space charge within the limits of validity of local electroneutrality approximation. The electrodiffusional Peclet number is defined and is shown by dimensional analysis to be universally of the order of unity, independent of the system's size and typical electrolyte concentration. Electrodiffusional ionic concentration and electric potential fields, which form in the course of concentration polarization at an electrically inhomogeneous cation permselective periodic membrane, are calculated. It is shown that these fields are incompatible with mechanical equilibrium of the ionic fluid, that is electroconvection is bound to arise in this constellation. Results of numerical computations in a two-dimensional model of electroconvection flow at a conductively inhomogeneous periodic membrane are presented along with some explicit expressions for the electroconvectional flow rate, obtained through an asymptotic analysis, valid in the vicinity of electrodiffusional limiting current.