A model equation for the gravielectric effect in electrochemical cells.

The gravielectric effect model equation for a single-membrane system was elaborated. This model for binary and ternary ionic solutions was verified using a cell with a horizontally mounted membrane. In this cell, the membrane and transition potentials were measured as a function of gravitational configuration. In these experiments, a 0.001 M aqueous solution of sodium chloride was placed on one side of the membrane. The opposite side of the membrane was exposed to either aqueous sodium chloride solutions, with densities greater than that of 0.001 M aqueous NaCl, or ethanol/NaCl/water solutions. On the basis of the experimental results, the influence of constrained release and the gravielectric effect were established. These experimental findings are interpreted in terms of a convective gravitational instability that reduces boundary layer dimensions and increases the permeability coefficient of the complex system: boundary layer/membrane/boundary layer. A concentration-gradient Rayleigh number is used in a mathematical model for gravitationally sensitive membrane potential.