Precipitation membranes: III. Reversible changes of membrane properties induced by alterations in ionic concentrations.

The conditioned state of a precipitation membrane with its particular properties exists within a limited range of membrane potentials and requires certain minimum concentrations, Clim, of the generating ions in the adjoining solutions. We investigated these quantities for the BaSO4 cellophane membrane and found Clim to be 10 X 10(-5) N (0.5 X 10(-4) M), equally for Ba++ and SO4--. Beyond these limits, the membrane becomes deconditioned. This transformation is a reversible process provided the limits have not been surpassed too far. The capability for de- and reconditioning is a characteristic and unique property of precipitation membranes, not found in other membrane systems. The phenomenon is explained by the adsorption theory for precipitation membranes. It allows wide modifications and quick variations of the electrical properties and permeability of the membrane in an easy and reversible manner.