Characterization of the electrical double layer of montmorillonite

The primary objective of this paper was to determine the relative magnitudes of ψo, ψδ, and ζ, the electrostatic potentials in the plane of the clay-water interface, the outer Helmholtz plane, and the plane of shear, respectively. Another objective was to determine the relative magnitudes of σo and σδ, the charge densities in the first two planes, respectively. Four different methods were used to achieve these objectives. All of them gave the same results. The results were interpreted to mean that most of the exchangeable cations are condensed on the montmorillonite surface in a Stern layer and that adjustments in the ionic occupancy and/or thickness of this layer maintain ψdelta at a constant, critical value that cannot be exceeded.