ELECTROSTATIC REPULSIONS BETWEEN HIGHLY CHARGED PLATES IN ELECTROLYTE-SOLUTIONS - LIMITING LAWS FOR LARGE AND SMALL SEPARATIONS

Two limiting laws for electrostatic repulsions between highly charged surfaces in solutions of strong electrolytes are derived from the linear double layer theory (J.J. Spitzer, Nature, 310 (1984) 396; Langmuir, 5 (1989) 199) for the limits of infinitely large and infinitely small separations. The limiting law for the very large separations gives a new explicit dependence of the repulsive pressures on the charge type of electrolyte, both symmetrical and unsymmetrical, while maintaining the exponential decay of the repulsive forces. In the limit of very close separations the repulsive pressures are inversely proportional to the square of separation. Their very weak dependence on ionic strength disappears altogether in the limit of zero ionic strength. These repulsive forces have the characteristics of "hydration" forces, i.e. they are very large and nearly independent of ionic strength.