Disjoining pressure of discrete surface charges on thin aqueous films.

The disjoining pressure of charged parallel interfaces confining an electrolyte solution is to a large extent determined by the screening clouds of the surface charges. We evaluate the pressure in terms of the number density sigma of discrete charges and film thickness d and find, at sigmad(2) approximately 1, a crossover from the well-known law P approximately sigma(2) to a linear behavior P approximately sigma. For the latter case, each surface charge results in strongly inhomogeneous pressure profiles at both interfaces.