On the invariance of the charge of electrical double layers under dilution of the equilibrium electrolyte solution

Abstract

Electrical double layers are discussed in which the interfacial charge arises from the adsorption equilibrium between the interface and an electrolyte solution. A Gouy ionic atmosphere extends from the interfacial region into the solution. It is shown that for high potentials the interfacial charge is invariant under dilution of the electrolyte solution, provided that all counter ions have the same valency. This invariance rule applies to site binding of counter ions, and is demonstrated for a partially ionized fatty acid monolayer on the basis of a Gouy-Langmuir model. Similarly, for high potentials the adsorption of counter ions in an interfacial solution region (Stern layer) is invariant under dilution. The effects of geometry (plane, cylinder, sphere) are investigated, and applications to detergent micelles and to DNA are briefly discussed.