The Application of the Gouy Theory to Soil‐Water Systems

Abstract This paper shows how the Gouy theory may be used to describe the properties of soil and clay suspensions. The volume charge density and the potential distribution in a single layer may be calculated for widely different clay suspensions if the surface density of charge and the concentration of free electrolyte are known. The interaction between two diffuse double layers of adjacent particles leads to a differential equation describing the volume charge and potential distribution that can be solved only for suspensions containing symmetric electrolytes. Sufficiently accurate approximations of the charge and potential distribution may be made, however, for suspensions containing asymmetric electrolytes. Due consideration must be given to the specific adsorption potential of ions in the Stern layer. By means of the Gouy theory it is possible to calculate such measurable quantities as negative adsorption, osmotic pressure, and membrane potential. A comparison of the applicability of the Donnan and the Gouy theories shows that the Gouy theory is superior in describing and predicting the properties of deflocculated clay suspensions. Indeed, the application of the Donnan theory to such systems leads to serious errors.