Thermodynamic approach to the interpretation of electrokinetic data near the isoelectric point

Abstract

A theorem derived previously is used to provide a thermodynamic approach to the interpretation of electrokinetic data which is more general and more soundly based than previous treatments and which requires fewer assumptions. Concepts such as wall potential, adsorption plane and inner region capacitance are not required. An expression for the dependence of zeta potential on concentration of potential determining ion at the isoelectric point (i.e.p.) is shown to be independent of any detailed model for the inner regions of the double layer. For some systems relationships between amounts specifically adsorbed, Γ_i, and bulk concentrations, n_i, are obtained from a virial expansion of the surface pressure, Π, in terms of the Γ_i when the Γ_i are small. This procedure avoids the ad hoc assumptions made previously to obtain similar results. The treatment of systems containing ionic surfactants is made more general and placed on a firmer basis.