Surface charge density on spherical silica particles in aqueous alkali chloride solutions

Abstract

Experimental data concerning the dependence of the surface charge density of AEROSIL 300 in aqueous alkali chloride solutions on pH are analyzed under application of two different models for a spherical electrical double layer. Data for the alkali ions Li+, Na+, K+, Rb+ and Cs+ are included at five electrolyte concentrations. In the first model a counterion binding in combination with a pure diffuse spherical double layer is considered; here, a good agreement between the recalculated plots and the experimental data is found for low electrolyte concentrations (c<0.05 mol/l) only. The second model with a charge free Stern layer and without counterion binding seems to be applicable for higher electrolyte concentrations also. Furthermore the surface charge density constants from the second model agree better with those published and determined with other models or experimental methods.