An Analytic Expression for the Particle Size Dependence of the Surface Acidity of Colloidal Silica

Abstract

The charge formation on colloidal silica particles in aqueous solutions is described as a dissociation of acid silanol groups. For the relationship between surface charge density and surface potential on spherical particles an approximate solution of the spherical Poisson-Boltzmann equation, given by Ohshima et al., is used. An analytic equation describing the dependence of the apparent acid constant, K app S, on the degree of dissociation of surface silanol groups is derived, as is an analytic expression for calculating surface charge density-pH presentation. Surface charge density measurements on spherical silica particles of different sizes in aqueous 1-1 electrolyte solutions of different ionic strength are carried out using potentiometric titration.