(401c) Effect of Complex Surface Chemistry on the Electrophoretic Mobility of Colloidal Particles
Colloidal stability of charged nanoparticles dispersions is a crucial property for almost all their applications, both when long shelf life is sought, and when coagulation has to be indiced before further processing. DLVO theory has been widely used to quantitatively determine colloidal stability of nanoparticles, and good results have been obtained provided that the surface properties of the nanoparticles are sufficiently well characterized. Recently, a generalized model for the colloidal stability of the nanoparticles has been proposed in the literature, which accounts for a variety of complex phenomena that occur at the surface of a charged nanoparticle, such as counterion binding, complex charge regulation models and surfactant adsorption equilibrium. One its major drawbacks is the large number of parameters required to describe all the equilibria at the particle surfaces. In this work, we present a new method to determine many of these parameters. First, a mathematical model for electrophoretic mobility of a nanoparticles has been developed by extending O'Brien and White approach to accommodate the complex surface chemistry, such as the charge regulation, the counterion binding, the surfactant adsorption etc.. The predictions of this model are compared to those of the more traditional approach assuming constant surface potential. Subsequently, electrophoretic mobility of colloidal nanoparticles have been measured through phase analysis light scattering as a function of pH and of electrolytes concentration, for different electrolytes containing the ions involved in the surface equilibria. By fitting all of the titration curves with the model, the different parameters of the model can be accurately estimated.