The effects of the overlap of double layers on electrophoretic mobilities of polydisperse suspensions

Abstract

The mutual interpenetration of the electric double layers of particles in aqueous suspension reduces the electrokinetic potential to a value below that of an isolated particle of the same surface charge and potential distribution. A theoretical treatment of this effect was developed by Möller, van Os, and Overbeek and shown by them to apply to solutions of bovine serum albumin. We have found that the same effect occurs with a polydisperse lyophobic suspension of colloidal silica under conditions of complete deflocculation. The behavior of the deflocculated polydisperse suspension can be matched with that of either of two theoretical monodisperse models, the particle sizes of which correspond to the weight average and number average, respectively, of the heterogeneous dispersion. In the presence of flocculating concentrations of electrolyte another effect is simultaneously apparent, namely, a tendency to increase the electrophoretic mobility, presumed to be caused by the presence of aggregates (doublets and triplets).