Effect of electrolyte type on the electrophoretic mobility of polystyrene latex colloids

Abstract

Electrophoretic mobility studies of surfactant-free polystyrene latex particles in various types of inorganic electrolytes are reported. The particles carry sulfate functional groups and cover a wide range of surface charge. The electrophoretic mobility curves of all latices exhibit a pronounced maximum as a function of 1:1 electrolyte (KCl) concentrations. With 2:1 and 3:1 electrolytes (CaCl2 and LaCl3 respectively), the electrophoretic mobility curves pass through a minimum followed by a maximum. The results are discussed in terms of models that have been previously proposed to explain these maxima in the mobility curves. Our results suggest that the increase of mobility with salt concentration may be attributed to the approach of co-ions close to the hydrophobic surface of the particles. It is also suggested that three competing processes at the interface determine the shape of the mobility curves.