Electrophoretic mobility of latex spheres in mixture solutions containing mono and divalent counter ions

The electrophoretic mobilities of polystyrene sulfate latex spheres carrying constant surface charge densities in aqueous solutions were measured in the presence of monovalent K+ and divalent Mg2+ counter ions. The measurements were carried out as functions of the concentrations of Mg2+ and K+ ions (CMg and CK) and the ratio of the concentration of divalent counter ions to that of monovalent ions, X = CMg/CK. The data were analyzed on the basis of standard electrokinetic and electric double layer models. The calculated values of the mobility are in reasonably good agreement with the experimental data assuming that the distance of the slipping plane from the surface, xs ranges from 0 to 0.25 nm and the values of xs increase with increasing X.

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► We measured electrophoretic mobility of sulfate latex particles in mixed solutions of KCl and MgCl2.
► Increase of divalent counter ions effectively reduces the absolute value of the mobility.
► Standard electrokinetic theories with constant surface charge density describe the experimental data.
► The distance to slipping plane is located at 0–0.25 nm from particle's surface.
► The distance to the slipping plane increases with increasing the ratio of Mg2+ concentration to K+ concentration.