Electrokinetic measurements on concentrated polystyrene dispersions and their theoretical interpretation

Data on electrical resistances, streaming currents, and streaming potentials are reported for plugs of monodisperse spherical polystyrene particles in aqueous solutions. Three different surface charge densities were used and a wide range of KCl concentrations is covered. In the interpretation capillary models, accounting for double-layer overlap, and cell models, comprising polarization effects, are considered. Due to short-circuiting of the double layers the plugs must be considered as anisotropic, despite the sphericity of the constituting particles. Although the capillary approach thus seems to be favored, polarization phenomena dominate the effect of double-layer overlap. The two effects together are insufficient to explain the concentration dependency of the various experimental parameters. The surface of the polystyrene particles is presumably covered with a flexible layer (“hairy” layer), the thickness of which increases with decreasing ionic strength. Consequently, a substantial part of the conductance takes place through this hairy layer behind the slipping plane, a phenomenon known as anomalous conductance.