Streaming potentials and conductivities of latex plugs. Influence of the valency of the counterion

Plugs consisting of polystyrene particles with sulphonate surface groups have been investigated in the presence of mono-, di- and trivalent counterions. The streaming potentials and conductivities of the plug and bulk solution have been measured. From the latter, the overall surface conductivity has been estimated. It is shown that for this system, accounting for the surface conductivity in the hydrodynamically stagnant layer is crucial to convert the streaming potentials into zeta potentials. The overall surface conductivity clearly depends on the charge of the counterion, and so do the ionic mobilities in the stagnant layer. The higher the valency of the counterion, the lower is the ionic mobility in the stagnant layer, but for all counterions, the ionic mobility in the stagnant layer is of the same order of magnitude as in the bulk. For the divalent counterions, no indications of specific interactions with the surface groups have been found.