On the zeta-potential of sulfonated polystyrene model colloids

Abstract

Highly sulfonated polystyrene latex particles were prepared by a two-stage "shot-growth" emulsion polymerization process in the absence of emulsifier. Sodium styrene sulfonate was used as an ionic comonomer to produce latex particles with the same particle size and different surface charge densities. The conversion of electrophoretic mobility measurements into zeta-potential (ξ) data was carried out according to several theoretical approaches: Smoluchowski, O’Brien and White, and Dukhin and Semenikhin. The current electrophoretic theories give rise to a maximum in ξ-potential. Thisd behavior contradicts the classical electric double layer (e.d.l.) models which predict a continuous decrease in the electrokinetic potential. These theoretical approaches assume the absence of ionic conduction inside the shear plane. Dukhin and Semenikhin have developed an attempt to account for this phenomenon theoretically. In this work, we have calculated the ξ-potential of sulfonated polystyrene latex particles in the presence of symmetrical 1:1 and 2:2 electrolytes. The zeta-potentials estimated by the O’Brien and White (ξ_O-W) theory display a maximum and their values were lower than those calculated by the Dukhin and Semenikhin (ξ_D-S) theory, with which the maximum disappears. The considerations made by both theories about the contribution of all ions of the e.d.l. to the ionic conduction within this layer, is the reason for that differences.