ELECTROKINETIC CHARACTERIZATION OF HIGHLY SULFONATED POLYSTYRENE MODEL COLLOIDS

Highly sulfonated polystyrene latex particles were prepared by a two-stage "shot-growth" emulsion polymerization process in the absence of emulsifier. Sodium styrene sulfonate (NaSS) was used as an ionic co-monomer to produce a series of latex particles with nearly the same particle size but with different surface charge densities. The cleaning process used, including centrifugation and redispersion with the aid of strong sonication, proved to exert a strong influence on the final surface charge density of the particles. The electrokinetic behavior of three latex samples with surface charge densities between 13.9 and 19.4-mu-C cm-2 was very similar, with constant values of the electrophoretic mobilities for pH between 4 and 11 and a maximum in the electrophoretic mobility values when the ionic strength was 5.10(-2) M NaCl. This last result was found even after a systematic and long latex cleaning process, and after treatment at high electrolyte concentrations. The experimental results for the electrokinetic characterization of these highly sulfonated polystyrene latexes suggest that the surface of the particles are covered by a layer of oligomers or polymer chains which are chemically bound to the surface, and which control the colloidal properties of this type of latex.