Electrophoretic mobility, primary electroviscous effect and colloid stability of highly charged polystyrene latexes

Abstract

Negatively charged polystyrene latexes with relatively high surface charge density have been prepared by the emulsifier-free method. Three samples of approximately the same particle size and different surface charge density have been obtained. The effect of pH and ionic strength on electrophoretic mobility has been studied and the experimental mobility converted into ζ-potential according to the O’Brien-White and Dukhin-Semenikhin theoretical treatments. — The ζ-potential values obtained by D-S equation are reasonably in agreement with the predictions of the Gouy-Chapman model. Thus, the passage of mobility and, correspondingly, ζ-potential through a maximum at low ionic strengths of the solution is due to the influence of surface conductance on electrophoresis. Also, primary electroviscous effect has been measured. An approximate equation derived from Booth theory explained the variation of the relative viscosity with the electrokinetic radius. The agreement between theory and experimental data was very good. Finally, critical coagulation concentration values were obtained experimentally. No significant differences were found, whcih is in agreement with the similar ζ-potential values obtained with the three samples of polystyrene latex.