Electrokinetic potential of polystyrene particles in polyelectrolyte and polyelectrolyte mixtures solutions

Abstract

The effect of three samples of SNF FO grade cationic polyelectrolyte (PE) and two samples of SNF AN grade anionic polyelectrolyte as well as their binary mixtures on the electrokinetic potential of monodisperse carboxylated polystyrene (PS) particles as a function of the contact time of polymer solution with particles, the polyelectrolyte/mixture dose, its composition, the charge density (CD) of polymers and sequence of their adding to the suspension has been studied. Also the effect of pH and KCl concentration on the ζ-potential of “bare” and polymer-covered PS particles have been measured. It has been shown that addition of increasing amount of anionic polyelectrolytes increases the absolute value of the negative zeta-potential of PS particles; this increase is stronger the charge density of the polyelectrolyte and pH of the system are higher. Adsorption of cationic polyelectrolytes leads to a significant decrease in the negative ζ-potential and to overcharging the particles; changes in the ζ-potential are more pronounced for PE samples with higher CD and for suspensions with lower pH values. In mixtures of cationic and anionic PE, in a wide range of mixtures composition, the ζ-potential of particles is determined by the adsorbed amount of the anionic polymer independently of the CD of polyelectrolytes and the sequence of addition of the mixture components. The isoelectric point of the surface is reached at the adsorbed amount of positive charges that is approximately equal to the surface charge density of particles. The laws observed were explained by features of macromolecules conformation in adsorbed mixed polyelectrolyte layers. Considerations about the role of coulombic and non-coulombic forces in the mechanism of anionic/cationic polyelectrolyte adsorption are presented.