COLLOID STABILITY AND ELECTROKINETIC CHARACTERIZATION OF POLYMER COLLOIDS PREPARED BY DIFFERENT METHODS

The electrokinetic characterization and colloidal stability of functio nalized latexes, two sulfonated polystyrene model colloids prepared by different methods, are described. JM1 latex was synthesized by an emu lsion copolymerization process from styrene and sodium styrene sulfona te (NaSS) in the absence of an emulsifier. SN9 latex was prepared by a two-stage ''shot-growth'' emulsion polymerization process without emu lsifier and using NaSS as an ionic comonomer. The two latexes had near ly the same particle size but very different surface charge densities. When the electrophoretic mobility of these functionalized model collo ids was studied as a function of pH and ionic strength, the latex with the lower surface charge yielded higher mobility values. The experime ntal results for the electrokinetic characterization suggest that the surface of the particles prepared with a second injection is covered b y a layer of oligomers or polymer chains which shift the shear plane t owards the bulk solution, increasing the anomalous surface conductance of the particle-electrolyte solution interface. The stability factor and the critical coagulation concentration were studied for the two sa mples. Better colloidal stability was observed for the latex prepared with the second injection, which has a higher surface charge density. There is an important electrostatic contribution to the stability, but there also seems to be a steric contribution due to the structure of the electric double layer which surrounds the particles. (C) 1997 Else vier Science B.V.