Colloidal Stability of Polymer Colloids with Different Interfacial Properties: Mechanisms

Abstract

An investigation is presented into the effects of interfacial properties on the colloidal stability of monodisperse polymer colloids using a sulfonate polystyrene (PS) and a styrene–hydroxyethyl methacrylate copolymer (PSHEMA) latex. Both latexes were prepared by emulsion copolymerization in the absence of surfactant. The experimental stability of these colloidal dispersions was studied in relation to the concentration (Ce) of an indifferent electrolyte. Results are compared to current models, relating the stability ratio (W) to intermolecular forces between particles. The Hamaker constant (A) obtained from the logW–logCeplots and using the DLVO theory is much lower than the theoretical value given by the Lifshitz theory. To achieve good agreement between the experimental and theoreticalAvalues, different corrections to the DLVO theory were introduced. First, the modified stability factor (W) was numerically estimated taking into account the hydrodynamic effect as given by L.A. Spielman [J. Colloid Interface Sci.33,562 (1970)]. Next, the real size of the hydrated ions was also considered. With these modifications only, small discrepancies remained between the theoretical and experimental values of the Hamaker constant in the case of the PS latex; however, theAvalue obtained for the PSHEMA latex studied is rather low. As HEMA is a nonionic and polar monomer, a new correction was made to the DLVO theory: the effect of electrosteric stabilization. Both steric repulsion and the electrostatic effect are shown to play a significant role in maintaining dispersion stability for the PSHEMA latex.