COLLOIDAL STABILITY OF POLYMER COLLOIDS WITH DIFFERENT INTERFACIAL PROPERTIES - MECHANISMS

An investigation is presented into the effects of interfacial properti es on the colloidal stability of monodisperse polymer colloids using a sulfonate polystyrene (PS) and a styrene-hydroxyethyl methacrylate co polymer (PSHEMA) latex, Both latexes were prepared by emulsion copolym erization in the absence of surfactant, The experimental stability of these colloidal dispersions was studied in relation to the concentrati on (C-e) of an indifferent electrolyte, Results are compared to curren t models, relating the stability ratio (W) to intermolecular forces be tween particles. The Hamaker constant (A) obtained from the log W-log C-e plots 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 theoretical A values, different corrections to t he DLVO theory were introduced. First, the modified stability factor ( W) was numerically estimated taking into account the hydrodynamic effe ct as given by L. A. Spielman [J. Colloid Interface Sci. 33, 562 (1970 )]., Next, the real size of the hydrated ions was also considered, Wit h these modifications only, small discrepancies remained between the t heoretical and experimental values of the Hamaker constant in the case of the PS latex; however, the A value obtained for the PSHEMA latex s tudied is rather low, As HEMA is a nonionic and polar monomer, a new c orrection was made to the DLVO theory: the effect of electrosteric sta bilization, Both steric repulsion and the electrostatic effect are sho wn to play a significant role in maintaining dispersion stability for the PSHEMA latex. (C) 1996 Academic Press, Inc.