Colloidal Stabilization of Polystyrene Particles by Adsorption of Nonionic Surfactant: II. Electrosteric Stability Studies

Abstract

An investigation into the effects of interfacial properties on the colloidal stability of monodisperse polymer colloids using two sulfate polystyrene latexes is presented. 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, using the DLVO theory, is much lower than the theoretical value given by the Lifshitz theory. In order to achieve good agreement between the experimental and theoreticalAvalues, different corrections to the DLVO theory were introduced as the hydrodynamic effect and the size of the hydrated ions. When the nonionic surfactants Triton X-100, Triton X-165, Triton X-305, and Triton X-405 were adsorbed onto both latexes a new correction was made to the DLVO theory: the effect of electrosteric stabilization. Including the elastic–steric effect and the osmotic potential, five parameters are involved in the total interaction energy. By using well-known latexes and surfactants, three of them can be fixed. The thickness of the hydrophilic polymer chains was estimated by the Eversole and Boardman equation, while the effective volume fraction of segments in the external layer was used as the fitting parameter. The quantitative results about electrosteric stabilization obtained using this theory can be explained as a consequence of the conformation of the surfactant on the latex surface via the values of the volume fraction of segment in the external regions.