Stabilization Mechanism of Colloidal Suspensions by Gum Tragacanth: The Influence of pH on Stability

An acidic polyelectrolyte, gum tragacanth (GT) , was found to stabilize polystyrene latex particles due to a steric stabilization mechanism. The stability depends significantly on the pH of the solution. To elucidate the stabilization mechanism, a number of parameters, such as the adsorption isotherm, the zeta potential, and the conformation were measured as a function of pH. The adsorption isotherms showed that pH has little effect on the amoun t of GT adsorbed on the surface. Photon correlation spectroscopy studies showed that the steric layer thickness increases as pH decreases, demonstrat ing that the pH dependence of stability is attributed to the conformational change of GT with pH. Finally, the degree of dissociation of carboxyl groups of GT molecules (i.e., pH) has a significant effect on the flocculation behavior of latex particles and can be modulated to bring about spontaneous deflocculation of latex particles. © 1988 Academic Press, Inc.