The Impact of Electrolyte on the Aggregation of the Complexes of Hyperbranched Poly(ethyleneimine) and Sodium Dodecyl Sulfate

Abstract

The aggregation of the negatively charged complexes of hyperbranched poly(ethylenimine) (PEI) and sodium dodecyl sulfate (SDS) has been investigated at different sodium chloride (NaCl) concentrations using coagulation kinetics, electrophoretic mobility and dynamic light scattering measurements. The observed variation of the initial rate of coagulation with NaCl concentration indicates the formation of kinetically stable colloid dispersions in the investigated composition and pH range. These dispersions are electrostatically stabilized due to the adsorption of excess dodecyl sulfate ions on the surface of the polyelectrolyte/surfactant particles. Because of the enhanced adsorption of the anionic surfactant, the kinetic stability of the PEI/SDS dispersions increases with increasing SDS concentration and decreasing pH. Finally, we rationalize the effect of salt on the phase behavior and surface properties of polyelectrolyte/surfactant mixtures in terms of the salt-induced aggregation features of polyelectrolyte/surfactant particles.