The effect of salt on the association between linear cationic polyelectrolytes and sodium dodecyl sulfate

Abstract

The aggregation of polyelectrolyte–surfactant particles has been investigated at large excess of the surfactant in the presence of NaCl using coagulation kinetics, electrophoretic mobility and dynamic light scattering measurements. The investigated systems were mixtures of sodium dodecyl sulfate (SDS) with poly(vinylamine) (PVAm) as well as with poly(diallyldimethylammonium chloride) (PDAC). The observed variation of the initial rate of coagulation with NaCl concentration of PVAm–SDS and PDAC–SDS particles is in qualitative agreement with the predictions of DLVO theory. This finding provides evidence for the formation of electrostatically stabilized colloid dispersions in the investigated composition range of these mixtures. The kinetic stability of these dispersions increases with increasing SDS concentration and polyelectrolyte charge. The colloid dispersion nature of polyelectrolyte–surfactant mixtures has important consequences with respect to the surface and phase behaviour of these systems in the presence of supporting electrolyte.