Abstract
This paper describes the formation of soft nanoparticles resulting from electrostatically driven complexation of oppositely charged polyelectrolytes. The system was composed of a strong polyanion (polystyrene sulfonate, PSS) and a weak polycation (poly(allylamine) hydrochloride, PAH) in large excess. Soft nanoparticles were obtained by pouring a PSS solution into a PAH one under constant stirring. The polyelectrolyte complexes (PEC) were characterized through a viscometric study complemented by Dynamic Light Scattering (DLS), electrophoretic mobility and suspension turbidity measurements. PEC suspensions were centrifuged and by measuring the viscosity of the supernatant, we were able to estimate the free polycation concentration and hence the percentage of complexed polycation. We also measured the relative viscosity of the suspensions; from the estimated contribution of the PEC particles and of the polycation in excess, the average particle volume fraction was estimated. From all viscometric data, we could derive the evolution of the binding stoichiometry in PEC and of the effective particle volume fraction as a function of the mixing ratio (ratio of the cationic to anionic groups) and of the pH. Our results emphasize the importance of charge accessibility in controlling both the stoichiometry and packing density of the complexes.
Highlights
When solutions of two oppositely charged polymer chains are mixed, PolyElectrolyte Complexes (PEC) are formed spontaneously
To contribute to a better understanding of the mechanism of PEC formation, of the influence of charge density on PEC formation, we studied in the present work the structural changes during complex formation between Poly(StyreneSulfonate) (PSS) and Poly(Allylamine) Hydrochloride (PAH)
Since PAH macromolecules are in large excess, it is likely that only a fraction of them is involved in the complexation process
Summary
When solutions of two oppositely charged polymer chains are mixed, PolyElectrolyte Complexes (PEC) are formed spontaneously. PEC can be composed of natural and/or synthetic polyions, charged surfactants, etc They are widely used in various fields such as water treatments, coatings, paper industry, drug delivery and gene therapy. Water-soluble polyelectrolyte complexes are formed with polyelectrolytes having a weak charge density and large differences in molecular dimensions when they are mixed in non-stoichiometric ratios (Dautzenberg and Karibyants, 1999; Kabanov and Zezin, 1984). Polyions having a high charge density and/or similar high molar masses lead to insoluble and highly aggregated complexes, according to the scrambled-egg model, by the incorporation of several polyelectrolyte chains (Dautzenberg et al, 1996; Thunemann et al, 2004). Colloidal dispersions in the submicrometer range can be obtained by polyelectrolyte complexation, provided polymer concentrations remain low
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