Effects of monovalent and multivalent ions on the stability of a polyelectrolyte complex with entrapped surfactants

In this article, we report the effects of nine different monovalent and multivalent salts on the particle size and stability of refined, positively charged polyelectrolyte complexes (PECs) with entrapped surfactant. Dynamic light scattering and ζ potential measurements of these polymeric particles as a function of various salt concentrations showed that both counter ions and co‐ions induced a concentration‐dependent increase in the particle size and a decrease in the ζ potential. We found that the anion concentration where the particle size doubled and the maximum anion concentration beyond which particle precipitation occurred (C_a,max) demonstrated a power law dependence on the anion valence. Moreover, for anions of the same valence but different hydration radio, C_a,max decreased in the following order: NO₃ → Cl → HPO₄^2? > SO₄^2? > PO₄^3?. However, unlike the case of hard colloids where co‐ions have relatively little effect on particle interactions, the co‐ions also increased the hydrodynamic radii of our PECs in the following order: K⁺ ≈ Na⁺ > Ca²⁺ > Mg²⁺ > Al³⁺. Furthermore, we found that the entrapped surfactants were shielded from the adverse effect of multivalent ions; this established that the monovalent and multivalent ions interacted with the polyelectrolyte shells of the PEC. This behavior was in contrast with the effect of salts on mixtures containing the polyelectrolyte and surfactant components, where the addition of salts typically causes an interaction with the individual components. Because several biomedical and technological applications involving PECs require saline environments, our studies provide insight into how small ions influence the PEC stability in applications involving varying salinities. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42099.