Ternary, Tunable Polyelectrolyte Complex Fluids Driven by Complex Coacervation

Complex coacervation was achieved by combining poly(allylamine) (PAR) or branched poly(ethylenimine) (PEI) with poly(acrylic acid) (PAA) and poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA). We systematically investigated the effects of stoichiometry, salt concentration, and pH. Ternary coacervates formed over a broader range of stoichiometries compared to the base PAA/PDMAEMA system. An enhanced resistance to salt, that is, resistance to dissolution of the complex with added salt, was observed for ternary coacervates. PEI-containing systems showed a considerable difference in salt resistance at pH 6-8 due to the dramatic change in charge density. This change was interpreted in the context of a theoretical treatment that relies on the Voorn-Overbeek model for free energy. Coacervate stability and viscoelastic behavior were affected by stoichiometry, salt, and pH. Ternary coacervates maintain the characteristics and tunability of typical binary coacervates, but the choice of the third component is important, as it significantly affects the response and material properties.