Composition and property tunable ternary coacervate: branched polyethylenimine and a binary mixture of a strong and weak polyelectrolyte

Abstract

The formation of a composition- and property-tunable complex ternary coacervate was achieved by combining branched polyethylenimine (BPEI) and a binary mixture of polyacrylic acid (PAA) and poly(4-styrenesulfonic acid) (SPS). Presented here is a systematic study on how the ionic strength, stoichiometry, molecular weight and the presence of the cationic dye methylene blue (MB) can influence the composition and properties of the ternary coacervate. An increase in the ionization degree of PAA induced by increasing the ratio of BPEI to polyanion and by increasing the ionic strength leads to a higher incorporation of PAA into the coacervate. An increase in the molecular weight of PAA increases the proportion of SPS in the coacervate phase, likely due to reduced PAA chain mobility at high molecular weight. By introducing MB to the ternary polyelectrolyte system, the incorporation of SPS into ternary coacervate is significantly promoted, due to the interactions between MB and SPS such as π–π interactions that do not happen between MB and PAA. The hydrophobicity within the ternary coacervate is also significantly enhanced by the presence of accumulated MB. This study also shows that the ternary coacervate has promise as a material to stabilize solutes by efficiently inhibiting the complexation of solutes with transition metal ions such as copper ions. This might be applicable in retaining activity for enzymes that are sensitive to heavy metal ions. In addition, dynamic rheological measurements suggest that the rheological properties of the complex coacervates are tunable by varying polyanion composition as well as ionic strength, allowing for design of coacervates with a range of desired viscoelastic properties.