The Structure of Polyelectrolyte Complex Coacervates and Multilayers

The equilibrium structure of the polyelectrolyte (PE) complex coacervates and homogeneous multilayers formed by polycations and polyanions with incompatible backbones in a poor solvent is studied using a mean-field approach. The state diagrams involving symmetric and asymmetric homogeneous phases are obtained in terms of interaction parameters, ionic strength, and composition. It is found that interfacial tension between two coexisting uniform PE phases vanishes at a certain line, where both phases remain stable and (unlike the classical critical behavior) highly distinct in composition and charge. It is also shown that a microdomain structure of the coacervate phase gets thermodynamically stable at low enough salinity. Lamellar structures arising in symmetric coacervates are investigated in all segregation regimes (weak, strong, and intermediate). The mechanism of an exponential growth of uniform multilayer thickness upon layer-by-layer deposition is elucidated. It is predicted that the exponential growth rate increases with the solution ionic strength in agreement with experimental data.

Automated summary

The study investigates the equilibrium structure of polyelectrolyte (PE) complex coacervates and homogeneous multilayers formed by polycations and polyanions in a poor solvent using a mean-field approach. It is found that interfacial tension between coexisting uniform PE phases vanishes at a certain line, allowing both phases to remain stable with distinct compositions and charges. The exponential growth rate of uniform multilayer thickness is predicted to increase with solution ionic strength.