Field Theory Description of Polyelectrolyte-Surfactant Coacervate Phase Behavior*

Interactions between polyelectrolytes and oppositely-charged surfactant-micelles can lead to a charge-driven liquid-liquid phase separation known as complex coacervation. These systems and their phase behavior have been studied for variety of applications including food products, personal hygiene products, and pharmaceuticals. In this work we present a field theoretic calculation(1) for modeling phase separation in charged polymer and surfactant solutions, where we treat micelle surface sites as permanent sites interacting with polymer density fields. Monte Carlo simulations of the surfactant micelle conformations determine the micelle surface site distributions, and we can subsequently evaluate the system free energy for phase diagram calculations. We treat the system as a three-component system comprised of polymer-micelle complexes, polymer-salt complexes, and solvent; the resulting ternary phase diagrams for the system can be compared to experimental results in the literature, and we can probe a number of molecular features including polymer distribution and bridging in the coacervate phase.
1 G. Fredrickson,The Equilibrium Theory Of Inhomogeneous Polymers (OUP Oxford, Oxford, 2005).