Charge-Driven Phase Behavior of Particle-Polyelectrolyte Coacervates

Oppositely-charged macromolecular species can undergo an associative phase separation, in a process known as complex coacervation. There has been significant interest in coacervation between two polyelectrolytes, however for many biological and industrial applications coacervation occurs between species where at least one of the components is not a linear polymer. This includes coacervates driven by charged proteins, colloids, or surfactant micelles.

We have developed a hybrid simulation and field theory calculation to capture the physics of liquid-liquid phase separation in polymer-surfactant micelle coacervates. We demonstrate the importance of charge correlations between strongly-charged micellar surfaces, and use molecular simulation to make predictions for the strength and form of this interaction. These results allow us to map out the phase behavior of these polyelectrolyte-surfactant micelle coacervates upon varying parameters such as the micelle surface charge density, the polyelectrolyte chain length, and the role of steric repulsions between micelles. We show qualitative agreement with experimental collaborators, and show that a coexistence exists between micelle-dilute and micelle-dense phases reflects a competition between charge correlations and excluded volume. We also elaborate on the nature of these charge correlations, and study how polyelectrolyte sequence affects micelle-micelle interactions.