Models for Complexation and Coacervation in Charged Macromolecules

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. 

In this talk, I will first show how we are modeling complex coacervation between two linear, flexible polymers. Even simple theories that account for charge correlations can reproduce experimental observations, and can provide predictions for phase behavior and pH effects. We then will show how we build on this method, and use 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 we map out the phase behavior of these polyelectrolyte-surfactant micelle coacervates upon varying the strength of these correlations, the polyelectrolyte chain length, and micelle size surface charge density. 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 micelle excluded volume. We also elaborate on the nature of these charge correlations, and study how micelle charge fraction and polyelectrolyte sequence affects micelle-micelle interactions.