Modelling Coacervation in Polyelectrolyte – Surfactant Micelle Solutions

Self-assembly and solution behavior of oppositely-charged surfactant-micelles and polyelectrolytes have been studied for a variety of applications including pharmaceuticals and personal care products, as well as for understanding biomolecular condensates with significantly charged constituent molecules. These systems have been shown to undergo complex-coacervation, which is a liquid-liquid phase separation in solutions of oppositely-charged macromolecules. This phase separation results in a coacervate phase that is rich in charged macromolecules and the supernatant which is poor in charged macromolecules. The disparities in length scales and strong Coulombic interactions in these mixed macroion solutions can make modeling these systems computationally challenging. In this work, we use self-consistent field theory (SCFT) to model the thermodynamics of solutions containing worm-like surfactant-micelles interacting with oppositely-charged homopolyelectrolytes. The SCFT simulations are informed by Monte Carlo (MC) simulations of the surfactant-micelles as hard-sphere chains. In this work we show that local charge-charge correlations are a key component to phase separation in these systems. The hybrid SCFT / MC model presented can be further generalized to apply to other mixed macroion systems.