(403c) Hybrid Field Theory and Particle Simulation Model of Polyelectrolyte–Surfactant Coacervation

Self-assembly and phase separation behavior of oppositely-charged surfactant-micelle and polyelectrolyte solutions 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 present a hybrid simulation / theory method for modelling coacervation in solutions of charged surfactants and oppositely charged homopolyelectrolytes, where the surfactants have self-assembled into worm-like micelles. Self-consistent field theory (SCFT) is used to model the polyelectrolytes in the solution, which interact with the surfactant-micelles through external potentials fields constructed from Monte Carlo (MC) simulations of the surfactant-micelles. The surfactant micelles are modeled using bead-rod MC simulations. In this work, solution phase diagrams are constructed, where molecular parameters such as the polyelectrolyte degree of polymerization and the strength of attraction between polymer and surfactant charges are varied and their effect on phase separation are evaluated. Additionally, the statistics of micelle bridging by the polyelectrolyte are evaluated for various macroion and salt ion densities. This hybrid MC / SCFT model can be generalized to study a variety of mixed macroionic systems and make predictions for phase separation behavior in relation to molecular structure.