Ionic-group-dependent phase behavior of polyelectrolyte coacervates

Complex coacervates are polymer-rich phases generated by liquid-liquid phase separation when oppositely charged polyelectrolytes are mixed in aqueous solutions. Since the previous Voorn-Overbeek model does not account for the chain connectivity and chemistry-specific details, advanced models have been suggested up to now. However, experimental data of well-defined model system is rare to compare with the theoretical description. In this study, 4 polyelectrolytes are prepared (e.g., strong/weak and polyanion/polycation) from identical parent polymer using anionic polymerization, and thus 4 pairs of polyelectrolyte complex coacervates are investigated to map out the phase diagrams as a function of the pair of ionic group. It is found that the phase diagram shows distinctive features including salt resistance, the area of a two-phase region and the shape of binodal curves depending on the pairs of polyelectrolytes. In addition, atomistic MD simulations give molecular-level insight into the interaction of two charged moieties and especially show a clear difference in the ability to form hydrogen bonds. We believe chemistry specific parameters play an important role in control phase behavior and these findings shed new light on the biologically important topic of complex coacervation.