Revealing the Impact of Semiflexibility and Solvent Ordering on Polyelectrolyte Phase Phenomena Using Polymer Field Theory

Polyelectrolyte complex coacervation, an associative liquid-liquid phase separation, results in the coexistence of a polymer-rich (coacervate) and a polymer-lean (supernatant) phase. Understanding this phase separation is critical for applications in adhesives, drug delivery, and water purification. We explore 3D theoretical phase diagrams that capture all charge-neutral mixtures for various asymmetric polyelectrolyte solutions. We utilize our self-consistent polyelectrolyte field theory, which includes explicit dipole ordering and employs the wormlike chain model within the random phase approximation to capture the fluctuation effects of semiflexible chains. Our theory is applied to various asymmetric polyelectrolyte mixtures, focusing on the effects of different polymer length, charge, and structure between the two oppositely charged polymers within the solution as salt concentration and relative mixing fraction are varied. By exploring the complete domain space, we demonstrate the presence of both metastable binodal surfaces and critical points, as well as regions of three-phase coexistence due to both associative and semi-segregative polymer-polymer phase separation.