Exploration of Phase Behavior in Asymmetric Semiflexible Polyelectrolyte Mixtures Using Polymer Field Theory

Polyelectrolyte phase segregation arises from the subtle effects of charge correlation, polymer structure, and mixing entropy. Predicting the conditions for phase transitions requires a theoretical approach that accurately reflects these thermodynamic contributions. Our self-consistent polyelectrolyte field-theoretic model includes explicit dipole-solvent ordering and employs the worm-like chain model within the random phase approximation to capture the fluctuation effects in polyelectrolyte solutions. In this work, we explore 3D theoretical phase diagrams that encompass all charge-neutral mixtures for various asymmetric polyelectrolyte solutions. Our theory is applied to these mixtures, focusing on the effects of 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 as a result of both associative and semi-segregative polymer-polymer phase separation. This work provides a comprehensive picture of the phase behavior in polyelectrolyte mixtures and offers fundamental insight into the thermodynamic driving forces that govern the predicted phase phenomena.