Molecular thermodynamics of complex coacervate systems. Part I: Modeling of polyelectrolyte solutions using pePC-SAFT

Rigorous molecular modeling of polyelectrolyte solutions is complicated by several intrinsic challenges of those systems, such as the strong charge correlation and the complex cocktail of short-range and long-range interactions, which span over a broad length scale. On the other hand, there is an increasing interest in understanding and designing polyelectrolyte systems in biology, life science, medicine, and (bio)chemical engineering. Thermodynamics of polyelectrolyte solutions is rather underexplored, and the difficulties in describing polyelectrolytes at the molecular level as well as the lack and the uncertainty of experimental data might have hindered the development of accurate thermodynamic models for polyelectrolytes. In this work, the main phenomena of counterion condensation, complex formation and coacervate formation are discussed and considered for the further development of polyelectrolyte PC-SAFT (pePC-SAFT) as modeling framework in this work. The new development was then validated using experimental osmotic coefficients of aqueous polyelectrolyte solutions. Finally, liquid-liquid phase separation (LLPS) of complex coacervate systems (aqueous solutions containing oppositely charged polyions) were modeled with pePC-SAFT, and the results were in very good agreement with literature data.