pePC-SAFT: Modeling of polyelectrolyte systems: 1. Vapor–liquid equilibria

A molecular thermodynamic model for polyelectrolyte systems—called pePC-SAFT—is proposed. The effect of charged monomers within the polyelectrolyte chain is explicitly taken into account in the reference term by replacing the hard-chain contribution of the PC-SAFT model by a charged-hard-chain contribution. Moreover, counterion condensation is accounted for to determine the effective number of charges along the polyion as well as of free counterions. The electrostatic contribution of the free counterions is described by a Debye–Hückel term. AFT is applied to model the phase equilibria of aqueous solutions of poly(sodium acrylate) and poly(ammonium acrylate) with and without added NaCl as function of temperature, salt concentration as well as molar mass and degree of neutralization of the polyelectrolytes. For the modelling, the pure-component parameters of the polyelectrolyte as well as the binary interaction parameter between water and the polyion were used as determined for the non-charged polymers. Using only the information of the polyelectrolyte degree of neutralization and without fitting additional parameters, the model is able to predict the vapor–liquid equilibria of polyelectrolyte systems in satisfactory agreement with experimental data.