(59g) Thermodynamic Modeling of Aqueous Multivalent Polyelectrolyte Systems with Polyelectrolyte NRTL Model

Polyelectrolytes are a type of commonly seen polymers both in human body and in industry. Some examples are DNA and RNA in living cells, selective permeable membranes, and ion-exchange resins. Specific features of polyelectrolytes such as hydrophilic and hydrophobic segments along the polymer backbone endow these molecules with unique and intriguing behaviors.

A recent study reports a novel polyelectrolyte NRTL model for thermodynamic modeling of aqueous monovalent polyelectrolytes [1]. The model expresses the excess Gibbs energy of the polyelectrolyte solutions as the sum of two terms: long-range interaction term and short-range interaction term. The long-range interaction term accounts for the charged polyion segment-ion and ion-ion interactions with the Pitzer-Debye-Hückel limiting law [2] and the polyion backbone-ion interactions with the Manning limiting law [3]. The short-range interactions, including molecule-molecule, molecule-ion/polyion and ion/polyion-ion/polyion interactions, are treated with the electrolyte non-random two-liquid (eNRTL) equation [4]. With use of binary interaction parameters, the model has been shown to successfully correlate experimental data of various colligate properties, such as osmotic coefficients of the polyelectrolyte solutions, activity coefficients of counterions, and mean ionic activity coefficients of added salts, for aqueous monovalent polyelectrolyte solution [1]. In this study, we review literature thermodynamic data for aqueous divalent and multivalent polyelectrolytes and highlight the differences from monovalent ones. We further examine the polyelectrolyte NRTL model behavior for aqueous multivalent polyelectrolyte systems and show successful correlations of experimental activity coefficient data for multivalent counterions and added salts, and osmotic coefficient data for multivalent polyelectrolyte solutions. Future studies should involve extension of the polyelectrolyte NRTL model for aqueous mixed polyelectrolyte solutions.

Reference:

[1] Yu, Y., Hossain, N., Chen, C.-C. Modeling of Polyelectrolytes System with Electrolyte Nonrandom Two Liquid Model. AIChE Journal. In preparation.

[2] Pitzer, K. S. Thermodynamics of Electrolyte. I. Theoretical Basis and General Equations. The Journal of Physical Chemistry. 77 (1973) 268-277.

[3] Manning G. S. Limiting Laws and Counterion Condensation in Polyelectrolyte Solutions I. Colligative Properties. The Journal of Chemical Physics. 51 (1969) 924-933.

[4] Song, Y., Chen, C.-C. Symmetric Electrolyte Nonrandom Two-Liquid Activity Coefficient Model. Industrial & Engineering Chemistry Research. 48 (2009) 7788-7797.