(60dg) Modeling Swelling Equilibrium of Sodium Acrylate and Sodium 2-Acrylamido-2-Methylpropanesulfonate Copolymereric Hydrogels in Saline Water with Polyelectrolyte Non-Random Two Liquid Model

Superabsorbent polymers or hydrogels are widely used in daily hygiene product as well as multiple industrial applications. The swelling behavior of a typical type of superabsorbent, sodium polyacrylate (SA) with and without sodium 2-acrylamido-2-methylpropanesulfonate (NaAMPS) as copolymer, was investigated experimentally by Ogawa [1] and Lee, etc [2]. Maurer used a modified Pitzer model to describe swelling equilibrium [3]; Sadowski extended PC-SAFT model with two additional interaction terms [4] to calculate VLE and water activity of polyelectrolyte hydrogels. Both models require extensive number of adjustable parameters and have limitation on description of speciation in the hydrogel phase.

Based on our recently developed electrolyte non-random two liquid model [5], swelling equilibrium between the copolymeric hydrogels of SA-NaAMPS and saline water of different concentrations has been analyzed. Phase equilibrium is modeled according to equal chemical potential of mobile ion components with a correction factor to account for the elastic network of the polymer. The speciation and activity coefficients of mobile ions in hydrogels can be found with this thermodynamic framework for the first time. Model prediction for degree of absorption is in good agreement with available data.

[1] Ogawa, I., Yamano, H., & Miyagawa, K. (1993). Rate of swelling of sodium polyacrylate. Journal of applied polymer science, 47(2), 217-222.

[2] Superabsorbent polymeric material. V. Synthesis and swelling behavior of sodium acrylate and sodium 2‐acrylamido‐2‐methylpropanesulfonate copolymeric gels. Journal of applied polymer science, 69(2), 229-237.

[3] Thiel, J., & Maurer, G. (1999). Swelling equilibrium of poly (acrylamide) gels in aqueous salt and polymer solutions. Fluid phase equilibria, 165(2), 225-260.

[4] Arndt, M. C., & Sadowski, G. (2014). Thermodynamic model for polyelectrolyte hydrogels. The Journal of Physical Chemistry B, 118(35), 10534-10542.

[5] Yu, Yue, Li, Yuan, Hossain, Nazir, Chen, Chau-Chyun, Chen, (2019). Nonrandom Two-Liquid Activity Coefficient Model for Aqueous Polyelectrolyte Solutions. Fluid Phase Equilibria, 497, 1-9.