(59f) Modeling Swelling Equilibrium of Sodium Polyacrylate in Water and 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. Proper modeling phase behavior of hydrogels helps improving the performance of the superabsorbent products. The swelling behavior of sodium polyacrylate, a typical type of superabsorbent, has been investigated experimentally by Ogawa and Lee, etc. Maurer used a modified Pitzer model to describe swelling equilibrium; Sadowski extended PC-SAFT model with two additional interaction terms 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, swelling equilibrium between sodium polyacrylate hydrogel 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.

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