The importance of the mixing energy in ionized superabsorbent polymer swelling models

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Abstract

The Flory-Rehner theoretical description of the free energy in a hydrogel swellingmodel can be broken into two swelling components: the mixing energy and the ionic energy. Conventionally for ionized gels, the ionic energy is characterized as themain contributor to swelling and, therefore, themixing energy is assumed negligible. However, this assumption ismade at the equilibrium state and ignores the dynamics of gel swelling. Here, the influence of themixing energy on swelling ionized gels is quantified through numerical simulations on sodium polyacrylate using aMixed Hybrid Finite ElementMethod. For univalent and divalent solutions, at initial porosities greater than 0.90, the contribution of themixing energy is negligible. However, at initial porosities less than 0.90, the total swelling pressure is significantly influenced by the mixing energy. Therefore, both ionic and mixing energies are required for the modeling of sodium polyacrylate ionized gel swelling. The numerical model results are in good agreement with the analytical solution as well as experimental swelling tests.

Original languageEnglish
Article number609
JournalPolymers
Volume12
Issue number3
DOIs
Publication statusPublished - 1 Mar 2020

Keywords

  • Finite deformation
  • Flory-Huggins equation
  • Flory-Rehner theory
  • Ionized hydrogels
  • Mixing energy
  • Polymer mechanics
  • Sodium polyacrylate
  • Superabsorbent polymer
  • Swelling

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