Equilibrium swelling of N-isopropyl acrylamide based ionic hydrogels in aqueous solutions of organic solvents: Comparison of experiment with theory

A series of polyelectrolyte hydrogels were synthesized by copolymerization of N-isopropyl acrylamide with the ionic monomer sodium methacrylate. The swelling behavior and the effect of electric charge on the composition-induced collapse of the resulting ionic hydrogels were investigated in aqueous solutions of five single organic solvents (acetone, ethanol, acetic acid, butanol and methyl isobutyl ketone) at 298 K. The experimental results of some hydrogels were correlated applying a thermodynamic model, which combines an expression for the Gibbs energy of a liquid phase with an equation for the Helmholtz energy of an elastic network. The model was also successfully used to predict the swelling equilibrium of the other hydrogels in aqueous, organic solutions.