Swelling of N-isopropyl acrylamide hydrogels in aqueous solutions of poly(ethylene glycol)

Hydrogels are three-dimensional networks of hydrophilic polymer chains with properties between liquids and solids. One of the most interesting features is their capability to absorb liquids. This feature is called swelling. The amount of absorbed substances depends on the structure of the gel and the composition of the coexisting liquid phase. This paper reports experimental investigations of the swelling behavior of non-ionic, synthetic hydrogels of N-isopropyl acrylamide. The swelling equilibrium of two hydrogels in aqueous solutions of poly(ethylene glycol) with different average molecular weights was investigated at 298 K. uilibrium properties and the compositions of the coexisting phases (gel phase and surrounding liquid solution) are correlated/predicted with a thermodynamic model which combines an expression for the Gibbs energy of a liquid with an expression for the Helmholtz energy of an elastic network.