Abstract: Based on the phase equilibrium conditions for systems containing gels given by Maurer and Prausnitz, a model to correlate and predict the swelling behaviors of hydrogels in aqueous organic solutions is proposed. In the model, gel is considered as a combination of a shell of an elastic semipermeable membrane and a core of a fluid phase. The fluid core consists of only the network building materials and other components that are able to partition in gel phase and surrounding coexisting liquid phase, and is enveloped by the membrane shell. The excess Gibbs energies of the gel phase and the surrounding coexisting fluid phase are calculated using UNIQUAC equation, the elastic properties of polymer network are described by the “phantom network” theory, and the additional differences in the size of the species are taken into account by “free-volume” contribution. To test the model, a series of N-isopropylacrylamide gels, using N,N’-methylene diacrylamide as the crosslinker, are synthesized by free radical polymerization under nitrogen atmosphere. The swelling experiments are conducted in aqueous solution of acetone at 25 ℃. The results show that the increases of swelling capacity of the gels with decreasing amount of crosslinker and total mass fraction of polymerizable materials predicted by the model are in good agreement with the experimental data. Moreover, the model also predicts no difference of acetone concentration in the gel phase and the coexisting liquid phase, as long as the gel is in a swollen state. However, in the region where the swelling degree of the gel is rather small there is a small enrichment of acetone in the gel phase. All these show the potential of the model to correlate and predict the swelling behaviors of hydrogels in aqueous organic solutions.

Key words: Correlation/prediction, Hydrogel, N-isopropylacrylamide(IPAAm), Acetone