Reentrant-Convex Swelling of Thermoresponsive Gels in Mixtures of Solvents

Design of organohydrogels with exceptional physical properties requires simple and reliable models for swelling of polymer networks in mixtures of water with organic solvents. A model is developed for equilibrium solvent uptake by thermoresponsive gels in binary mixtures that involves a relatively small number of adjustable parameters and describes various types of swelling diagrams (monotonically decreasing, with points of minimum, and with several maxima and minima) in a unified manner. Its ability to describe (and to predict qualitatively) equilibrium swelling curves is confirmed by fitting experimental data on poly(N-isopropylacrylamide), poly(N,N-dimethylacrylamide), poly(acryloyl-L-proline methyl ester), and poly(acrylamide) gels in mixtures of water with acetone, acetonitrile, dioxane, dimethyl sulfoxide, ethanol, methanol, N-methylpyrrolidone, 1-propanol, and tetrahydrofuran.