SWELLING EQUILIBRIA OF POLY(N-ISOPROPYLACRYLAMIDE) GEL IN AQUEOUS POLYMER-SOLUTIONS

Swelling equilibria of poly(N-isopropylacrylamide) (NIPA) gel in poly (ethylene glycol) (PEG)-water mixtures and the concentrations of PEG inside and outside the NIPA gel at 298.2K are discussed. NIPA gel exhibited continuous deswelling behavior for PEG6000, 20000, and 50000, a volume phase transition for PEG 1000, and reentrant behavior for PEG200. From the partition of PEG, it was found that the PEG molecules could not penetrate into the gel network in shrunk state. The gel absorbed low molecular weight PEGs but excluded high molecular weight PEGs in swollen state. A thermodynamic model, based on the Flory-Huggins theory coupled with the osmotic pressure by rubber elasticity proposed by Flory, was applied to correlate the swelling behavior of the gel in PEG-water mixtures.