Swelling/deswelling kinetics of PNIPAAm hydrogels synthesized by microwave irradiation

This work involves the study of swelling and deswelling kinetics of poly(N-isopropylacrylamide) (PNIPAAm) hydrogels separately synthesized by means of microwave irradiation and normal water-bath heating. The swelling and deswelling kinetic curves of the PNIPAAm hydrogels were measured in water below and above the lower critical solution temperature (LCST), and their swelling and deswelling kinetic parameters were estimated. Textural properties and surface morphology of these PNIPAAm hydrogels were characterized by accelerated surface area and porosimetry apparatus and SEM. The effects of textural properties on their swelling and deswelling kinetic behavior were discussed. Results showed that swelling and deswelling rates of the synthesized PNIPAAm hydrogels increased with temperature, and the deswelling rates of these hydrogels were higher than their swelling rates. As compared with the PN hydrogel synthesized by the conventional method, the PM hydrogel synthesized by microwave irradiation had larger swelling and deswelling rate constants as well as lower swelling/deswelling activation energy due to its higher surface area and larger pore sizes, and thus it had faster response behavior.