Stimuli-responsive poly(N-isopropylacrylamide-co-sodium acrylate) hydrogels: A swelling study in surfactant and polymer solutions

Stimuli-responsive poly(N-isopropylacrylamide-co-sodium acrylate) [poly(NIPAM-co-SA)] hydrogel networks were prepared by aqueous free-radical copolymerization using the ammonium persulfate/N,N,N-1,N-1-tetramethylethylenediamine (APS/TMEDA) redox-pair initiator system in the presence of different amounts of N,N-1-methylenebisacrylamide (MBA) crosslinker. Higher swelling capacities were availed for these N-isopropylacrylamide-based hydrogels due to the presence of the hydrophilic poly(sodium acrylate) anionic units. In this the swelling phenomena of hydrogels in different surfactant and polymer solutions are investigated in a systematic way. The structural variation as well as the thermal stability of the surfactant-modified hydrogels were studied in detail. Further, the hydrogels swelling/diffusion kinetic parameters were investigated and a non-Fickian type of diffusion characteristics was found in all the swelling media for the diffusion of water into these hydrogels. (c) 2007 Elsevier Ltd. All rights reserved.