Superfast responsive ionic hydrogels: Effect of the monomer concentration

A series of strong polyelectrolyte gels were prepared in aqueous solution, using the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) as the monomer and N,N'-methylene(bis)acrylamide (BAAm) as a crosslinker. The gels were both prepared below (-22 degrees C) and above (25 degrees C) the bulk freezing temperature of the water, producing cryogels and hydrogels, respectively. The crosslinker (BAAm) content was set at 17 mol%, while the initial monomer concentration C o was varied over a wide range. It was found that, at -22 degrees C, a macroscopic network starts to form at an initial monomer concentration of as low as 0.1 w/v%. In contrast to the conventional hydrogels formed at 25 degrees C, the cryogels have a discontinuous morphology consisting of polyhedral pores of sizes 10(0) -10(2) mu m. The cryogels exhibit superfast swelling properties, as well as reversible swelling-deswelling cycles in water and acetone. An increase in the initial monomer concentration from 2.5 to 10% further increases the response rate of the cryogels due to the simultaneous increase of the porosity of the networks.