Freezing as a path to build macroporous structures: Superfast responsive polyacrylamide hydrogels

Macroporous polyacrylamide (PAAm) hydrogels were prepared from acrylamide monomer and N,N'-methylene(bis)acrylamide (BAAm) crosslinker in frozen aqueous solutions. It was found that the swelling properties and the elastic behavior of the hydrogels drastically change at a get preparation temperature of -6 degrees C. The hydrogels prepared below -6 degrees C exhibit a heterogeneous morphology consisting of pores of sizes 10-70 mu m, while those formed at higher temperatures have a non-porous structure. PAAm networks with largest pores were obtained at -18 degrees C. The pore size of the networks increased while the thickness of the pore walls decreased by decreasing the monomer concentration. The hydrogels formed below -6 degrees C exhibit superfast swelling and deswelling properties as well as reversible swelling-deswelling cycles in water and in acetone, respectively. (c) 2006 Elsevier Ltd. All rights reserved.