Fast responsive poly(N, N-diethylacrylamide) hydrogels with interconnected microspheres and bi-continuous structures

We prepared thermo-responsive polymer hydrogels by gamma-ray irradiation of aqueous solutions of N, N-diethylacrylamide at different temperatures below and above its lower critical solution temperature (LCST). Poly(N, N-diethylacrylamide) gel had a transparent and homogeneous structure when the radiation-induced polymerization and crosslinking were carried out below the LCST (25 A degrees C) of the polymer. On the other hand, cloudy and heterogeneous gels were formed at temperatures above the LCST of the polymer (> 35 A degrees C). From environmental scanning electron microscopy observations, the gels prepared at 35 and 40 A degrees C were seen to show sponge-like bi-continuous porous structures, while those prepared at 50 A degrees C showed a porous structure consisting of interconnected microspheres. For temperature changes between 10 and 40 A degrees C, gels with porous structures showed rapid volume transitions on a time scale of about a minute, not only for shrinking but also for swelling processes, which is in remarkable contrast to the porous poly(N-isopropylacrylamide) hydrogels.