Microstructure, mechanical and swelling properties of microgel composite hydrogels with high microgel content and a microgel cluster crosslinker

Acrylamide-co-2-acrylamido-2-methylpropane sulfonic acid based microgel composite (MC) hydrogels with high microgel content were prepared by post crosslinking method. Acetone was used as a demulsifier and in one group of mixed solvents, which reduced the foam during nitrogen bubbling. When the microgel content was high, the microgel particles containing hydroxymethyl groups aggregated to cluster. Acetone increased the homogeneity of cluster dispersing. The microgel composite hydrogel with high microgel content was crosslinked by a cluster, which had high mechanical strength and swelling rate. Although the tensile strength and elongation decreased as the microgel content increased, the swelling rate, the size and the number of pores increased as the microgel content increased. The exciting result was that the composite hydrogel with microgel content of 12 had a porous structure. Even though it had a high crosslinking density, the hydrogel was elastic and had excellent properties. It had a tensile strength of 44 kPa and an elongation of 45% when the water content was 90%, which is considerably higher than the conventional hydrogel. It can reach swelling equilibrium in 5 hours for 3 mm(3) sizes of samples, which was faster than the conventional hydrogel owing to the partly connected porous structure. These excellent properties were due to the unique structure where the hydrogel was crosslinked by a microgel cluster. It may become a new method of preparing hydrogels with a porous structure.