Preparation and characterization of dual-sensitive double network hydrogels with clay as a physical crosslinker

pH- and temperature-responsive double network (DN) hydrogels were prepared by using poly (N-isopropylacrylamide) (PNIPAM) as a tightly crosslinked 1st network, polyacrylic acid (PAA) as a loosely crosslinked 2nd network and Laponite as a crosslinker. The synergetic effects of Laponite as crosslinker and DN structure on various physical properties were investigated. The structure and morphology of the nano-composite hydrogels were characterized by SEM and FTIR, while temperature-sensitivity was investigated with DSC and TGA. The swelling/deswelling behaviors and mechanical properties of the DN hydrogels were compared with that of the corresponding chemically cross-linked hydrogel. The results showed that the DN hydrogels had much greater equilibrium-swelling ratio, much faster response rate and significantly improved mechanical properties. Moreover, the swelling ratios of DN hydrogels increased by increasing the contents of PAA, while gradually decreased with the increasing of Laponite contents. Thus, the contents of Laponite and AA can be adjusted for preparing hydrogels with different applications.