Nanocomposite Gels Consisting of a Unique Polymer/Clay Network and their Characteristics
Intelligent polymer hydrogels such as poly(N-isopropylacrylamide) (PNIPA) hydrogel, consisting of chemically cross-linked networks, have long been of interest but are mechanically fragile materials limited to specific uses. Important innovations have been made as a result of the creation of a novel class of nanocomposite (NC) hydrogels with a unique organic/inorganic network structure. The NC gels were synthesized by the in situ free-radical polymerization of N-alkylacrylamides in the presence of an inorganic clay mineral (hectorite). An organic (polymer)/inorganic (clay) network structure, consisting of exfoliated clay platelets uniformly dispersed in an aqueous medium with a number of flexible polymer chains linking them together, was formed uniformly throughout the sample. The NC gels exhibited high transparency, high degrees of swelling, and superb mechanical properties with extraordinarily large deformations of > 1000%. In addition, the NC gels formed from thermosensitive polymers, e.g. PNIPA, exhibited rapid transparency and gel volume (de-swelling) temperature responses at the transition temperature. These optical, mechanical, and swelling/ de-swelling properties could be controlled over a wide range by altering the gel composition and modifying the network structure. The NC gels could thus simultaneously overcome most of the traditional limitations of conventional polymer hydrogels. Furthermore, the NC gels exhibited a number of interesting new characteristics. These results indicate that NC gels hold promise as soft functional materials that can be utilized in various applications.