Preparation And Properties Of Polyacrylami-De/Graphene Oxide Nanocomposite Hydrogels

Hydrogels with good water absorbability, water-retention and biocompatibility have been widely used in our daily life. However, conventional polymeric hydrogels cross-linked by organic cross-linkers are usually mechanically weak, limiting the application of hydrogels to some extent. In recent years, overcoming this limitation and enhancing the hydrogels has become a hot research area in the scientific community. In the present paper, an organic/inorganic nanocomposite hydrogel with excellent tensibility is prepared by using graphene oxide (GO) as cross-linker. The main work is as follows:(1) Polyacrylamide (PAM) nanocomposite hydrogels with tiny inorganic GO and organic N, N'-methylenebisacrylamide (BIS) as co-cross-linker were synthesized via in-situ free-radical polymerization of acrylamide in aqueous suspension of exfoliated GO. The tensile and swelling properties of as-synthesized hydrogels were investigated. Comparing with conventional chemically hydrogels cross-linked by organic BIS with AM, the PAM/(GO-BIS) hydrogels exhibit high strengths and large elongations at break (2500%).(2) On the basis of above studies, we prepared PAM/GO hydrogels by the same method as PAM/(GO-BIS) only with GO as the cross-linker. Comparing with conventional chemically cross-linked hydrogels, the PAM/GO hydrgels exhibit astonishingly large elongations at break, high tensile strengths, extraordinary mechanical toughness and restorability. The elongation at break of PAM/GO hydrgels is nearly one order higher and the tensile strength is about 4.5 folds higher than those of conventional hydrogels even with tiny of GO content in a hydrogel. Furthermore, the tensile strengths reach maximum value (385KPa) as the weight of GO is 6 g/lOL H2O, while there is no obvious change in the extremely large elongation at break (>3100%) with increasing GO content. The cross-linking structure of the hydrogels was analyzed by using ATR-FTIR, DSC and XRD. Combined with the theoretical calculation on the number of cross-linked polymer chains per unit volume of gels (N*), a structure model is thereafter proposed. Besides, the influence of external factors on the swelling property of PAM/GO hydrogels was investigated. We also analyzed the swelling dynamic behaviors of PAM/GO hydrogels. The results indicate that the swelling properties of PAM/GO hydrogels are better than that of conventional hydrogels. The swelling ratio of PAM/GO hydrogels is increased gradually with the rise of external temperature, and the swelling behavior of PAM/GO hydrogels is mainly affected by the relaxation control of polymer chain in the network structure. Swelling dynamics of PAM/GO hydrogels conforms to second-order rate equation.