Temperature-sensitive poly(N-isopropylacrylamide)/graphene oxide nanocomposite hydrogels by in situ polymerization with improved swelling capability and mechanical behavior

To improve the performance of temperature-sensitive poly(N-isopropylacrylamide) (PNIPAM) hydrogels, graphene oxide (GO) was selected as a nano strengthening agent to prepare nanocomposite hydrogels. For fulfilling this purpose, in situ polymerization was carried out in colloid solution of graphene oxide, where N-isopropylacrylamide as temperature-sensitive monomer and N,N′-methylene bisacrylamide as crosslinker was initiated utilizing potassium persulfate and sodium sulfite as redox initiators. Infrared spectroscopy and transmission electron microscope was employed to characterize the structure of GO and its dispersibility in water respectively. The internal network structure of nanocomposite hydrogels was investigated by scanning electron microscope (SEM). The temperature-sensitivity, swelling and deswelling properties and mechanical performance of the as-prepared nanocomposite hydrogels was investigated preliminarily. Experimental results show that the nanocomposite hydrogels prepared not only possess good temperature-sensitivity but improved swelling capabilities. The volume-phase transition temperatures of most composite hydrogels are shifted to higher temperature than PNIPAM hydrogels. Furthermore, addition of appropriate amount of GO can dramatically enhance the mechanical performance of PNIPAM hydrogels. The compressive strength of nanocomposite hydrogels reaches a maximum of 216 kPa when the weight ratio of GO to NIPAM is ∼5%, which is 4 times larger than that of PNIPAM hydrogels (54 kPa). The advantageous performance of nanocomposite hydrogels over PNIPAM hydrogels is very beneficial for future applications.