The effect of graphene on the lower critical solution temperature of poly(N-isopropylacrylamide)

Abstract

N-isopropylacrylamide is grafted on graphene by free radical polymerization to produce a series of graphene–poly(N-isopropylacrylamide) (PNIPAM) hybrid materials with different contents of graphene. The lower critical solution temperatures of the resulting materials have been investigated by ultraviolet–visible transmission spectroscopy. The result shows that the lower critical solution temperature of the resulting materials increases with the content of graphene increasing, and can be tuned to the human body temperature (37°C) when the content of graphene is in the range of 10–30%, which is very important for application of the hybrid materials in biomedical field. The result is ascribed to the high surface area of graphene that could graft a large amount of PNIPAM molecules and the immobilization of one end of PNIPAM chain on the surface of graphene. To further understand the effect of graphene on the lower critical solution temperature of PNIPAM, atomic force microscopy has been used to trace the morphology change of the hybrid materials in solid state with the temperature increasing from 33 to 40°C.