Remote control of volume phase transition of hydrogels containing graphene oxide by visible light irradiation

Poly(N-isopropylacrylamide-co-sodium acrylate) and graphene oxide (GO) composites were prepared by a simple mixing of a solution containing the monomers and aqueous GO through chemically initiated polymerization. We found that exfoliated GO sheets were well-dispersed in the hydrogel matrix and absorbed visible light and consequently generated heat. By combining the photothermal GO with the thermally responsive hydrogel matrix, we demonstrated a volume change of the hydrogel triggered by visible light irradiation of modest intensity. The volume phase transition of the composite hydrogel was fully reversible and could be repeated multiple times without any significant variation. Furthermore, the degree of volume change could be controlled by the light intensity and exposure time as well as the concentration of GO in the hydrogel.