Preparation and characterization of pH- and temperature-responsive hydrogels with surface-functionalized graphene oxide as the crosslinker

A methodology is described for the preparation of pH- and temperature-responsive semi-interpenetrating hydrogels with surface-functionalized graphene oxide (GO) as the crosslinker, N-isopropylacrylamide (NIPAM) as the monomer and sodium alginate (SA) as an additive. GO sheets were first prepared via an oxidation reaction in aqueous solution and then modified with 3-(trimethoxysilyl)propylmethacrylate (TMSPMA) via a silanization reaction. Free-radical polymerization of NIPAM and SA was then carried out with the presence of TMSPMA-modified GO sheets at 20 °C in a water bath, leading to the formation of pH- and temperature-responsive PNIPAM/SA/GO hydrogels crosslinked with TMSPMA-modified GO sheets. The effects of TMSPMA-modified GO sheets content on various physical properties were investigated. Results show that PNIPAM/SA/GO hydrogels undergo a large volumetric change in response to temperature. It also exhibits significantly larger water uptake compared to conventional PNIPAM/SA hydrogels. Moreover, the PNIPAM/SA/GO hydrogels have a much better mechanical properties than the conventional PNIPAM/SA hydrogels.