Preparation And Properties Of Near Infrared Response Graphene-polymer Hydrogel

The main purpose of this paper is the preparation of near infrared driving graphene-polymer composite hydrogel. First, the synthesis of robust and thermo-response graphene oxide(GO)-poly(N-isopropylacrylamide)(PNIPAm) hybrid hydrogels, and the graphene-PNIPAm nanocomposite hydrogels with high tensile properties and electro conductibility. Second, the preparation of the infrared-driving actuator based on the thermo-response of PNIPAm and the IR absorption of GO. Third, the preparation of the fast self-healing graphene composite hydrogel induced by NIR laser based on the IR absorption of GO and the thermal plasticity of poly(N,N-dimethylacrylamide)(PDMAA) NC hydrogels. Fourth, The synthesis of graphene-based double-network(DN) composite hydrogels with high strength based on the high strength GO-polyacrylamide(PAAm) hydrogel and alginate-Ca2+ network. The main workss and results are as follows:1. GO based hydrogels were proposed to be used as biomaterials and stimuli-response materials, but their poor mechanical properties restricted their applications. We enhanced GOPNIPAm hydrogels by hybrid with the hectorite clay through in situ polymerization for the first time. This clay was found to stabilize the GO in the aqueous suspension when a reducer was added in a redox initiating pair. These GO-clay-PNIPAm hybrid hydrogels exhibited a high mechanical strength and extensibility with the GO sheets as the cross-linker and with the hectorite clay as both the cross-linker and reinforcing agent. They were thermal-responsive with the volume phase transition at 34 oC. Reduction of the GO with L-ascorbic acid under environmental friendly conditions resulted in a high conductivity to the graphene-clay-PNIPAm hydrogels. These graphene-clay-PNIPAm hydrogels still had desirable mechanical properties. This finding has provided an easy method to prepare strong and stimuli-response graphene-polymer hydrogels to meet the demand for the newly developed soft matter.2. Stimulus-responsive hydrogels are utilized driving materials in actuators for transforming external signal into actuation movements. Infrared(IR) irradiation is considered to be an ideal driving energy because it can penetrate into biomaterials without direct contact and can be remotely controlled. In the present work, a new IR-driving bilayer hydrogel actuator is prepared by stacking a GO-clay-PNIPAm gel layer onto a clay-PNIPAm gel layer, synthesized through stepwise in situ polymerization. GO in the gel absorbs the IR irradiation and rapidly and efficiently transforms it into thermal energy, resulting in a much faster temperature increase in the GO-containing gel layer than that of the gel layer without GO, and the temperature of the former becomes higher than that of the latter. This bilayer structure with different temperatures changes the isotropic volume contraction into an anisotropic deformation, i.e., bending, which is always toward the GO-containing layer. Moreover, this bending occurs in the atmosphere, owing to the self-supporting capability of the tough gels. The repetition of the bending recovery is realized by turning the IR light on and off. According to these observations, the bilayer gel with GO provides a tough and IR-driving material for new soft actuators.3. We prepared GO-clay-PDMAA hybrid hydrogels with enhanced mechanical properties and fast self-healing capability realized by near-infrared(NIR) irradiation. The physical cross-linking between clay sheets and PDMAA chains provided the hydrogel with mechanical strength to maintain its stability in shape and architecture. GO sheets in the hybrid hydrogels acted as not only a collaborative cross-linking agent but also as a NIR absorber to absorb the NIR irradiation energy and transform it to thermal energy rapidly and efficiently, resulting in a rapid temperature increase of the GO containing gels. The chain mutual diffusion and the reformation of physical cross-linking occurred more quickly at higher temperature; consequently, the damaged hydrogel was almost completely recovered in a few minutes upon irradiation. We also demonstrated a potential application of the hybrid hydrogel as a self-healing surgical dressing.4. We report the synthesis of GO-PAAm hydrogels exhibited a high mechanical strength and extensibility with the GO sheets as the physical cross-linker through in situ polymerization. At the same time, we also report that GO-PAAm-alginate DN hydrogels can simultaneously achieve high strength and extensibility, self-healing. We attribute the gels’ high strength and extensibility to the synergy of two mechanisms: crack bridging by the physical crosslinking network between PAAm chains and GO sheets, and hysteresis by unzipping the network of ionic crosslinks. Furthermore, the network of between PAAm chains and GO sheets preserves the memory of the initial state, so that much of the large deformation is removed on unloading. The unzipped ionic crosslinks cause internal damage, which heals by re-zipping.