Design, Three-Dimensional Assembly And Property Of Stimuli-Responsive Graphene-Based Hybrids

Stimuli-responsive materials have attracted a great deal of attentions over the past several decades. They can convert environmental stimulus, such as temperature, light, pH and stress into the signal to trigger the change in physical or chemical properties of materials. Owing to its excellent mechanical, electro active as well as thermoelectric properties, graphene-based nanohybrid and macroscopic-ordered materials hold huge potential promise in stimuli-response applications. Such intelligent graphene are good candidates for building novel biological industrial&engineering materials. In this paper, a series of stimuli-responsive graphene-based nanohybrids and macroscopic materials were designed and prepared. They show good performance in a wide range of applications such as microfluidic switch, photocatalyst and artificial tissue.Graphene/Fe3O4hybrids were prepared using a one-step solvothermal method in ethylene glycol using graphite oxide as the graphene precursor and FeCl3·6H2O as the Fe3O4precursor. The Fe3o4nanoparticles, with a diameter of100-200nm, were densely and randomly deposited on the graphene surfaces and intercalated between the layered graphene sheets. The electrical conductivity of the hybrid reaches1.011×102S·m-1and the saturation magnetization reaches83.6emu-g-1. The as-prepared magnetically-functionalized graphene hybrid was used for the functionalization of hydrogels for the first time.Aqueous-dispersed graphene/Fe3O4hybrids were prepared using a two-step method. The process of which includes the reduction of GO and the following in-situ decorating of reduced GO sheets with monodisperse Fe3O4. It is worth mentioning that reduced GO sheets are coated with poly(sodium4-styrenesulfonate) and Fe3O4nanoparticles are modified with oleic acid during this process, as a result of which the dispersibility of graphene/Fe3O4hybrids in aqueous is proved to be improved substantially compared to that of our previous products. The saturation magnetization of the as-prepared graphene/Fe3O4hybrid is obtained as22emu-g. Based on these results, functional microgels composed of the poly(N-isopropylacrylamide)(PNIPAAm) and the as-prepared graphene/Fe3O4hybrids were synthesized in a microfluidic reactor for the first time. The microgel exhibits a good response to the external magnet and the near-infrared (NIR) laser irradiation, indicating that it could be used as a light-driven and magnetic controlled switch for applications in microreactors.Next, we developed a universal approache for preparation of aqueous-dispersible stimuli-responsive graphene-based nanohybrid. Typically, we prepared a Cu2O nanocrystal-reduced graphene oxide hybrid that is dispersible in water, which is attributed to poly(sodium4-styrenesulfonate) coating. The Cu2O nanoparticles, with a diameter of3-5nm, were densely and randomly deposited on the graphene surfaces. The as-prepared hybrid responses to NIR light and visible light, demonstrates photothermal and photocatalytic effects, respectively, thus showing dual stimuli-responsibility.We produced a novel reduced graphene oxide foam (RGOF) through an ice-template filtering method. The product is free-standing, flexible, and elastic. Owing to its outstanding electrical properties, the RGOF demonstrates attractive temperature sensitivity based on thermoelectric effects in graphene. Furthermore, RGOF can also show pressure sensing behaviors under finger-pressures based on finger-heating effects. We have also produced a proof-of-concept RGOF pressure sensor-pad that can locate finger-pressure points and measure pressure levels. More importantly, all of these sensing abilities were demonstrated without any internal/external power supply. These results suggest that the RGOF holds promise for electronic skin applications.In this specific field, the development of a thin film material that is flexible and stretchable, sensitive enough to perceive touch, and yet able to heal itself following damage is profoundly interesting. We show that graphene and polymer nanoblocks can be integrated into a thin film which mimicked both the mechanical self-healing and pressure sensitivity behavior of natural skin without any external power supply. The most important component of our material design is the microstructuring of the strong and stretchable electrically self-healing electrode films. In this work, we used a poly(N,N-dimethylacrylamide)-poly(vinyl alcohol)/reduced graphene oxide (PDMAA-PVA/rGO) hybrid as the electrode film. We prepared self-healing pressure-sensitive hybrid films with electrospun piezoelectric poly(vinylidene fluoride) (PVDF) nanofibers sandwiched between PDMAA-PVA/rGOs. Combined with their outstanding mechanical properties and self-healing abilities, their pressure sensitivity makes these thin film materials promising candidates for artificial skin applications. Its tensile strain and maximum tensile stress are even two and ten orders of magnitude larger than the corresponding values of human skin, respectively. It also demonstrated highly stable sensitivity to a very light touch (0.02kPa), even in bending or stretching states.The above result strongly suggests that the functionalization of graphene could bring the attractive material novel stimuli-response abilities which don’t exhibit in pure graphene. In addition to the graphene-based hybrid thin film materials, we also investigated inorganic and organic modified graphene hydrogels, respectively.We report a room-temperature synthesis of chemically bonded TiO2(P25)-graphene hybrid hydrogels and their use as high performance ultraviolet light photocatalysts. The three-dimensional (3D) TiO2-carbon hybrid exhibits a significant enhancement in the reaction rate in the decontamination of methylene blue, compared to the bare P25. The3D P25-graphene hydrogel is much easier to prepare and apply as a macroscopic device, compared to the2D P25-graphene sheets. This work could provide new insights into the room-temperature synthesis of graphene-based materials. As a kind of the novel3D graphene-based hybrid, the obtained high performance P25-graphene gel could be widely used in the environmental protection issues.A self-assembled graphene-based hydrogel has been prepared with incorporated PNIPAAm chains through a hydrothermal method. The obtained hydrogel exibites reversible stimulus-responsive volume changes, which has never been realized for other graphene-based materials. The graphene-based hybrid hydrogels exhibit good electrical conductivity, high mechanical strength, reversible volume changes and a tunable electrical conductivity throughout the swelling/deswelling cycles. Furthermore, they undergo electro-responsive volume changes, which make them potential candidates for artificial muscle devices.For the biomimetic applications, an artificial material is also needed to be self-healing, electroactive and bio-applicable. Therefore, we further developed a strategy to build a graphene-PDMAA cross-linking structure based on graphene networks. The obtained hydrogel exhibits good neural compatibility, high conductivity, low impedance and efficiently near-infrared-triggered photothermal self-healing behaviours owing to its unique3-dimensional graphene-PDMAA cross-linking networks. The results indicate that the graphene-PDMAA hydrogel is one more step closer to simulating human tissues.