Strength of up to 1.1GPa graphene film to achieve large-scale, continuous production!
As the two-dimensional material first to be discovered and studied, graphene has extremely excellent physical and mechanical properties, such as tensile strength inner surface theory, electrical conductivity and thermal conductivity, respectively, up to 130 GPa, 108 S m-1 and 5300 W m-1 K-1, it is considered the best and most potential structural and functional materials. In order to obtain graphene macro applications, the current mainstream strategy is small-sized graphene derivative (such as graphene oxide GO) to assemble the macro films, fibers, or bulk material by various methods. However, a large number of studies show that the mechanical strength of the macro graphene thin film material prepared by assembling much lower than the predicted value, and the main cause of this problem is the preparation of graphene process, the outer surface of the flexible graphene and solvent evaporation strong capillary forces caused by the large number of random cause wrinkles in the film. These random wrinkles cause stress concentration and the electron, phonon scattering problems resulting in reduced graphene film strength, electrical conductivity and thermal conductivity. To solve this problem, superb Zhejiang University, Xu Zhen joint team of Xi\’an Jiaotong University, Professor Liu Yilun creative team developed a solvent intercalation plastic stretching method for the continuous production of GO films for secondary plastics processing, greatly eliminate random internal film wrinkles while increasing the graphene crystallinity and macro, micro stacked orientation. After Herman degree of ordering of graphene films obtained after chemical reduction of 0.93, tensile strength and modulus are up to 1.1GPa and 60.27GPa, thermal conductivity and electrical conductivity reached 109.11 Wm-1K-1 and 1.09 × 105Sm -1, and the material strength of the composite structure of the obtained epoxy resin 634 MPa. At the same time, this approach also allows large-scale, continuous preparation, thus showing great potential in industrial practice. The study, entitled \”Continuous crystalline graphene papers with gigapascal strength by intercalation modulated plasticization\” of papers published in the latest issue of \”Nature Communications\”. 
[GO solvent intercalation plasticized film]
The RESEARCHWork study significantly improved strength mainly depends on the graphene film and increase its internal wrinkle eliminating random orientation and crystallinity. Polymer materials by heat or solvent action inspiration plasticized characteristics of the film that the graphene sheet precursor GO rearranged to eliminate internal random wrinkles graphene thin film and an effective method to improve the alignment. To achieve this, the macro OF GO film layer interposed plastic stretching secondary solvent treatment – during the continuous pulling and stretching the film through manipulation macro GO ethanol solution tank, as shown in FIG. Ethanol into the solution tank, the original hard macro GO film flexibility is increased while after the ethanol molecules into the sheet layer can be increased GO GO sheets layer spacing (increased from 0.90 to 1.58 nm). This solvent intercalation will make interaction is weakened between the GO sheets, under the action of the traction force GO sheet connects damage and remodeling occurs continuously, slip dislocations are formed while improving the plastic film, further possible to flatten the wrinkles. The results show that, GO film elongation at break after plasticizing solvent intercalation stretching treatment reached 10%, showed a typical characteristic of plastic deformation; without doing any post processing GO film elongation at break was only 3% , exhibited elastic deformation and brittle fracture characteristics. Meanwhile, the author also used in real time to characterize the change POM and SAXS GO pulled during film structure, the film was found pulled wrinkles with increasing strain decreases, and the stretched film may also cause the degree of orientation in the GO nanoscale increase.
[graphene film macroscopic and microscopic structural change]
GO film obtained after the final chemical reduction of graphene films, of the microstructures, nanostructures and atomic structure of the film was analyzed and characterized. On the microstructures, SEM results showed alignment with the solvent type wrinkle intercalation process traction plastic stretching ratio increases, the film surface wrinkles random graphene disappear first, and then stretched in the direction along appears structure. SAXS and WAXS results show that the graphene thin film nanoAtomic scale and orientation have taken place, when the drawing ratio in the drawing process was 8%, Herman raised from the original order of 0.85 to 0.93. Meanwhile, XRD results show solvent after intercalation plastic stretching, crystallization of the thickness of the graphene increased by 65%, indicating that the stretching treatment not only improves the macroscopic, microscopic degree of orientation of graphene films, graphene can be improved crystallinity, and TEM results of this conclusion is further proof.
[graphene thin film performance]
first of graphene films and mechanical properties of the composites were characterized showed the disappearance of the internal random graphene thin film and enhance the crystallinity and orientation degree of wrinkles increase dramatically the mechanical strength of the film. Plasticizing solvent intercalation stretching process than 8%, the modulus of the graphene film reached 60.27 GPa (close modulus aluminum alloy), 7.6 GPa as compared to untreated graphene films, improved 693%. After the graphene film after secondary treatment to improve the tensile strength 1.1GPa, than the strength of 524.32 N m g-1, higher specific strength aluminum alloys and titanium alloys. Subsequently, the graphene thin film of the epoxy resin after secondary treatment layered composite structure prepared composite material strength and modulus are up to 634 MPa and 25 GPa. Meanwhile, the authors found that the thermal conductivity and electrical conductivity of graphene film after subjected to solvent intercalation may be plasticized been greatly enhanced, respectively, can reach up to 109.11 W m-1 K-1 and 1.09 × 105 S m- 1. After the epoxy compound, in addition to having excellent mechanical strength, excellent electrical conductivity which is still well maintained (3.1 × 104 Sm-1.), At 2 ~ 18GHz frequency of electromagnetic waves, electromagnetic shielding factor of between 30 between ~ 40 dB, thus indicating the great potential in the future of aerospace equipment.
Summary: A New Method of the solvent intercalation of using plastic stretching, macro graphene sheets stacked aggregation structure and microstructure was reorganized and optimized so that the final mechanical strength of graphene films, electrical conductivity and thermal conductivity has been greatly improved. Meanwhile, this method may further large scale and continuous preparation of a large-sized graphene thin film materials, thus making it an excellent material properties graphene structure in the future engineering applications can be practical. Original link: https://www.nature.com/articles/s41467-020-16494-0
