Abstract：Macroscopic graphene oxide film is composed of multilayer graphene oxide.The mechanical properties of multilayer graphene oxide can be described from three aspects : in-plane tensile, normal tensile and interlayer shear properties. The in-plane tensile properties are related to the strength of carbon-carbon bonds, and the transformation of sp2 to sp3 hybrid forms is the main reason for affecting the binding energy of carbon atoms. Normal tensile and interlaminar shear properties are related to interlayer interaction, and the strength of hydrogen bond and van der Waals interaction are two factors affecting interlayer interaction. Here we treat multilayer graphene oxide as a special three-dimensional orthotropic materials--transversely isotropic material, formulate a three-dimensional model of multilayer graphene oxide with hydroxyl and epoxy groups randomly distributed on the surface of graphene, and the in-plane tensile, normal tensile and interlaminar shear behaviors of multilayer graphene oxide are studied by molecular dynamics method. All five independent elastic constants E2, E3, μ12, μ32 and G23 of multilayer graphene oxide are obtained. Then, the three-dimensional elastic matrix (flexibility matrix and stiffness matrix) is determined, and the influence of oxidation degree on the elastic constants and strength is further analyzed. It is found that normal tensile and interlaminar shear properties are much lower than in-plane tensile properties. With the increase of oxidation degree R, the in-plane Young's modulus E2 and tensile strength σ2max of multilayer graphene oxide decrease gradually, and the normal Young's modulus E3 and tensile strength σ3max, interlayer shear modulus G23 and shear strength τ23max increase gradually, but the influence on Poisson's ratio is small. The in-plane tensile fracture position is determined by the bond energy between the oxidation groups (hydroxyl and carboxyl) and carbon atoms. The number of hydrogen bonds is an important factor affecting the interlayer properties.
2022, Vol. 43 
