Study On Mechanical Properties Of Multilayer Graphene Oxide Based On Molecular Dynamics Simulation

As the macroscopic application of multilayer graphene oxide becomes more extensive,it is of great significance to understand the mechanical properties of macroscopic multilayer graphene oxide.In this paper,multilayer graphene oxide is regarded as a special transversely anisotropic material.The molecular dynamics simulation method was used to study the in-plane tensile properties of single-layer and multi-layer graphene oxide,and the effects of layer number,oxidation degree and temperature on in-plane tensile properties were studied.Then the multi-layer graphene oxide was prepared experimentally,and in-plane stretching was performed.The experimental results of the in-plane tensile properties of the multi-layer graphene oxide obtained at different temperatures were compared with the molecular dynamics simulation results to verify the calculation model.Since the out-of-plane tensile and shear properties of multilayer graphene oxide are significantly different from in-plane,molecular dynamics simulations were further used to study the three-dimensional elastic constants of the multilayer graphene oxide model,and to determine its threedimensional elastic matrix(compliance matrix and stiffness matrix),the influence of oxidation degree on three-dimensional elastic constant and strength was analyzed.The main research contents are as follows:(1)Firstly,single-layer graphene,graphene oxide and triple-layer graphene oxide models are established,and select appropriate boundary conditions for tensile and shear simulation,and in-plane tensile and shear simulations are performed to determine the simulation method that can realize Poisson effect and stable shear deformation.After that,two models of regular stacking structure and fully overlapping stacking structure of single-layer nanosheets were established to study their in-plane tensile failure modes.The results show that there are two failure modes in in-plane stretching,one is the rupture of carbon-carbon bonds under tensile load,and the other is the interlayer crosslinking(hydrogen bonding and van der Waals effect)weakened.(2)Analysis of influencing factors on in-plane tensile properties of multilayer graphene oxide.The results show that the tensile behavior of fully overlapped multilayer graphene oxide is different from that of monolayer graphene oxide.Under the same stacking number,the increase of oxidation degree has little effect on the Young ’s modulus of monolayer graphene oxide,and the ultimate strength and fracture strain decrease gradually.The fracture strain of multilayer graphene oxide is less affected,and the Young’s modulus and ultimate strength decrease gradually.At the same oxidation degree,the Young’s modulus and ultimate strength of multilayer graphene oxide are smaller than those of monolayer graphene oxide,and there is little difference in fracture strain.The calculation results at different temperatures show that with the increase of temperature,the Young’s modulus and ultimate strength at 1000 ℃are the largest,the Young’s modulus at room temperature is the smallest,the ultimate strength is in the middle,the Young’s modulus at 500 ℃ is in the middle,the ultimate strength is the smallest,and the brittleness increases.(3)Experimental study on in-plane tensile properties of multilayer graphene oxide.The uniaxial tensile test and characterization of graphene oxide films treated at different temperatures were carried out.The results show that the Young’s modulus and ultimate strength of graphene oxide films treated at 1000 ℃ are the largest,the ultimate strength at room temperature is in the middle,the Young’s modulus is the smallest,the ultimate strength at 500 ℃ is the smallest,the Young’s modulus is in the middle,and the brittleness increases.The influence of temperature on in-plane tensile properties of graphene oxide is in good agreement with the calculation results.(4)Molecular dynamics simulation calculates the elastic constant of the multilayer graphene oxide model and obtains its three-dimensional elastic matrix.The Young’s modulus and Poisson’s ratio of in-plane stretching of multilayer graphene oxide with different oxidation degrees,Young’s modulus and Poisson’s ratio of out-of-plane stretching,and modulus of shear were studied respectively.The calculation results show that with the increase of oxidation degree,the out-of-plane tensile properties and shear properties are improved,the in-plane tensile properties are decreased,and the Poisson’s ratio decreases.