Study On The Structure And Mechanical Properties Of Polycrystalline Graphene Oxide Based On Molecular Dynamics Simulation

Graphene has a special two-dimensional planar honeycomb structure and excellent performance,which is regarded as a new material with high strength of strategic significance.It has great application value in many fields,and is one of the research hotspots in biology,chemistry,physics,materials and other fields.As a derivative of graphene,graphene oxide has become a hot research object in nanomaterials and other fields due to its larger surface size,good water solubility and excellent mechanical properties.However,in the process of preparing graphene and GO with modern industrial technology,some structural defects(such as cracks,voids,etc.)will inevitably appear.These intrinsic defects or defects induced by external introduction affect the mechanical,electrical and thermal properties of graphene and its derivatives.Compared with perfect graphene with strict preparation process and low cost performance,graphene and its derivatives with grain boundaries and other defects also have certain application potential.Therefore,it is very important to utilize and control these defects on the basis of understanding and mastering their characteristics.In this paper,a new molecular configuration of GO containing grain boundary,namely polycrystalline graphene oxide,was constructed by using the perfect graphene and GO models.Stability and mechanical properties of the three were analyzed by molecular dynamics method.The"bottom-up"multi structure-spatial design performance of polycrystalline graphene oxide and the physical mechanism associated with spatial structure in mixed dimensions(Combination of sp~2and sp~3)were studied,The effect of defect coupling(grain boundary and functional group)on the mechanical properties was analyzed and discussed.The general research contents of this paper are summarized as follows:(1)According to the analysis of the research progress at home and abroad,the main results of the current research on graphene and graphene oxide at home and abroad are given.Some main research theories and methods about molecular dynamics simulation methods are summarized,and the research innovation points and specific research methods are put forward.(2)The basic mechanical properties of perfect graphene and GO were studied by molecular dynamics method,and the influence of temperature field,tensile strain field and oxygen content of functional group on their mechanical properties was simulated,which paved the way for the comparison with the new model(polycrystalline graphene oxide).Research shows that the mechanical properties decrease with the increase of temperature and increase with the decrease of tensile strain rate.When the tensile strain rate is higher than a certain value,the perfect graphene will undergo strain hardening phenomenon,which causes the tensile strength and corresponding strain phase of the material to increase at low strain rate.The mechanical properties of graphene oxide are not as sensitive to the temperature field as perfect graphene.It weakens slightly as the temperature increases,and at the same time becomes weaker as the oxygen content increases.During the tensile process,the GO carbon ring can form a closed carbon-oxygen ring with the oxygen atoms in the hydroxyl group,which transforms from the epoxy compound to the ether functional group,increasing the ultimate strain and toughness.(3)By comparing the mechanical properties of the model with the perfect graphene and GO,the rationality of the new molecular configuration-polycrystalline graphene oxide model was verified.The influence of fracture behavior and grain boundary on the mechanical properties of the model during the simulated tensile process was studied.At the same time,the causes of the mechanical properties change of the new model relative to graphene and GO were analyzed.Studies have shown that the grain boundary exhibits an"induction"effect on the fracture process of the carbon-carbon bonds of polycrystalline graphene oxide,and the six-membered carbon ring produces a"degradation"effect.Under the coupling action of the external field(tensile stress)and the internal field(grain boundary),the stress concentration phenomenon is more obvious than that of graphene and graphene oxide.The atoms at the grain boundaries are more likely to reach the critical threshold,and then clusters of defects are generated,which reduces the mechanical properties.(4)From the perspectives of energy change and atomic stress,the differences in the mechanical properties of polycrystalline graphene oxide with different functional groups are revealed,which provides a valuable reference for directional control of the mechanical properties.Polycrystalline graphene oxide connecting more hydroxyl groups can withstand greater tensile stress,but in terms of ultimate strain,connecting more epoxy groups will be higher.From an energy point of view,Polycrystalline graphene oxide containing only epoxy groups has the highest total energy before stretching and is the most unstable.At the same time,the energy required by stretching to the ultimate strain is also the minimum,so it is most likely to reach the fracture energy and lead to the destruction of the structure.From the perspective of atomic stress,the stress of the model is higher when the functional groups are distributed at the grain boundary than at the amorphous boundary.In the former case,the coupling effect of grain boundary and functional group defects is the largest,which results in the lowest mechanical properties of polycrystalline graphene oxide.