Study On Transmission And Heat Transport Performance Of Low-Dimensional Carbon Nanomaterials Under Defects

For materials,the macro-scale performance is often determined by the atomic and molecular structure at the micro-nano scale.Therefore,the molecular-scale simulation of the bottom-up study of materials,an important part of the multi-scale simulation of materials,helps explain new phenomena that cannot be analyzed by classical continuum mechanics,so as to trace the origin.At the microscopic scale,graphene and carbon nanotubes are hot low-dimensional materials in recent years.Their excellent mechanical and thermal properties make them have broad engineering application prospects.For example,doping applications in cement-based materials help improve cement hydration Product structure,improve durability,and solve the problem of thermal stress accumulation of large-volume concrete in hydraulic engineering.However,due to current technical means,low-dimensional carbon materials such as graphene in practical applications are mostly defective,and the randomness of their distribution leads to uneven material properties,resulting in limited applications.Therefore,the discussion on the influence of defects on the mechanical and thermal properties of low-dimensional carbon materials is of great significance to expand the engineering application range of materials,enhance the performance of composite materials,and realize the control of performance.In this paper,molecular dynamics methods are used to discuss the effects of dislocations and vacancies on the mechanical and thermal properties of carbon nanomaterials,which mainly include the following two aspects:(1)Edge effects and interlayer coupling effects have always been the key factors affecting the precise control of the rotation transmission system(RTS)based on carbon nanotubes(CNT).Considering the characteristics of combining the stable transmission of the armchair RTS and the same frequency output of the zigzag RTS,this work uses the 5|7dislocation defect to splice the armchair CNT and the zigzag CNT to form concentric heterogeneous carbon nanotubes,and uses the molecular dynamics(MD)method to systematically discuss the influence of 5|7 dislocation defects on the output frequency of the heterogeneous rotary transmission system.An extremely stable asynchronous output result was detected in a heterogeneous rotor wrapped by a saw-tooth stator,and it was found that the interlayer friction between the heterogeneous rotor and the stator would continuously change with the relative sliding speed or chirality distribution,which also determines whether the rotor keeps rotating with the motor synchronously.In addition,the heterogeneous RTS in a stable rotation state roughly includes two transmission edge layouts: head-to-head and plug-in,and respectively provide a constant input and output frequency difference and a constant output frequency.The research results further show that by changing the position of the defect,the friction between the heterogeneous rotor and the stator layer can be adjusted,and the coupling effect of the transmission edge can be affected,so as to realize the balance state of the rotor.(2)Defects,as an important factor leading to the decrease of the thermal conductivity of low-dimensional carbon materials,mainly affect the heat flow conduction process from the aspects of defect concentration and distribution.This study uses the non-equilibrium molecular dynamics(NEMD)method to discuss the influence of triangular vacancy defects on the thermal conductivity of graphene nanoribbons,and aims to further understand the mechanism of the defect effect and expand the scope of graphene thermal applications.In the heat conduction simulation of triangular defect graphene nanoribbons(TGNR),it is detected that there is a quasi-triangular area at the back of the defect where the heat flux is zero and the direction of the atomic heat flow vector is perpendicular or opposite to the heat flow transport direction,so it is defined as the scattering area.The removal of the scattering area under different conditions will have three different effects on the thermal conductivity: increasing,unchanging,and decreasing,which is different from the previous study on the negative correlation between defect concentration and thermal conductivity.In the discussion about the influence of the length of the bottom side of the defect on the scattering area at the back of the defect,the scattering areas of different sizes show a proportional triangle relationship.In addition,the front angle of the defect is proved to be an important factor affecting the relationship between the scattering area and the thermal conductivity by comparing the influence of triangle and square defects on heat flow transport.When the apex angle is greater than 60°,the front end of the defect will produce a scattering area similar to the back end,and the removal of the back end of the scattering area will have two opposite effects on the thermal conductivity: increasing and decreasing.But the special one is that the thermal conductivity of TGNR with a critical angle of 77.5° is not sensitive to whether to remove the scattering area.