Molecular Dynamics Study On Sliding Friction Behavior Of Several Graphite Nanomaterials

In recent years,new nanomaterials such as graphene and carbon nanotubes have been gradually discovered in practices and experiments which have been found to have not only the excellent thermal conductivity and also optical properties,but also excellent tribology performance.Based on this,materials such as carbon nanotubes and graphene have potential to be used in nanodevices in order to greatly improve the service life.In this manuscript,the molecular dynamics method is used to explore the interlayer sliding of nano-carbon materials.The main works are as follows:(1)In this paper,the sliding friction behavior of carbon nanotube/copper heterostructures is studied firstly.In the simulations,the sliding processes of carbon nanotubes on the three different low-index crystallographic planes was investigated.Further,we also measured the average sliding friction force as a function of CNT length and sliding velocity.In addition,the influence of surface groups of carbon nanotubes on friction is also discussed.It is pointed out that the different graft ratio can affect the frictional properties of nanotubes.The contribution of hydrogen atoms to the total friction during the sliding processes are also explained.(Chapter 3)(2)Secondary,this paper discussed the sliding process of two layer graphene under various conditions and the convert from commensurate to incommensurate states.The sliding models of homogeneous graphene were established.Through the simulations of the sliding processes,the changes of trajectories and the friction responses during the transition from stick-slip state to smooth-sliding state of graphene were explained.The relationship between the cause of stick-slip and the commensurability,that is,the relationship of twist angle,is described,and the relationship between the generation of superlubricity and the twist angle between layers is explored.Furthermore,the changes of full width at half maxima(FWHM)in different sizes are also described.Furthermore,by plotting the potential energy surface(PES)of the graphene layer to analyze the trend of potential energy on the sliding path,the root cause of the friction is explained.The one-dimensional spring oscillator model is used to analyze the sliding process of graphene.The relationship between the interlayer equivalent stiffness and the spring stiffness and the condition which stick-slip state occurs are described.(Chapter 4)(3)Finally,the interlayer sliding process of two-dimensional heterostructures is investigated.The graphene/molybdenum disulfide heterojunctions with twist angle = 0° is adopted in the simulations.In addition,the sliding behavior,friction force and coefficient of the system under various flake sizes and normal loads are analyzed.The influence of graphene size on superlubricity of heterostructures is described.At the same time,this chapter also describes the effect of Moiré superstructure formed between the two-dimensional heterostructure on the structural superlubricity.(Chapter 5)The conclusions above contribute to a deeper understanding of the sliding friction process on the surface of single crystal atoms,and provide a theoretical reference for the application of carbon nanomaterials in nanostructures and micro/nano devices.