Study On Adhesion And Self-assembly Of Carbon Nanostructures Dominated By Interlayer Interactions

The development of nanotechnology has broadened the horizon of human understanding of the world,nanotechnology is widely used in materials,microelectronics,energy and biomedical fields,and greatly improves the quality of life of people.Unlike macro-materials,nano-scale materials exhibit peculiar physical,chemical,optical,electrical and mechanical properties.Graphene and carbon nanotubes(CNTs)are typical carbon nanomaterials,because of their excellent mechanical,electrical and optical properties,graphene and CNTs have broad prospects in many fields and have received wide attention.However,due to the small out-of-plane bending stiffness and large surface area of graphene and CNTs,interlayer interactions may have a significant influence on the structural configuration and lead to change in mechanical,electrical and optical properties,which may bring challenges and opportunities for their applications.In this paper,graphene and CNTs are used to study the deformations and self-assembly behaviors of carbon nanostructures under interlayer interactions,in which the theoretical model and molecular dynamics(MD)method are used.The research works of this thesis are stated as follows:(1)A theoretical model to study the deformation of graphene under interlayer adhesion is established,and the configurations and stabilities of the scrolled and folded multilayer graphene are studied.The finite deformation beam equilibrium equations and the corresponding boundary conditions are used to solve the scrolled and folded configurations,and the analytical relationships between the deformation configurations and the geometric parameters are obtained;the bending energy and adhesion energy are calculated,and the optimal configuration and energy are solved by the principle of minimum energy.In order to verify the correctness of the theoretical model,MD simulations are used to calculate the atomic structures and energies of the scrolled and folded graphene.The scrolled and folded configurations calculated by the theoretical model are consistent with the MD simulations results.The energy map shows that,the energy of the scrolled or folded graphene decreases with the increase of length,and there exists metastable and stable states with respect to the plane state.Meanwhile,with the increase of the length,due to the scrolled graphene has a longer adhesion region,its energy is lower than the folded configuration and the scrolled configuration is more stable.(2)The adhesion behaviors and stabilities of parallel multi-walled CNTs are analyzed based on the theoretical model.The configurations and corresponding bending energies of the partially and fully collapsed CNTs are derived by the finite deformation beam theory,the adhesion energies include contact and non-contact adhesion energies are considered,and the optimal configurations and corresponding energies are solved by minimizing the total energy.In order to verify the correctness of the theoretical model,MD simulations are used to study the adhesion behaviors between CNTs.The partially and fully collapsed configurations obtained by theoretical model are consistent with the MD simulation results.The results shows that,the energy of partially or fully collapsed CNTs decreases with the increase of diameter,and there exists corresponding critical diameters.The relationships between the critical diameters with bending stiffness,adhesion strength,interlayer distance and the number of layers are analyzed by analytical and fitting methods.(3)The collapsing process of CNT under external loading is analyzed by the theoretical model.The sectional configurations and bending energies of the freestanding CNT and the CNT adhered to the substrate under the displacement load are derived by the finite deformation beam theory.The adhesion energies and adhesion forces of CNTs during collapse are calculated by the analytical model.The optimal configurations,energies and loading forces are solved by the principle of minimum energy,and the energy barriers and radial deformabilities of CNTs during collapsing are analyzed.MD simulations are used to study the collapse process of CNTs,and the deformations and energies of CNTs are calculated to verify the correctness of the theoretical model.The deformed configurations,energy and loading curves calculated by the theoretical model for CNTs during collapse are consistent with the MD simulations results.It is found that,the energy barrier and radial deformability decrease with the increase of the CNT diameter,indicating that CNT with a large diameter is more prone to collapse.(4)The dynamic propagation of folding deformation for graphene under adhesion is investigated.The graphene nanoribbon can produce a continuous folding deformation under the interlayer interactions which is similar to the domino effect,and this phenomenon can be used to realize the self-assembly in nanostructures.The characteristics of critical condition and propagation velocity for domino folding of 2D materials are studied by MD simulations and finite element analysis,the expressions between folding critical condition and steady propagation velocity with bending stiffness,tensile stiffness,adhesion strength and other material properties are established by the approximate model,and are verified by MD simulations and finite element analysis results.Compared with the CNT domino collapsing,graphene domino folding is faster and more stable,since the boundary of graphene in width direction is free,while the CNT cross section is subjected to the symmetric boundary constraint and perimeter constraint during the collapsing process,which contributes large resistance.And when the diameter of the CNT increases,the flip-flop collapse would happen and further inhibits the propagation speed.In addition,a nano-driven device is constructed by utilizing the domino folding of graphene and can be used to accelerate nanoparticles,in which automatic excitation and drive can be achieved by nanotube hetero-junctions.This thesis studies the deformation and self-assembly behavior of carbon nanostructures under interlayer adhesions,which is helpful to understand the deformation characteristic and mechanism of structures in nanoscale,and can provide guidance for the fabrication and application of carbon nanostructures.Meanwhile,the theoretical model is suitable for other materials and can be extended to adhesion problems of other nanostructures.