Nanoparticles Induced Graphene Scrolling And Configuration Transition

Graphene is a mono-atomic layer of carbon atoms arranged in a dense honeycomb lattice with sp2-bonding. Becaquse of the unique two-dimensional nanostructure and extraordinary properties, graphene and graphene-based materials have shown promising potential applications in material science, physics, chemistry, biology, medicine and many other fields since it was found in2004, and attracted tremendous attention from both the theoretical and experimental scientific communities. The successful preparation of planar two-dimensional graphene seems to contradict the common viewpoint that the two-dimensional crystals with mono-atomic layer hardly exist. Although recent experimental and theoretical studies suggested that nanometer-scale corrugations through the free graphene membrane are responsible for the stable existence of graphene in the finite temperature, it is still not clear to how these ripples stably hold the two-dimensional crystal, or in other word, what factor can induce the structural transition of graphene. It needs to be further improved, and several basically physical and chemical issues involved also need to be resolved urgently. Moreover, the studies on unique properties and practical applications of graphene mainly depend on its flat two-dimensional structure. The scrolling and deformation of graphene induced by size or external condition will cause the graphene to lose its ideal optical, mechanical and conductivity characteristic. Therefore, the studying the instability and the condition of phase transition, process and mechanism of graphene is a very important subject, which is crucial to explore the practice application of graphene.In this dissertation, we lay emphasis on graphene and nanoparticles, trying to deeply study and discuss the interaction between the graphene and nanoparticle by the molecular dynamics (MD) simulation, disclose the instability of graphene induced by nanoparticle, analyze the self-scrolling wrapping behavior and structural transition mechanism, explore the interaction mechanism. The primary coverage and results of the dissertation are as follows:(1) MD simulations were carried out to study the self-assembly of graphene and metallic nickel (Ni) nanowire. It is studied the effect of the graphene chirality, the size and shape of metallic nanowire on the stability and structure of graphene. It is found that the Ni nanowire can help the graphene overcome the energy barrier and provide driving force to drive the graphene self-scroll rapidly on the surface of the nanowire. The potential energy of system suggests that the self-scrolling of graphene is an energy decreasing process. The self-scrolling of the graphene is achieved by the wrapping of graphene onto the metallic nanowire successfully and forms a composite nanostructure composed of graphene and metallic nanowire. The self-scrolling of the graphene provides a simple route to produce the metal/carbon core-shelled nanostructure in theory. Compared with the traditional preparation method, this self-assemble method can be performed at room temperature, and the size and structure of the two parts can be accurately controlled. It is more convenient and simple than the encapsulation of the metallic particle into carbon nanotubes and it is of great significance for the practical applications of graphene.(2) On the basis of the first part, we further studied the interaction of the graphene and the metallic iron (Fe) nanowire, discussing the effect of the size of graphene layer, the relative orientations of the Fe nanowire and the graphene on the stability and structure of the graphene. The results indicate that the planar two-dimensional structure is not stable but metastable. Once the metastable state is broken, the phase transition of flat graphene would take place. The decline of the potential energy of the whole system suggests that the self-scrolling of the graphene onto Fe nanowire is spontaneous, and the system is increasingly stable during this process. The self-scrolling of graphene and the final core-shelled nanostructure can be controlled by the relative orientations of the graphene and the Fe nanowire, initial angle and graphene width. The MD simulation combined with ab initio spin-unrestricted density function theory (DFT) and thermodynamics is used to explain the interaction mechanism between the graphene and the metallic nanowire. We propose a thermodynamics model, to predict the structural transition process of graphene activated by the Fe nanowire and explain the instability and self-scrolling behavior of graphene.(3) Systematically studied the interaction of graphene nanoribbon (GNR) and the single-walled carbon nanotube (SWNT). In this part, we discuss the effect of the width of the GNR and the chirality and size of SWNT on the configuration of GNR, and explain the interaction mechanism. The results are helpful for deep understanding of the structural instability of two-dimensional materials. MD simulation is carried out to study the helical wrapping of GNR onto the external wall of SWNT and helical insertion of GNR into the cavity of SWNT. GNR adheres on the tube wall to form strong composite structure. When the interior of the SWNT is fully filled, the GNR head will be captured by the inner hollow space of the former formed GNR helix and produces a double-shelled helix at the one entrance of the tube. Two GNRs would form a DNA-like double-helix on the external surface and cavity of SWNT. These helical structures formed by GNR are quite close to the helices found in nature. The form of the GNR helix are resulted from the combined action of the van der Waals interaction, the offset face-to-face π-π stacking interaction between the GNR and the SWNT and the dangling a-orbitals on carbon atoms at open edges of GNR. The helical wrapping and encapsulation of GNR to the SWNT is the objective requirements that the helix takes the least amount of energy and natural space saver. The velocity of GNR in helical wrapping is obviously lower than that in helical insertion. The diameter and chirality of tube have a neglected influence on the wrapping, while the encapsulation is limited by the diameter very greatly. The GNR-SWNT system has also been validated that it is of great importance in substance delivery at the nanoscale level. It demonstrates that the GNR-SWNT system can be used as nanoscale conveyor-belt to finish the effective delivery of medicine and other substance in the nanoscale space.The research results are not only crucial to deeply understand the thermal stability and structural transition, explore superb properties of graphene at an atomic level, but provide important theoretical significance to explore and utilize the composite materials of graphene and nanoparticle, and to expand the practical application of graphene to many other realms.