Coalescence Mechanisms Of The Fullerenes In The Carbon Peapods With Kinked And Curved Structures

Carbon peapod, as a novel super-molecule, is a hybrid structure composed of the chain of fullerenes encapsulated in the 1-D hollow space of the host carbon nanotube. Further heating or electron irradiation can lead to the gradual coalescence of the encapsulated fullerenes with an inner tube formed ultimately. Despite the extensive studies to the structures, the coalescence mechanisms and the associated properties of the carbon peapods in both experiments and theories, most of the works only focus on the conventional carbon peapods with the straight carbon nanotube of no defects as the host tube but with rare attention to the coalescence behavior and the ultimate structure of the kinked and curved carbon peapods, which are very popular in the real experiments.Based on the empirical potentials and the energy driven kinetic Monte Carlo(EDKMC) method, the systematic simulation at the atomistic scale has been performed for the first time to study the thermal activated coalescence of the fullerenes in the kinked and curved carbon peapods targeting to explore the feasibility of the polymerization of the fullerenes and compare their behaviors between the conventional carbon peapods and the straight ones with no defect s and curvature in the host tube. The main contents are summarized as follows:(1) The angle of the kinked host tube and the relative position of the pentagon/heptagon defects at the junction have obvious influence to the coalescence behavior and the ultimate structure of the as-formed inner tube. Generally, the fullerenes filled in the kinked host tube are able to start to polymerize and form an inner tube wall resembling the kinked structure of the host tube with only one pentagon/heptagon defect produced at the kinked junction connecting two tubes with different chiralitys. The pentagon/heptagon at the kinked junction of the formed inner tube can copy the relative position of the host tube with smaller or larger kinked angle like(18,0)?(17,1) or(18,0)?(10,10), respectively. For the host tube with intermediate kinked angle like(18,0)?(15,5), the pentagon/heptagon will not copy the relative position like the host tube exactly due to the higher formation energy of the junction but rearrange their positions to reach the optimized configuration balanced by many energetic factors. Particularly, for the host tube with smaller kinked angle like(18,0)?(17,1), the coalesced fullerenes are able to form inner tube with no kinked junction, just like the fullerenes in the straight tube with no defect s. Meanwhile, determined by the kinetic mechanism with limited time scale during the simulation, the probability for the formation of the amorphous inner tubes with many topological defects also rises obviously.(2) For the curved carbon peapod with smaller curvature, the inner tube formed through the thermal activated coalescence of the fullerenes is able to copy the smooth curvature of the host tube with no defects created. With the increase of the curvature, however, the difficulties for the successful coalescence of the fullerenes are becoming larger and larger with the occurring of the structural transition for the inner tube from the smooth curvature to the kinked junction, which is determined by the energetic competence between the increased curvature energy and the formation energy of the kinked junction of the as-formed inner tube under the constraint from the host tube.(3) The statistics to the inner tubes with identified chiralitys simulated by many random trajectories prove that no matter the kinked host tube or curved host tube is able to alter the large chirality distribution discovered in the straight host tube and tune the wall-wall distances between the outer and inner tubes. Such a result means that we may tune the structures(e.g., chirality, diameters, kinks, curvatures, etc.) of the inner tubes by selecting the host tubes with different kinks or curvatures.