Several researchers have observed the intercalation of gases, metals and fullerenes into carbon nanotubes. In this study we examine the compressibility of carbon nanotubes that have been filled with noble gases, methane and buckyballs and compare the values to the compressibility of empty nanotubes. The approach is classical molecular dynamics simulations. The interatomic potential used in this study is the analytic reactive empirical bond-order potential of Abel-Tersoff that has been parameterized by Brenner (REBO), and coupled to a long range Lennard-Jones potential. To treat intermolecular interactions with higher precision we also used adaptive intermolecular potential (AIREBO). In this study, (10,10) carbon nanotubes that are 10.0 nm and 20.0 nm long are filled with methane, neon and buckyballs. Compression of the filled nanotube is performed by moving one end of the nanotube towards the other end with a constant velocity 41 m/s, while the other end is kept fixed. On every nanotube edge a layer that is several angstroms wide is subjected to Langevin frictional forces to maintain the nanotubes at a constant temperature and mimic the heat dissipation properties of a real nanotube bundle. No other constrains are applied to the system. We have examined how the stiffness of the nanotubes during compression depends on different factors such as: the type of filling particles, the density of filling, the length of nanotube, and the temperature. The simulations predict higher nanotube stiffness when the nanotube is filled with gases relative to the empty state. Some simulations predict lower nanotube stiffness when the nanotube is filled with buckyballs relative to the empty state, while others predict higher nanotube stiffness. One explanation for this prediction is that buckling requires a perturbation of some sort so that the nanotube knows in which direction to buckle and the presence of buckyballs which bounce off the inside walls increases the amount of perturbations in the direction transverse to the long axis. Higher gas densities increase the buckling force of the nanotube. We found that the longer nanotubes buckle at a lower compressive force than the shorter nanotubes. Furthermore, compression at higher temperature enables easier buckling.
Materials Science and Engineering, The University of Florida
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email: firstname.lastname@example.org http://mse.ufl.edu/faculty/ssinn/