A Comprehensive Study on the Encapsulation of Methane in Single-Walled Carbon Nanotubes

This paper aims at exploring the characteristics of a single methane molecule encapsulated in semi-infinite single-walled carbon nanotubes. On the basis of Lennard-Jones potential function along with the continuum approximation and applied mathematics, single integrals are presented to formulate the van der Waals interaction energy and suction energy between a single methane molecule and a carbon nanotube. The preferred position and orientation of methane with regard to the nanotube axis has been fully investigated for different nanotube radii. To this end, it is assumed that the whole molecule rotates in all directions inside the nanotube. It is found that for certain radii of nanotubes in which the suction energy imparted to methane is negative, the whole methane molecule is symmetric with respect to the tube axis when it is inside the carbon nanotube. But, when the suction energy has positive values, as the tube radius increases the methane molecule gets closer to the wall of nanotube and finally locates near its wall in the form of a downward tripod. Furthermore, the optimum nanotube radius which gives rise to maximum suction energy has been calculated. The results obtained in this study can be conducted as means of further investigations for methane storage in carbon nanotubes.