Orientational preference and influence of rotation on methane mobility in one-dimensional channels

Abstract

Molecular dynamics investigations of methane in one-dimensional channel systems of AlPO₄−5 and the carbon nanotube are reported. Methane shows contrasting orientational preference over 1+3 and 2+2 orientations inside AlPO₄−5 and the carbon nanotube. In AlPO₄−5, 2+2 orientation is preferred in narrow parts of the channel while 1+3 orientation is predominant in the wider part of the channel. In the carbon nanotube 2+2 is preferred over 1+3 orientation throughout the channel. Thus, the orientation of methane can yield insight into methane-host interactions. Simulations with and without allowing for rotation of methane suggest that rotation aids translational mobility of methane in both the channel systems studied. It is shown that molecules with certain orientations are associated with lower mobility, both in AlPO₄−5 and carbon nanotube. Further, translational motion exhibits diffusive behavior for methane in AlPO₄−5 and superdiffusive behavior in the carbon nanotube. These results suggest that particular orientation or rotation in general can strongly influence translational mobility of methane in one-dimensional channels. It is seen that levitation effects influence rotational motion in addition to the translational motion.