Predictions of a spiral diffusion path for nonspherical organic molecules in carbon nanotubes

The diffusive behavior of ethane and ethylene in single-walled carbon nanotubes is investigated using classical molecular dynamics simulations and density functional theory calculations. At low molecular densities, these nonspherical molecules follow a spiral path inside nanotubes with diameters of 13-22 A, which maximizes the interaction of molecular C-C bonds with the C-C bonds in the nanotubes. Spherical molecules, such as methane, are not predicted to follow a spiral diffusion path. This result quantifies the manner in which molecular shape and chemical bonding affects molecule-nanotube interactions and indicates the generality of spherical transport through nanotubes.