Molecular simulations on separation of atoms with carbon nanotubes in torsion

Partition of noble atoms is studied using a pre-twisted single-walled carbon nanotube with semi-capped end via molecular dynamic simulations. A small portion on one end of the carbon nanotube is initially twisted to form a torsion buckling state. Upon releasing the pre-twisted portion, the collapse propagates along the tube wall. The van der Waals force between the encapsulated atoms and the collapsed wall of the nanotube thus initiates a motion and a consequent separation of the atoms. A successful separation of different atoms is found to be owing to the difference in the inertia of the atoms and the barrier effect of the semi-capped tip of the nanotube. Motions of one neon atom and one xenon atom are simulated to illustrate the separation process and various effects, such as twist angle and semi-capped tip, on the effectiveness of the process are discussed. Separation of eight atoms, four neon and four xenon, is demonstrated to further show the practical potential of the proposed partition method.