Comparison of CH4 and O2 transport through opened carbon nanotubes:: Predictions from molecular dynamics simulations

Computational studies of the properties of molecules confined in nanoporous materials have been undertaken by many research groups to predict their behavior for such applications as molecular sieves and hydrogen storage. Carbon nanotubes; have especially high potential to be used for environmental and pharmaceutical applications because of their uniform, cylindrical channel structures and propensity to close-pack into ordered arrays. This paper summarizes the results of classical, nonequilibrium molecular dynamics simulations that are used to predict the dynamic transport behavior of methane and oxygen molecules through opened, single-walled carbon nanotubes. Empirical potentials are used to calculate the forces in the simulations. For nanotubes with diameters below about 20 angstrom, the gas molecules move via normal-mode, single-file, and superdiffusion modes depending on the properties of the nanotubes. Within individual nanotubes, molecular transport can transition from one diffusion mode to another and the mass transport system changes from nonequilibrium to near equilibrium behavior over the course of the simulations.