AVS 50th International Symposium
    Nanotubes Wednesday Sessions
       Session NT-WeP

Paper NT-WeP20
Molecular Dynamics Study on the Non-equilibrium Flow of Small Molecules through Opened Carbon Nanotubes

Wednesday, November 5, 2003, 11:00 am, Room Hall A-C

Session: Poster Session
Presenter: K. Lee, University of Florida
Authors: K. Lee, University of Florida
S.B. Sinnott, University of Florida
Correspondent: Click to Email
Ultrafiltration membranes made of short, opened carbon nanotubes, which have relatively uniform nanometer-scale pore sizes and linear structures, may allow gases to selectively pass through the membrane. This potential selectivity can be predicted from atomistic simulations of the diffusion and adsorption of the gases into and within carbon nanotubes. The computational nanofluidics of hydrocarbons, oxygen, and carbon dioxide has been studied with molecular dynamics simulations in the work reported here. The microscopic behaviors of these gases can be simulated with multiple integrations of the interactions among the atoms in a system. The transport of gas molecules for long time periods is characterized by initial non-equilibrium states followed by equilibrium states. The non-equilibrium state is induced by the diffusive motion of the gas molecules from one end of the nanotubes into the vacuum or low-pressure region at the other end of the nanotubes, and lasts until the gases are evenly distributed in the nanotubes. During the non-equilibrium state, the gas molecules move back and forth through the nanotubes. It is found that this behavior, the time needed for the attainment of equilibrium, and the molecular motions at the openings of the nanotubes are affected by the density (or pressure) of gas molecules both inside and outside of the carbon nanotubes. When the gas molecules reach the end of the nanotubes, the attractive force between the tube end and the gas molecules prevent the molecules from leaving the nanotube. In order to leave the tube, the molecules must be acted on by a repulsive force, which is exerted by other gas molecules entering at the other end. The dynamics of these various nonequilibrium diffusion regions are characterized and will be discussed in detail. In addition, a discussion of how the results change with changes in nanotube chirality and diameter will be discussed. This work is supported by the NASA Ames Research Center.