M.Sc Student | Tali Mutat |
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Subject | Atomistic Simulation of Diffusion and Separation of Small Molecules in Carbon Nanotubes |

Department | Department of Physics |

Supervisors | Dr. Adler Joan |

Professor Emeritus Sheintuch Moshe | |

Full Thesis text |

The transport of gas mixtures through inorganic membranes, such as carbon nanotubes, is a subject of great current interest in chemical industries. The understanding of the molecular transport in carbon nanotubes is still largely incomplete. This is due to the fact that a wide variety of factors, such as the nanotube structure and diameter, the molecule dimensions and the temperature of the gas, contribute to the overall transport properties. Therefore, computational methods, such as molecular dynamics or Monte Carlo simulations are used to determine transport mechanisms inside nanotubes.

We apply the molecular dynamics method to investigate the self
diffusion of CH_{4} under macroscopic equilibrium through single wall
carbon nanotubes (SWNTs). For this purpose, an empirical many-body classical
potential, (the reactive bond order (REBO) potential), was chosen for modeling
the covalent bonding between the carbon
atoms of the SWNT as well as the tetrahedral structure of the diffusive
molecules. Values of self diffusion coefficient, *D _{s}*, decrease
with increased loading. A non-equilibrium molecular dynamics method is
implemented to study transport diffusion of CH

We present transport probability results for CH_{4},
N_{2} and H_{2} diffusing as pure components or in binary and
triple mixtures through narrow SWNTs as a function of counter diffusion of
molecules transporting in the opposite direction. The transport probability
decreases as the counter diffusion increases. The transport probabilities of CH_{4}
and N_{2} were considerably diminished due to mutual inhibition, whereas
the transport probability of H_{2} diffusing in a binary or ternary
mixture was found to be only slightly lower than the values for H_{2}
diffusing as a single component. The model based on single-file transport
theory yields predictions of the transport probability in good agreement with
the simulation results of CH_{4} and N_{2.} The differences
between the characteristics of the diffusive gases are found to be critical for
the separation efficiency of a SWNT.