Transport Diffusion through Carbon Nanotube

In the simulation, the nanotube (which is the flow region) is bounded by two control volumes (CV) at the edges to study chemical-gradient driven diffusion. The chemical potential in each CV is fixed by inserting and deleting particles-Grand Canonical Monte Carlo (GCMC phase), and the dynamic motion is described by Molecular Dynamics (MD). Simulation of methane molecules diffuse inside a rigid/flexible (6,6) carbon nanotube, radius 4.07Å and length 100Å at 600 K. The visualizations were made using the program, AViz1.


The densities of the following control volumes are: ρ*cv1=0.25, ρ*cv2=0.01. A methane molecule is colored green when it crosses the rigid tube and enters the left control volume cv2. At CV1=200 molecules, CV2=10 molecules
mpeg format



The following simulation is a continuation of the above one, here we can see the adsorption stage:
mpeg format



The following simulation describes a simulation initially with one methae molecule with velocity 0, at the center of the tube, since the tube is flexible, the vibrate carbon atoms transfer energy to the methane molecule. CV1=200 molecules, CV2=10 molecules:
mpeg format



The following simulation describes a similar simulation (flexible tube) to the last one initially with one methae molecule with velocity 0 at the center of the tube, here CV1=27 molecules and CV2=10 molecules. Can not detect here adsorption as in the last simulation due to low pressure gradient at the control volumes.
mpeg format



Here the simulation describes a rigid tube initially with one methae molecule with velocity 0, CV1=27 molecules and CV2=10 molecules. The methane molecule stuck until other molecule hits it, in a ballistic motion, transfer almost all its momentum, and get stuck (but still vibrate) until other molecule hits it. Also here can not detect here a meaningful adsorption.

mpeg format



Here is a different simulation, both control volumes has the same densities (40 methane molecules), CV1 with red atoms, CV2 with green atoms. When atom is created (with the GCMC phase) in CV1 it colored red and in CV2 it colored green
mpeg format



Here is a continuation simulation to last one, after 1.3 ns from the start of the simulation. The system reaches a steady state after relatively short time, here is the flux vs. time of this simulation
mpeg format

1 J. Adler, A. Hashibon, N. Schreiber, A. Sorkin, S. Sorkin and G. Wagner, "Visualization of MD and MC Simulation for atomistic Modeling", Computer Physics Communication, (2002) 147, 665-9