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Study of directional transmission of carbon nanotube water molecules

Author: ChenGuiHu
Tutor: LuoChengLin
School: Nanjing Normal University
Course: Condensed Matter Physics
Keywords: Carbon nanotubes molecular dynamics simulation water pump orientationof water dipole flipping flipping period
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Type: Master's thesis
Year: 2013
Downloads: 57
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Abstract


Due to the outstanding properties,Carbon Nanotubes (CNTs) have become the artificial ion channels. It has great significance to study microstructures and transport properties of confined water within carbon nanotubes (CNTs) by using Molecular Dynamics (MD) Simulation for understanding the conduction mechanism of confined molecules within biological water channel,together with the structure and function of biological systems and designing novel molecular devices,machines,including the desalination of seawater.The content of the research presented in this paper contains two major parts:in the first part,based on the the double-wall carbon nanotubes (DWCNTs)model (see figure4.1), we investigate the effects of moving outer tube at different velocities on the transport properties of single-file water molecules through inner nanotubes by using molecular dynamics simulation. We find that the PMF(the potential of mean forces) and orientation of water molecules inside the CNT can be well-tuned by moving outer tube and is strong coupled to the water flux. This orientation-induced water flux is due to the traction and the asymmetrical water-water interaction along the CNT axis. Most importantly, a critical velocity vc related to the frequency of flipping for the water dipoles and the water flux is found. The frequency of flipping and the water flux are increased as v is increased for0<v≤vc while decreased for vc<v≤10m/s. Thus, The movement of outer rube along z axis will trigger the unidirectional flow of water molecules,which provides a route for designing novel nanopumps.In the second part, base on the model (as shown in Fig.5.1), we simulate the flipping of water dipoles inside the (5,5)and (6,6)single-walled carbon nanotubes(SWCNT)with different lengths. We find that the water dipoles inside the SWCNT can flip in the form of zipper-like. In addition, in our system, the flipping period of water dipoles can be linearly increase with the length of SWCNT, and the average flipping period in (5,5)SWCNT is bigger than in (6,6)SWCNT at the same length. Meanwhile,the flipping time of water dipoles and the average flipping time of a single water dipole are increased as the length of the SWCNT is increased,while are decreased as the radius of the SWCNT is increased.The reasons are found. The average potential barrier against flipping increases as the length of SWCNT increases and the average potential barrier against flipping in (5,5)SWCNT is bigger than in (6,6)SWCNT at the same length.

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