Modeling of water molecules flow through carbon nanotubes with different temperatures, external forces and charges

• Main Author: Jiang, Yige
• Other Authors: Li Changming
• Format: Final Year Project
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering::Nanotechnology
• Online Access: http://hdl.handle.net/10356/16458
• Institution: Nanyang Technological University

Carbon nanotubes have become meaningful researching target since around two decades due to their great importance to both the applications and theoretical studies. In respect that carbon nanotubes are very costly, researchers usually use Molecular Dynamics to simulate the experiments on computers. Among various researching aspects, water flowing through the CNTs is a hot topic in the area of CNTs studying due to its great value in modeling the real biological or chemical phenomenon. In this project, efforts have been put in investigating how the external factors such as external forces, different temperatures and various dipole or charges influence the flowing activity of water molecules through the CNTs. From the results and analysis obtained, some conclusions can be made that 1) Without any external force, the only driven force that leads to the water molecule movement is the thermo energy; the Van der Waals force between the water molecules and carbons, together with the dipole-dipole interactions of water-water and water-carbon, keeps the one directional alignment of the water structure in the CNTs. 2) Once applied with external forces, the water molecules in the CNTs gained free energy to change their aligning structure, and the net flow also increases. Though not proportional, the external force and net flow show strongly positive correlation in a certain range. One observation that is worth noting is that, due to the existence of the energy barrier of water losing H-bond to enter the CNTs, when the applied external force is relatively low (below a critical value), the net flow doesn’t change a lot when the external force increases. 3) Different temperatures influence the flowing activity by change the total energy of the water molecules, and the temperature and the net flow are strongly positively correlated. The reason of the appearance of plateaus on the temperature-net flow curve needs to be found out in further researches. 4) The charges/dipole added on the CNTs changes both the water alignment and the net flow by the Coulomb interaction, and the more the CNTs are charged, the larger the change will be. Also, it should be noted that all of the simulations in this project are ran in (6,6) CNTs, with a TIP3 water model and some specific parameters. Since the mechanical and chemical properties vary from different sizes and types of CNTs, and the interactions are different under different settings, the results and conclusions obtained in this project may not be true in other cases. Additionally, for the future research, similar simulations are needed for different water models and parameters to verify the effect of these external factors, and trials with larger size of CNTs are also needed to explore the secret of the CNTs.