The Transport Behavior Of Water In The Nanotube With The Different Deformations

The transport properties of the water in the nano-confined space is related to some key issues, such as the biological metabolic metro and many physical, chemical fields and so on. It is important to understand the transport behaviors of water in the nanotube with different structures, which became to be the research focus for many fields near recent years. We know that the behavior of the water in the confined space is different to that in bulk, the dynamics processes of the water is affected by the scale, the structure and the material properties of the confined space. For example, the water molecules must automatically build up a single line before they go through the aquaporins. It is useful to help researchers understanding the transport properties and the kinetics of the water by explore the transport behavior of water in the different structure of nano-channel. So we think that our work is helpful for the researching in the biological channel and the designing of nanoscale devices for transportation.Although the discovery of carbon nanotube is very late, its development could be described by the word "fast". Carbon nanotube has been applied in various fields since been found since1991, including computer simulation of nanotubes. The carbon nanotube could be treated as the alternative of biological channel as some of its transport properties are similar as biological channel. So it is very important to understand and control the transport of water in carbon nanotubes for study the nano-channel and biological activity. We know it will cause a vapor-liquid transition or switch between open and closed when change the radius of the nanotube or the channel-water interaction is triggered. Here we change the deformation locations of carbon nanotubes to explore the switching characteristics of the narrow structure in the nano-channel.In this work, by using molecular simulation, we have analysised the transport behavior of water in the different deformation of carbon nanotubes. We predicted the transport mechanisms of water in the larger deformation of carbon nanotubes.The main work: Firstly, on the nanoscale, it is still unclear whether water flows more easily along the convergent direction than the divergent one, and whether a hourglass shape is more convenient than a funnel shape for water molecules to pass through a nanotube. This work, we changed the shape of the carbon nanotubes to explore these questions. Our simulation results of molecular dynamics indicate that the water flux through the nanotube changes significantly when the deformation position moves away from the middle region along the tube. Different from the macroscopiclevel, we find asymmetry of water flux (water flow more easily along the convergent direction than along the divergentone), which plays a key role in nano water pump driven by ratchet-like mechanism. We explore the mechanism and calculate the water flux by means of the Fokker-Planck equation and find that theoretical results are well consistent with the simulation results. Furthermore, simulation results demonstrate that the effect of deformation location on the water flux will be reduced when the diameter of nanochannel increases. These findings are helpful in devising the water transporter or filter based on carbon nanotubes and understanding the molecular mechanism of biological channels.