Controllable Transport Of Water Through Carbon Nanotube

In recent years,nanofluidic devices have attracted much attention due to their potential applications in industry,biology,and medicine.The key to designing and applying nanofluidic devices is achieving regulated water transport within nanochannels.While the regulated transport of water at the macroscopic scale is simple enough,regulating water at the micro-nano scale remains difficult.Therefore,studying the regulated transport of water within nanochannels is particularly important.In this thesis,molecular dynamics methods are used to study the phenomena regarding water molecules in carbon nanotubes produced in electric fields.For example: the regulated transport of water by nanogap,electric field,and cnt size;the regulated transport of water by the combination of pressure difference and electric field;and the regulated transport of gas(methane)mixed with water in the cnt in the presence of ethe lectric field.Firstly,the water transport process in carbon nanotubes containing nano-gaps(disjoint carbon nanotubes)under the effect of the vertical electric field is investigated in this thesis.With the increase of the vertical electric field,the water transport rate,water adsorption,water mobility,and water orientation of carbon nanotubes with nanogaps decreased more rapidly than those without nano-gaps.The vertical electric field affects the water transport properties by influencing the formation of water bridges in the nano-gap region.Secondly,the transport processes of water molecules in disjoint carbon nanotubes with different diameters under the effect of vertical electric fields were investigated.It was found that when the vertical electric field increased from 0 V/nm to 1.0 V/nm,the water molecule transport capacity inside the large-diameter disjoint carbon nanotubes decreased significantly,while the water molecule transport capacity inside the smalldiameter disjoint carbon nanotubes decreased insignificantly.Again,the water transport properties through short carbon nanotubes under the influence of pressure difference and electric field were investigated.It was found that the bidirectional water transport rate of carbon nanotubes without an electric field was insensitive to the pressure difference,while the unidirectional water transport rate was sensitive to the pressure difference.Under the same pressure difference,the bidirectional water transport rate of carbon nanotubes increases rapidly with the increase of carbon nanotube diameter,while the unidirectional transport is opposite to the bidirectional transport result.Under the influence the of electric field,the unidirectional transport efficiency of water in short carbon nanotubes was improved.The results of this study provide a reference for regulating the unidirectional transport of water within the nanotube channel.Water transport in nonaligned disjoint carbon nanotubes was then investigated.It was found that the water transport capacity decreased with the increase in the vertical separation distance of the nonaligned disjoint carbon nanotubes.Due to the disappearance of water bridges,water molecules could not be transferred through the nonaligned disjoint carbon nanotubes when the vertical distance of non-coaxially cleaved carbon nanotubes reached 0.42 nm.This finding contributes to a deeper understanding of the behavior of water in nonaligned disjoint carbon nanotubes.Finally,the adsorption and transport properties of methane-water mixtures in carbon nanotubes under the influence of electric fields were investigated.The strength and direction of the electric field affect the adsorption and transport order of water and methane in carbon nanotubes,and once the carbon nanotubes are filled with methane(or water)molecules,the transport of other molecules is blocked.The adsorption process of methane or water molecules in carbon nanotubes can be reversed by turning on or off the electric field to achieve adsorption and transport,and the results of the study are important for the tunable transport in the nanochannel.