Design And Mechanism Study Of Nanopump Based On Carbon Nanotube

Actuation of a fluid flow in the nanopores is of fundamental importance for the progress in design and utilization of novel nanofluidic devices, machines and sensors, which has a broad prospect of potentially industrial applications including nanofiltration, water purification, and hydroelectric power generation. It has been recognized that the active transport of water through nanopores is technically difficult or even impossible using conventional methods due to the large surface to volume ratio, though there are various kinds of devices applied to pump water conveniently on macroscopic level. Therefore, it is crucial to develop effective water pump devices which can make a continuous unidirectional water flow on nanoscale.We proposed a blueprint for nanosized water pumps based on carbon nanotubes. This thesis focused on the mechanism behind the unidirectional water flow through carbon nanotubes and the effects of outside signals (electrical or mechanical signals) on the unidirectional water, including the impact of the charge size on the nanotube on the diffusion properties of the inner water, the interesting resonant phenomenon and current inversions in the nanosized water pump.Using molecular dynamics simulations, we have investigated the impact of the ice-like water monolayer inside the tube and nearest to the tube wall on the diffusion properties of other inner water shells confined within a charged nanotube. We find that the diffusion coefficients increase when the charge is larger than a critical value qc. This unexpected phenomenon is attributed to the first ice-like monolayer induced by the larger sized charge and the decreased number of hydrogen bonds between the first monolayer and other inner water shells caused by the very unique hydrogen-bond network patterns in the first ice-like monolayer, which makes it behave like a "hydrophobic water layer".The directed transport of water molecules in a single-walled carbon nanotube (SWNT), when the system is driven away from thermal equilibrium by an additional deterministic perturbation of a vibrating charge and the spatial inversion symmetry is broken by the continuous deformations of the SWNT, is studied via molecular dynamics simulations. The water flux almost increases linearly within a deformation of 1.9 A but decreases sharply for a further deformation of 0.6 A. The mechanism behind these interesting phenomena is studied by calculating the average interactions between water molecules inside the tube and the vibrating charge and the carbon nanotube in detail.In the study of the unidirectional flow through the naosized water pump, a resonance-like phenomenon is found. We pay attention to the effect of rotating frequency of the charge on the pumping ability. The water flux across the SWNT increases with respect to the rotating frequency of the external charge and reaches the maximum when the frequency is 4 THz. The mechanism behind the resonant phenomenon has been explained by the theory of classical harmonic oscillators.We investigate current inversions in three nanosized water pumps based on carbon nanotubes with different size powered by mechanical vibration. It was found that the water current depended sensitively on the frequency of mechanical vibration and underwent reversals of the water current. We found the conditions required to produce rapid directed transport of water through the carbon nanotube. The first factor is that the frequency of mechanical vibration is in the resonance region of water molecules confined in the carbon nanotube. The second factor is that there is an obvious difference in vibration amplitude between the two surface waves propagating toword to each end of the carbon nanotube. And current inversions is attributed to the dynamics competition of the water molecules in the two sections(the left and right parts) divided by the vibrating atom and the differences in phase and decay between the two mechanical waves generated by mechanical vibration and propagating in opposite directions toward the two ends of the carbon nanotube.Our findings provide an insight to water transportation through nanochannals and have potential in the design of high-flux nanofluidic device and nanocale energy converters.