中国物理B ›› 2012, Vol. 21 ›› Issue (5): 54703-054703.doi: 10.1088/1674-1056/21/5/054703

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Asymmetry of the water flux induced by the deformation of a nanotube

何俊霞1,陆杭军1,刘扬2,吴锋民1,聂雪川1,周晓艳1,陈艳燕1   

  1. 1. Department of Physics, Zhejiang Normal University, Jinhua 321004, China;
    2. Department of Mechanical Engineering, the Hong Kong Polytechnic University, Hong Kong, China
  • 收稿日期:2011-09-09 修回日期:2012-04-27 出版日期:2012-04-01 发布日期:2012-04-01
  • 基金资助:
    Project supported by the National Natural Science Foundation of China (Grant Nos. 11005093, 10932010, and 10972199), the Zhejiang Provincial Natural Science, China (Grant Nos. Z6090556, Y6100384, and Y607425), the Zhejiang Provincial Education Department, China (Grant No. Y200805556), and the Hong Kong Polytechnic University, China (Grant No. G-YG84).

Asymmetry of the water flux induced by the deformation of a nanotube

He Jun-Xia(何俊霞)a), Lu Hang-Jun(陆杭军) a)†, Liu Yang(刘扬)b), Wu Feng-Min(吴锋民)a), Nie Xue-Chuan(聂雪川)a), Zhou Xiao-Yan(周晓艳) a), and Chen Yan-Yan(陈艳燕)a)   

  1. a. Department of Physics, Zhejiang Normal University, Jinhua 321004, China;
    b. Department of Mechanical Engineering, the Hong Kong Polytechnic University, Hong Kong, China
  • Received:2011-09-09 Revised:2012-04-27 Online:2012-04-01 Published:2012-04-01
  • Supported by:
    Project supported by the National Natural Science Foundation of China (Grant Nos. 11005093, 10932010, and 10972199), the Zhejiang Provincial Natural Science, China (Grant Nos. Z6090556, Y6100384, and Y607425), the Zhejiang Provincial Education Department, China (Grant No. Y200805556), and the Hong Kong Polytechnic University, China (Grant No. G-YG84).

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摘要： The behavior of nano-confined water is expected to be fundamentally different from the behavior of bulk water. At the nanoscale, it is still unclear whether water flows more easily along the convergent direction or the divergent one, and whether a hourglass shape is more convenient than a funnel shape for water molecules to pass through a nanotube. Here, we present an approach to explore these questions by changing the deformation position of a carbon nanotube. The results of our molecular dynamics simulation indicate that the water flux through the nanotube changes significantly when the deformation position moves away from the middle region of the tube. Different from the macroscopic level, we find water flux asymmetry (water flows more easily along the convergent direction than along the divergent one), which plays a key role in a nano water pump driven by a ratchet-like mechanism. We explore the mechanism and calculate the water flux by means of the Fokker--Planck equation and find that our theoretical results are well consistent with the simulation results. Furthermore, the simulation results demonstrate that the effect of deformation location on the water flux will be reduced when the diameter of the nanochannel increases. These findings are helpful for devising water transporters or filters based on carbon nanotubes and understanding the molecular mechanism of biological channels.

关键词: single-walled carbon nanotube, deformation position, molecular dynamics simulation, water flux

Abstract: The behavior of nano-confined water is expected to be fundamentally different from the behavior of bulk water. At the nanoscale, it is still unclear whether water flows more easily along the convergent direction or the divergent one, and whether a hourglass shape is more convenient than a funnel shape for water molecules to pass through a nanotube. Here, we present an approach to explore these questions by changing the deformation position of a carbon nanotube. The results of our molecular dynamics simulation indicate that the water flux through the nanotube changes significantly when the deformation position moves away from the middle region of the tube. Different from the macroscopic level, we find water flux asymmetry (water flows more easily along the convergent direction than along the divergent one), which plays a key role in a nano water pump driven by a ratchet-like mechanism. We explore the mechanism and calculate the water flux by means of the Fokker--Planck equation and find that our theoretical results are well consistent with the simulation results. Furthermore, the simulation results demonstrate that the effect of deformation location on the water flux will be reduced when the diameter of the nanochannel increases. These findings are helpful for devising water transporters or filters based on carbon nanotubes and understanding the molecular mechanism of biological channels.

Key words: single-walled carbon nanotube, deformation position, molecular dynamics simulation, water flux

中图分类号:  (Micro- and nano- scale flow phenomena)

  • 47.61.-k
89.40.Cc (Water transportation) 05.40.-a (Fluctuation phenomena, random processes, noise, and Brownian motion) 61.20.Ja (Computer simulation of liquid structure)