Beijing National Laboratory for Molecular Sciences, Joint Laboratory of Polymer Sciences and Materials, State Key Laboratory of Polymer Physics and Chemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
ACS Nano. 2011 Jan 25;5(1):351-9. doi: 10.1021/nn1014616. Epub 2010 Dec 16.
The transport of water molecules through nanopores is not only crucial to biological activities but also useful for designing novel nanofluidic devices. Despite considerable effort and progress that has been made, a controllable and unidirectional water flow is still difficult to achieve and the underlying mechanism is far from being understood. In this paper, using molecular dynamics simulations, we systematically investigate the effects of an external electric field on the transport of single-file water molecules through a carbon nanotube (CNT). We find that the orientation of water molecules inside the CNT can be well-tuned by the electric field and is strongly coupled to the water flux. This orientation-induced water flux is energetically due to the asymmetrical water-water interaction along the CNT axis. The wavelike water density profiles are disturbed under strong field strengths. The frequency of flipping for the water dipoles will decrease as the field strength is increased, and the flipping events vanish completely for the relatively large field strengths. Most importantly, a critical field strength E(c) related to the water flux is found. The water flux is increased as E is increased for E ≤ E(c), while it is almost unchanged for E > E(c). Thus, the electric field offers a level of governing for unidirectional water flow, which may have some biological applications and provides a route for designing efficient nanopumps.
水分子通过纳米孔的传输不仅对生物活动至关重要，而且对于设计新型纳流道装置也很有用。尽管已经做出了相当大的努力和取得了进展，但仍然难以实现可控的单向水流，其背后的机制还远未被理解。在本文中，我们使用分子动力学模拟，系统地研究了外电场对单链水分子通过碳纳米管（CNT）传输的影响。我们发现，电场可以很好地调节 CNT 内水分子的取向，并且与水流强烈耦合。这种取向诱导的水流能量来源于 CNT 轴向上水分子之间的不对称相互作用。在强场下，波状的水分子密度分布会受到干扰。随着场强的增加，水分子偶极子的翻转频率会降低，而对于较大的场强，翻转事件会完全消失。最重要的是，我们发现了一个与水流相关的临界场强 E(c)。当 E ≤ E(c)时，随着 E 的增加，水流会增加，而当 E > E(c)时，水流几乎不变。因此，电场为单向水流提供了一种控制方式，这可能具有一些生物学应用，并为设计高效纳米泵提供了一种途径。
