Department of Applied Physics, Nanjing University of Science and Technology, Nanjing, Jiangsu 210094, People's Republic of China.
Nanotechnology. 2019 Jun 14;30(24):245707. doi: 10.1088/1361-6528/ab0cd7. Epub 2019 Mar 5.
The transport of water through carbon nanotubes (CNTs) is now of great importance in bionanotechnology and of considerable interest for potential nanofluidic applications. In this paper, we show by molecular dynamics simulations that the permeation of single-file water molecules through a CNT can be significantly improved by means of tuning the direction of pressure difference, i.e. introducing an additional lateral pressure to the longitudinal one. The water flow exhibits an interesting maximum behavior with the change of lateral pressure, deciphered by the breakdown of single-file water chain inside the CNT. The translocation time decreases monotonously with the increase of lateral pressure and exhibits a clear bifurcation due to the longitudinal pressure, corresponding to the flow enhancement. Therefore, the lateral pressure will increase the difficulty for water entering, while promotes the water conduction inside the CNT, whose competition ultimately leads to the flow maximum behaviors. Along with the water reducing inside the CNT, the CNT switches between the filling and empty states with the unique distributions of water dipole orientation, density and H-bond number. Our results indicate that tuning the direction of pressure difference should be a significant new strategy for enhancing the water permeability, where the key lies in the breakdown of single-file water chain and are thus insightful for future studies.
水在碳纳米管（CNTs）中的传输在生物纳米技术中具有重要意义，并且对于潜在的纳流控应用也具有相当大的兴趣。在本文中，我们通过分子动力学模拟表明，通过调节压力差的方向（即对纵向压力施加额外的横向压力）可以显著提高单分子水通过 CNT 的渗透率。水的流动表现出有趣的最大行为，这与 CNT 内单分子水链的断裂有关。随着横向压力的增加，迁移时间单调减少，并且由于纵向压力而出现明显的分岔，这对应于流动增强。因此，横向压力会增加水进入的难度，同时促进 CNT 内的水传导，两者的竞争最终导致了流动的最大行为。随着 CNT 内的水减少，CNT 在填充和空状态之间切换，具有独特的水偶极取向、密度和氢键数的分布。我们的结果表明，调节压力差的方向应该是增强水渗透性的一个重要新策略，其关键在于单分子水链的断裂，因此对未来的研究具有启发性。
