Wu Yue, Wang Zi, Li Shuang, Su Jiaye
MIIT Key Laboratory of Semiconductor Microstructure and Quantum Sensing, and Department of Applied Physics, Nanjing University of Science and Technology, Nanjing 210094, China.
Phys Chem Chem Phys. 2024 Apr 3;26(14):10919-10931. doi: 10.1039/d4cp00007b.
Understanding the structures and dynamics of confined water in nanochannels holds great promise for various applications, ranging from membrane separation to blue energy collection. A setting of particular interest is the confined monolayer water within double-walled carbon nanotubes (DWCNTs), which demonstrates rich ice morphologies; however, the dynamics of this peculiar system are still unexplored. In this work, a series of molecular dynamics (MD) simulations reveal that the two-dimensional ice in DWCNTs can be effectively melted by terahertz electric fields but not by static electric fields, exhibiting an interesting ice to vapor-like transition along with extraordinary dynamical behaviors. Specifically, under appropriate field frequency, the water flow presents a sharp increase with the increase in field strength, indicating an excellent gating behavior. These remarkable findings are attributed to the resonance effect between the terahertz electric field and inherent vibration of water hydrogen bonds, causing the water molecules to change from the frozen to super permeation states. The amount of confined water exhibits a sudden reduction, confirming the breakdown of the hydrogen bond network. The distributions of density profiles, hydrogen bond number and dipole orientation demonstrate more details of the water structural change. Furthermore, under a certain field strength, the water flow shows a peculiar maximum behavior with the increase in field frequency, implying frequency optimization for water transport. These findings not only enhance our understanding of the phase transition behavior of water molecules confined within DWCNTs under the influence of a terahertz electric field but also provide a promising avenue for designing innovative nanofluidic devices.
了解纳米通道中受限水的结构和动力学对于从膜分离到蓝色能源收集等各种应用具有巨大的潜力。一个特别有趣的情况是双壁碳纳米管（DWCNT）内的受限单层水，它呈现出丰富的冰形态；然而，这个特殊系统的动力学仍未被探索。在这项工作中，一系列分子动力学（MD）模拟表明，DWCNT中的二维冰可以被太赫兹电场有效熔化，但不能被静电场熔化，呈现出从冰到类似蒸汽的转变以及非凡的动力学行为。具体而言，在适当的场频率下，水流随场强增加而急剧增加，显示出优异的门控行为。这些显著发现归因于太赫兹电场与水氢键固有振动之间的共振效应，导致水分子从冻结状态转变为超渗透状态。受限水的量突然减少，证实了氢键网络的破裂。密度分布、氢键数量和偶极取向的分布展示了水结构变化的更多细节。此外，在一定场强下，水流随场频率增加呈现出奇特的最大值行为，这意味着水传输存在频率优化。这些发现不仅增进了我们对太赫兹电场影响下DWCNT内水分子相变行为的理解，也为设计创新的纳米流体装置提供了一条有前景的途径。
