Chen Shuai, Cheng Yuan, Zhang Gang, Zhang Yong-Wei
Institute of High Performance Computing, ASTAR 138632 Singapore
Nanoscale Adv. 2018 Dec 21;1(3):1175-1180. doi: 10.1039/c8na00322j. eCollection 2019 Mar 12.
Controlling water molecular motion at the nanoscale is critical for many important applications, such as water splitting to produce hydrogen and oxygen, biological and chemical cell reactions, nanofluidics, drug delivery, water treatment, In this paper, we propose a new nanoscale device based on carbon nanotubes (CNTs) with a stiffness gradient to create a spontaneous directional motion of water molecules, and perform molecular dynamics simulations to analyze its transport characteristics. We find that the (6, 6) CNT possesses an optimal water transport rate. In the thinner CNTs, the water molecules are strongly confined by the CNT wall, resulting in a higher friction force; while in the thicker CNTs, the driving force is lower, and the water molecules tend to form ring-like configurations, resulting in a slower motion. For the (6, 6) CNT, water molecules tend to favor a chain-like configuration, through which the molecules are able to move synergistically along the stiffness gradient, and the transportation efficiency increases with the stiffness gradient but decreases with temperature. Both energetic and kinetic analyses are performed to elucidate this fascinating directional motion. Our work demonstrates a new strategy for controlling water molecular motion at the nanoscale without resorting to any active driving source, such as electric field, temperature or pressure difference.
在纳米尺度上控制水分子运动对于许多重要应用至关重要，例如水分解制氢和氧、生物和化学细胞反应、纳米流体、药物递送、水处理等。在本文中，我们提出了一种基于具有刚度梯度的碳纳米管（CNT）的新型纳米器件，以产生水分子的自发定向运动，并进行分子动力学模拟来分析其传输特性。我们发现（6,6）碳纳米管具有最佳的水传输速率。在较细的碳纳米管中，水分子受到碳纳米管壁的强烈限制，导致摩擦力较高；而在较粗的碳纳米管中，驱动力较低，水分子倾向于形成环状结构，导致运动较慢。对于（6,6）碳纳米管，水分子倾向于形成链状结构，通过这种结构分子能够沿着刚度梯度协同移动，并且传输效率随刚度梯度增加而增加，但随温度降低。我们进行了能量和动力学分析以阐明这种引人入胜的定向运动。我们的工作展示了一种在纳米尺度上控制水分子运动的新策略，而无需借助任何有源驱动源，如电场、温度或压差。
