Salman Shabbir, Zhao Yunzhen, Zhang Xingke, Su Jiaye
Department of Applied Physics, Nanjing University of Science and Technology, Nanjing, Jiangsu 210094, China.
J Chem Phys. 2020 Nov 14;153(18):184503. doi: 10.1063/5.0028077.
Temperature governs the motion of molecules at the nanoscale and thus should play an essential role in determining the transport of water and ions through a nanochannel, which is still poorly understood. This work devotes to revealing the temperature effect on the coupling transport of water and ions through a carbon nanotube by molecular dynamics simulations. A fascinating finding is that the ion flux order changes from cation > anion to anion > cation with the increase in field strength, leading to the same direction change of water flux. The competition between ion hydration strength and mobility should be a partial reason for this ion flux order transition. High temperatures significantly promote the transport of water and ions, stabilize the water flux direction, and enhance the critical field strength. The ion translocation time exhibits an excellent Arrhenius relation with the temperature and a power law relation with the field strength, yielding to the Langevin dynamics. However, because of self-diffusion, the water translocation time displays different behaviors without following the ions. The high temperature also leads to an abnormal maximum behavior of the ion flux, deciphered by the massive increase in water flow that inversely hinders the ion flux, suggesting the coexistence of water-ion coupling transport and competition. Our results shed deep light on the temperature dependence of coupling transport of water and ions, answering a fundamental question on the water flux direction during the ionic transport, and thus should have great implications in the design of high flux nanofluidic devices.
温度控制着纳米尺度下分子的运动，因此在决定水和离子通过纳米通道的传输过程中应发挥重要作用，而目前对此仍知之甚少。这项工作致力于通过分子动力学模拟揭示温度对水和离子通过碳纳米管的耦合传输的影响。一个有趣的发现是，随着场强增加，离子通量顺序从阳离子>阴离子变为阴离子>阳离子，导致水通量方向发生相同的变化。离子水化强度和迁移率之间的竞争应该是这种离子通量顺序转变的部分原因。高温显著促进水和离子的传输，稳定水通量方向，并提高临界场强。离子转运时间与温度呈现出良好的阿伦尼乌斯关系，与场强呈现幂律关系，符合朗之万动力学。然而，由于自扩散，水的转运时间表现出不同的行为，与离子不同。高温还导致离子通量出现异常的最大值行为，这是由反向阻碍离子通量的水流大量增加所解释的，表明水-离子耦合传输和竞争并存。我们的结果深入揭示了水和离子耦合传输的温度依赖性，回答了离子传输过程中水通量方向的一个基本问题，因此对高通量纳米流体装置的设计应该具有重要意义。
