Hanasaki Itsuo, Nakatani Akihiro
Department of Adaptive Machine Systems, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
J Chem Phys. 2006 Apr 14;124(14):144708. doi: 10.1063/1.2187971.
We have conducted molecular dynamics simulations of water flow in carbon nanotubes (CNTs) for (6,6) to (20,20) CNTs at a streaming velocity of 100 ms. The fluidized piston model (FPM) and the ice piston model (IPM) are employed to drive flow through the CNTs. The results show that the single-file water flow inside (6,6) CNT has a convex upward streaming velocity profile, whereas the velocity profiles in (10,10) to (20,20) CNTs are flat except near the tube wall. The flow structure of cylindrical water in the (8,8) CNT is intermediate between that for the (6,6) CNT and the larger CNTs. The flow parameters are found not to exhibit any dependence on streaming velocity at up to 300 ms in the (12,12) CNT. The hydrogen bond lifetimes of water flowing in CNTs tend to be longer than for the corresponding equilibrium states, and nonzero flow does not reduce the microscopic structure or structural robustness (hydrogen bond lifetime). Although the atomic density profile varies with tube diameter, reflecting the change in static microscopic structure of flow from single file to cylindrical, tube diameter does not induce a clear transition in streaming velocity, temperature, or hydrogen bond lifetime over this diameter range. The results suggest that water flow in CNTs of this size is more pluglike than Poiseuille type, although the flow structure does not strictly accord with either definition.
我们对碳纳米管（CNT）中（6,6）至（20,20）碳纳米管内水流进行了分子动力学模拟，流速为100米/秒。采用流化活塞模型（FPM）和冰活塞模型（IPM）驱动水流过碳纳米管。结果表明，（6,6）碳纳米管内的单列水流具有向上凸起的流速分布，而（10,10）至（20,20）碳纳米管内的流速分布除靠近管壁处外是平坦的。（8,8）碳纳米管内圆柱形水流的流动结构介于（6,6）碳纳米管和较大碳纳米管之间。发现在（12,12）碳纳米管中，流速高达300米/秒时，流动参数对流速没有任何依赖性。碳纳米管内流动水的氢键寿命往往比相应平衡态的氢键寿命长，且非零流动不会降低微观结构或结构稳健性（氢键寿命）。尽管原子密度分布随管径变化，反映了从单列到圆柱形流动的静态微观结构变化，但在该直径范围内，管径不会在流速、温度或氢键寿命上引起明显转变。结果表明，这种尺寸的碳纳米管内的水流比泊肃叶型水流更像栓塞流，尽管流动结构并不严格符合任何一种定义。
