HEDPS, Center for Applied Physics and Technology, Department of Mechanics and Engineering Science, College of Engineering, Peking University, Beijing 100871, China.
J Chem Phys. 2013 Sep 21;139(11):114701. doi: 10.1063/1.4821151.
Using molecular dynamics simulations, we investigate the pressure-driven water infiltration behavior of carbon nanotubes (CNTs), in which water molecules can infiltrate into CNTs from outside upon an external impact load. According to the direction of impact mechanical wave, the infiltration procedure can be divided into the forward stage (stage I) and the reflected stage (stage II). At the forward stage of mechanical wave, the flow behavior strongly depends on the impact velocity but it is essentially not very sensitive to the tube radius. With a higher impact velocity, the water flow has a higher transport velocity, a lower density, a weaker CNT-water interaction, a higher potential energy, and a more disordered structure shown by a wider distribution of water dipole and OH bonds orientations. At the reflected stage, due to the impact pressure effect, the water structure is significantly changed, and the flow behavior is less sensitive to the impact velocity but more sensitive to the tube radius. After the reflected wave passed the water molecules inside CNTs, the water density and potential are significantly increased, which initiates a significant change for the water structure inside CNTs, especially for small size tubes. In a small tube like (10,10), a new water conformation is created in the reflected procedure, while there is no such new structure created in a larger tube like (20,20). Due to the different structures, the behavior of the pressure-driven water flow inside CNTs is significantly different than the steady flow.
利用分子动力学模拟，研究了在外部冲击载荷作用下，水分子从外部渗透进入碳纳米管（CNT）的压力驱动水渗透行为。根据冲击力学波的方向，渗透过程可以分为前向阶段（阶段 I）和反射阶段（阶段 II）。在机械波的前向阶段，流动行为强烈依赖于冲击速度，但对管半径的影响本质上并不显著。随着冲击速度的增加，水流具有更高的传输速度、更低的密度、更弱的 CNT-水相互作用、更高的势能以及更无序的结构，表现为水偶极和 OH 键取向的分布更宽。在反射阶段，由于冲击压力的影响，水结构发生显著变化，流动行为对冲击速度的敏感度降低，但对管半径的敏感度增加。反射波通过 CNT 内部的水分子后，水的密度和势能显著增加，这引发了 CNT 内部水结构的显著变化，特别是对于小尺寸的管。在像（10,10）这样的小管中，在反射过程中会产生一种新的水构象，而在较大的管如（20,20）中则不会产生这种新结构。由于结构的不同，压力驱动的 CNT 内部水流行为与稳态流动有显著差异。
