School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.
Department of General Surgery and Laboratory of General Surgery, Xinhua Hospital, Affiliated with Shanghai Jiao Tong University, School of Medicine, Shanghai 200092, China.
J Chem Phys. 2017 Oct 28;147(16):164705. doi: 10.1063/1.5000493.
Nanoconfinement environments are commonly considered advantageous for ultrafast water flow across nanotube membranes. This study illustrates that nanoconfinement has a negative effect on water transport across nanotube membranes based on molecular dynamics simulations. Although water viscosity and the friction coefficient evidently decrease because of nanoconfinement, water molecular flux and flow velocity across carbon nanotubes decrease sharply with the pore size of nanotubes. The enhancement of water flow across nanotubes induced by the decreased friction coefficient and water viscosity is markedly less prominent than the negative effect induced by the increased flow barrier as the nanotube size decreases. The decrease in water flow velocity with the pore size of nanotubes indicates that nanoconfinement is not essential for the ultrafast flow phenomenon. In addition, the relationship between flow velocity and water viscosity at different temperatures is investigated at different temperatures. The results indicate that flow velocity is inversely proportional to viscosity for nanotubes with a pore diameter above 1 nm, thereby indicating that viscosity is still an effective parameter for describing the effect of temperature on the fluid transport at the nanoscale.
纳米受限环境通常被认为有利于超快速水流通过纳米管膜。本研究基于分子动力学模拟表明，纳米受限对纳米管膜内的水输运具有负面影响。尽管由于纳米受限，水的粘度和摩擦系数明显降低，但水分子在碳纳米管中的通量和流速随纳米管的孔径急剧下降。由于摩擦系数和水粘度的降低而引起的纳米管内水流的增强，明显不如由于纳米管尺寸减小而引起的流动阻碍的增加所产生的负面影响显著。随着纳米管孔径的减小，水的流速降低表明纳米受限对于超快速流动现象并不是必需的。此外，还研究了不同温度下不同孔径纳米管中水的流速与粘度之间的关系。结果表明，对于孔径大于 1nm 的纳米管，流速与粘度成反比，这表明粘度仍然是描述纳米尺度下温度对流体输运影响的有效参数。
