Controlling Water Flow in Pattern-Charged Nanotubes

Molecular dynamics simulation is used to study the water flow in a charged nanotube. The simulation results show that the charge patterns on the nanotube have an important role in determining the flow behavior. In a nanotube charged with one pattern, the water flow rate decreases with increasing charge value, when the charge value increases from 0 to 0.8 e, the water flow rate decreases to 7%. While in the other one with a different charge pattern, the water flow rate is independent of charge value. By analyzing the morphology of water molecules, it is determined that this unexpected phenomenon is caused by the structure of water molecules near the nanotube wall. For the first charge pattern, the network of hydrogen bonds formed by water molecules near the wall had a hexagonal structure, similar to single layer ice, which changes the interactions between the wall and the water molecules. By contrast, the second pattern did not exhibit such an effect. This study provides a means to control the rate of water flow in nanotubes using an electric field. These results may provide new insights and lead to new methods for flow control in complex micro- or nanofluidic systems.