Lateral electric field promotes the water transport in double-walled carbon nanotubes

Abstract

A lateral electric field typically impedes the water transport in single-walled carbon nanotubes (SWCNTs), because it disrupts the hydrogen bond network among confined water molecules. In this work, through a series of molecular dynamics simulations, we observe an opposite phenomenon in double-walled carbon nanotubes (DWCNTs): the lateral electric field promotes the water transport. The underlying mechanism is that the hydrogen bond network can be partially breakdown by the lateral electric field, thereby melting the ice-like structures in DWCNTs, which facilitates water transport. Meanwhile, for the confined cylinder monolayer water, enhanced rotational motion under stronger field strengths can be more efficiently converted into translational motion. Specifically, as the field strength increases, the water flow increases almost linearly, corresponding to the decay in hydrogen bond number. With the increase in CNT length, the water flow exhibits a linear reduction and reaches completely zero at weak field strengths because of the formation of ice structures in long CNTs. Some other parameters, such as translocation time, occupancy number, and dipole and density distributions also show a specific dependence on the field strength and CNT length. These findings enrich our understanding of the unusual dynamics of water molecules in DWCNTs and shed light on a new idea for the design of novel nanofluidic devices.