Electric Field Modulation of Water Transport in Carbon Nanotubes: Insights from Molecular Dynamics Simulations

At the nanoscale, fluid transport properties exhibit notable deviations from those observed at the macroscale. The flow dynamics of these fluids are influenced by various factors, including electric fields, pressure gradients, and intermolecular interactions. Although the transport of polar molecules, such as water, within nanochannels has been extensively investigated, the fundamental mechanisms within these channels─particularly the impact of electric fields on the unidirectional transport of fluids under a constant pressure differential─remain inadequately understood. Therefore, a deeper investigation into the effects of electric fields on fluid mass transport within nanochannels is crucial for achieving more precise control over fluid. This study employs molecular dynamics (MD) simulations to investigate the influence of electric fields on pressure-driven water transport through carbon nanotubes. The findings reveal that, under a parallel electric field, the stability of hydrogen bonds among water molecules within the carbon nanotubes is markedly improved, leading to a linear decrease in water flux with increasing electric field strength. Conversely, exposure to a perpendicular electric field induces nonlinear changes in water flux, with a significant reduction or complete cessation occurring once the electric field strength exceeds a certain threshold. This phenomenon occurs because the perpendicular electric field disrupts the hydrogen bonding network among water molecules in carbon nanotubes, thereby increasing the energy barrier for water molecules to traverse the nanotubes. Additionally, we investigate the influence of electric fields on the transport characteristics of heavy water (D2O), evaluating the variations in mass transfer for distinct isotopes of the same element. We found that the reduced flow rate of D2O within carbon nanotubes can be attributed to an increase in the density of hydrogen bonds present in D2O, coupled with a pronounced enhancement of the hydrogen bonding network. This augmentation contributes to a significant elevation in the energy barrier associated with the ingress of D2O into the carbon nanotubes. This study contributes to the understanding and design of carbon nanotubes for water molecule transport under electric field modulation.