Electric Field\nModulation of Water Transport in Carbon\nNanotubes: Insights from Molecular Dynamics Simulations

At the nanoscale, fluid transport properties exhibit\nnotable deviations\nfrom those observed at the macroscale. The flow dynamics of these\nfluids are influenced by various factors, including electric fields,\npressure gradients, and intermolecular interactions. Although the\ntransport of polar molecules, such as water, within nanochannels has\nbeen extensively investigated, the fundamental mechanisms within these\nchannelsparticularly the impact of electric fields on the\nunidirectional transport of fluids under a constant pressure differentialremain\ninadequately understood. Therefore, a deeper investigation into the\neffects of electric fields on fluid mass transport within nanochannels\nis crucial for achieving more precise control over fluid. This study\nemploys molecular dynamics (MD) simulations to investigate the influence\nof electric fields on pressure-driven water transport through carbon\nnanotubes. The findings reveal that, under a parallel electric field,\nthe stability of hydrogen bonds among water molecules within the carbon\nnanotubes is markedly improved, leading to a linear decrease in water\nflux with increasing electric field strength. Conversely, exposure\nto a perpendicular electric field induces nonlinear changes in water\nflux, with a significant reduction or complete cessation occurring\nonce the electric field strength exceeds a certain threshold. This\nphenomenon occurs because the perpendicular electric field disrupts\nthe hydrogen bonding network among water molecules in carbon nanotubes,\nthereby increasing the energy barrier for water molecules to traverse\nthe nanotubes. Additionally, we investigate the influence of electric\nfields on the transport characteristics of heavy water (D<sub>2</sub>O), evaluating the variations in mass transfer for distinct isotopes\nof the same element. We found that the reduced flow rate of D<sub>2</sub>O within carbon nanotubes can be attributed to an increase\nin the density of hydrogen bonds present in D<sub>2</sub>O, coupled\nwith a pronounced enhancement of the hydrogen bonding network. This\naugmentation contributes to a significant elevation in the energy\nbarrier associated with the ingress of D<sub>2</sub>O into the carbon\nnanotubes. This study contributes to the understanding and design\nof carbon nanotubes for water molecule transport under electric field\nmodulation.