Molecular insights into water flow in double-walled carbon nanotubes with annular confinement

The structure of a channel significantly influences the structure and dynamic behavior of water in confined systems. In this work, we investigate the flow behavior within the interlayer of double-walled carbon nanotubes (DWCNTs) using molecular dynamics (MD) simulations. We also examine the flow velocities under different water structures and specific extreme conditions to understand their impact. Notably, when an identical pressure gradient drives water, the flow velocity within DWCNTs exceeds that between graphene slabs when the channel width is below 0.88 nm. Beyond 0.88 nm, the opposite trend occurs, with water flowing faster between graphene slabs. The difference in friction coefficients between the inner and outer wall of the DWCNT, along with changes in water molecule distribution and water structure as the channel width varies, causes this divergence in flow velocities. Further analysis of diffusion coefficients, depletion lengths, and water configurations provides deeper insights into the underlying differences in flow characteristics. These findings offer valuable guidance for the design and optimization of nanofluidic devices.