Faster Diffusion of Water along Carbon Nanotubes near the Wall

The diffusion of water in carbon nanotubes (CNTs) is debated, particularly whether it is faster near the CNT wall or at the center and how the temperature influences this effect. Using molecular dynamics (MD) simulations, we study radially resolved water diffusion in CNT(26,26) (3.57 nm diameter) over a wide temperature range. Diffusion along the CNT axis is significantly enhanced compared to that of bulk water, with the effect intensifying at lower temperatures. Supercooling further amplifies this enhancement following near-Arrhenius behavior. Confinement has a smaller impact on the rotational dynamics. By resolving water motion into radial layers, we find that both translational and rotational dynamics are higher near the CNT wall due to weakened hydrogen bonding. The presence of dangling O-H bonds reduces friction at the CNT-water interface. Revisiting an NMR study, we suggest that the high-intensity peak corresponds to central layers, aligning with our MD results and refining our insights into confined water dynamics.