Manipulation of Long-Range Water Ordering in Less Confined Nanotubes

It is well-known that the short-range correlation among water molecules can extend up to no more than three hydration layers in bulk, whereas the long-range water-water correlation was only observed under extreme confinement. Here, we report an unexpected long-range orientational correlation of water molecules confined in relatively wider carbon nanotubes for the first time. Molecular dynamics simulations, including both charge-dipole and dipole-dipole interactions, show that the ordering correlation can be dramatically enhanced by an external dipole, although the enhancement decreases with increasing tube width. The external dipole, namely, the imposed point charges, can trigger the reorientation of the less confined water molecules, and the manipulation does not decay along the axial direction, at least in the simulated range. The long-range correlation and reorientation of water molecules in less confined nanotubes should have wide implications in both water-related biological systems and molecular-scale signaling.