Structural and dynamic properties of water molecules in a uniformly charged nanopore

The structural and dynamic properties of water molecules in a uniformly charged nanopore have been studied using the method of classical molecular dynamics simulation. When confined in an uncharged nanopore with an appropriate radius, water molecules are aligned along the nanopore axis and form a single-file structure with the dipole vectors pointing toward the same end of the nanopore. We demonstrate here that when the nanopore is uniformly charged, the water molecules in the nanopore pack more tightly and the water molecules near the two ends of the nanopore are no longer aligned along the nanopore axis but tend to be aligned perpendicularly to the nanopore axis. The water dipole vectors do not point toward the same nanopore end. When the nanopore is positively charged, the water molecules in the nanopore align with their oxygen atoms pointing to the center of the nanopore. The central water molecule forms an L-defect. However for a negatively charged nanopore, the water molecules in the nanopore take up the opposite orientation. A D-defect is formed at the center of the nanopore. Furthermore, the water molecules in the negatively charged nanopore with moderate atomic partial charges diffuse and transport more quickly than the water molecules in an uncharged nanopore.