The ice-like water monolayer near the wall makes inner water shells diffuse faster inside a charged nanotube

Abstract

Using molecular dynamics simulations, we have investigated the impact of the ice-like water monolayer inside the tube and nearest to the tube wall on the diffusion properties of other inner water shells confined within a charged nanotube. We find that the axial diffusion coefficient of the first water monolayer near the wall monotonously decreases with the charge size on the nanotube, indicating a tighter control of the first monolayer from the larger sized charge. However, for the other water shells, the diffusion coefficients increase when the charge is larger than a critical value qc (∼1.0 e). This unexpected phenomenon is attributed to the decreased number of hydrogen bonds between the first monolayer and other inner water shells caused by the very unique hydrogen-bond network patterns in the first ice-like monolayer, which makes it behave like a "hydrophobic water layer." Our findings may have implications for water treatment, non-fouling surfaces, catalysis engine, and biological sensor. © 2013 AIP Publishing LLC.