Length-dependent water permeation through a graphene channel

Abstract

Water confined in two-dimensional channels exhibits unique properties, such as rich morphology, specific phase transition and a low dielectric constant. In this work, molecular dynamics simulations have been used to study the water transport in two-dimensional graphene channels. The structures and dynamics of water under confinement show strong dependence on the channel length and thickness of the channels. In particular, there exists a critical channel length beyond which monolayer water forms square-like ice structures, leading to the rapid decrease in water flow that eventually ceases completely. The water flow for double-layer and three-layer systems exhibits a similar exponential decay but does not reach zero. The translocation time exhibits an excellent power-law behavior with an increase in the channel length, accounting for the exponential flow decay. The radial distribution function confirms the length-dependent liquid-to-ice phase transition of monolayer water and the liquid states for double-layer and three-layer systems. The formation of monolayer ice can be further supported by the increasing barriers in the potential of mean force and specific dipole distributions. Furthermore, the melting temperature of monolayer ice increases significantly with the increase in the channel length that can also be close to or even exceeds the boiling point at atmospheric pressure. These findings provide new physical insights into the extraordinary length-dependent water behaviors and suggest future experimental studies on high-temperature ice through the size control in nanochannels.