Fast water flow through graphene nanocapillaries: a continuum model approach involving the microscopic structure of confined water

TL;DR

This paper develops an analytical continuum model incorporating microscopic water structure to explain the observed enhanced flow of water in graphene nanocapillaries, linking molecular dynamics results with macroscopic flow behavior.

Contribution

It introduces a continuum theory combining disjoining pressure and MD data to elucidate water flow enhancement in hydrophobic nanocapillaries.

Findings

Flow enhancement explained by density and viscosity changes

Model matches experimental flow dependence on nanoconfined water structure

Provides a new framework for nanofluidic flow analysis

Abstract

Water inside a nanocapillary becomes ordered, resulting in unconventional behavior. A profound enhancement of water flow inside nanometer thin capillaries made of graphene has been observed [B. Radha et.al., Nature (London) 538, 222 (2016)]. Here we explain this enhancement as due to the large density and the extraordinary viscosity of water inside the graphene nanocapillaries. Using the Hagen-Poiseuille theory with slippage-boundary condition and incorporating disjoining pressure term in combination with results from molecular dynamics (MD) simulations, we present an analytical theory that elucidates the origin of the enhancement of water flow inside hydrophobic nanocapillaries. Our work reveals a distinctive dependence of water flow in a nanocapillary on the structural properties of nanoconfined water in agreement with experiment, which opens a new avenue in nanofluidics.