Molecular Origin of Fast Water Transport in Carbon Nanotube Membranes: Superlubricity versus Curvature Dependent Friction

Abstract

In this paper, we study the interfacial friction of water at graphitic interfaces with various topologies, water between planar graphene sheets, inside and outside carbon nanotubes, with the goal to disentangle confinement and curvature effects on friction. We show that the friction coefficient exhibits a strong curvature dependence; while friction is independent of confinement for the graphene slab, it decreases with carbon nanotube radius for water inside, but increases for water outside. As a paradigm the friction coefficient is found to vanish below a threshold diameter for armchair nanotubes. Using a statistical description of the interfacial friction, we highlight here a structural origin of this curvature dependence, mainly associated with a curvature-induced incommensurability between the water and carbon structures. These results support the recent experiments reporting fast transport of water in nanometric carbon nanotube membranes.

Hybrid molecular-continuum simulations of water flow through carbon nanotube membranes of realistic thickness

“…The high permeability arises from the smooth internal structure of nanotubes, producing low-friction fluid transport. Substantial reductions in water-surface friction have been demonstrated with decreasing tube radius (<10 nm) (Falk et al 2010), which explains the many orders of magnitude flow enhancement over continuum fluid theory that is observed in both experiment (Holt et al 2006;Majumder et al 2005;Majumder and Corry 2011) and simulation (Thomas and McGaughey 2009;Kannam et al 2012;Walther et al 2013;Ritos et al 2014).…”

Water flow in carbon nanotubes: The effect of tube flexibility and thermostat

“…The system, or at least a part of it, thus needs to be coupled to a virtual heat bath with large heat capacity. While it would in many cases be most natural to remove the excess heat via the channel walls, the motion of wall atoms is suppressed in the majority of confinedfluid simulations, while applying a thermostat to the fluid [4][5][6][7][8][9][10][11][12][13] or to a subset thereof. 14,15 This simplification is motivated by a considerably lower computational cost since computing a) sarith@iitm.ac.in the wall-wall interactions is not needed when the wall is kept rigid.…”

Friction of Water on Graphene and Hexagonal Boron Nitride from Ab Initio Methods: Very Different Slippage Despite Very Similar Interface Structures

“…For instance, carbon nanotubes have a very high water permeability as compared to the prediction of macroscopic fluid dynamics [2]. Further, a vanishing friction has been found, giving rise to superlubric behavior of water chains inside tubes of sub-nanometre radii [11].Besides carbon, boron nitride (BN) nanostructures have recently been explored for the development of nanofluidic devices for fast water transport and efficient power generation [1,12,13]. Recent interest has been fueled by the demonstration that salinity concentration gradients across BN nanotube membranes can leed to the generation of very large electric currents [1].…”