Water conduction through the hydrophobic channel of a carbon nanotube

Abstract

Confinement of matter on the nanometre scale can induce phase transitions not seen in bulk systems. In the case of water, so-called drying transitions occur on this scale as a result of strong hydrogen-bonding between water molecules, which can cause the liquid to recede from nonpolar surfaces to form a vapour layer separating the bulk phase from the surface. Here we report molecular dynamics simulations showing spontaneous and continuous filling of a nonpolar carbon nanotube with a one-dimensionally ordered chain of water molecules. Although the molecules forming the chain are in chemical and thermal equilibrium with the surrounding bath, we observe pulse-like transmission of water through the nanotube. These transmission bursts result from the tight hydrogen-bonding network inside the tube, which ensures that density fluctuations in the surrounding bath lead to concerted and rapid motion along the tube axis. We also find that a minute reduction in the attraction between the tube wall and water dramatically affects pore hydration, leading to sharp, two-state transitions between empty and filled states on a nanosecond timescale. These observations suggest that carbon nanotubes, with their rigid nonpolar structures, might be exploited as unique molecular channels for water and protons, with the channel occupancy and conductivity tunable by changes in the local channel polarity and solvent conditions.

Self-assembling subnanometer pores with unusual mass-transport properties

“…We noted recent studies on carbon nanotubes showing that water can spontaneously fill small hydrophobic nanopores 36,37 , especially those with small pore diameters [36][37][38][39][40][41][42] , leading to enhanced mass flow or resonance 40,43 . The observed ion conductance of the hydrophobic channel formed by 1a implies that this sub-nm pore may also be filled with water molecules.…”

Empirical Nanotube Model for Biological Applications

“…Define V i as the quantum chemistry ESP at grid point i, and V̂i as the one calculated from RESP charges. The RRMSD is given by 26 (1) Another figure of merit of the RESP scheme is the lowest non-zero multipole moment. Since the SWNT segments in our study are charge neutral and non-polar, net charge and dipole moments vanish.…”

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

“…This comes about because of the greater corrugation of the energy landscape on boron nitride arising from specific electronic structure effects. We discuss how a subtle dependence of the friction on the atomistic details of a surface, that is not related to its wetting properties, may have a significant impact on the transport of water at the nanoscale, with implications for the development of membranes for desalination and for osmotic power harvesting.Nanofluidics is an exciting field that offers alternative and sustainable solutions to problems relating to energy conversion, water filtration and desalination [1][2][3][4][5][6][7][8][9]. Miniaturization towards nanofluidic devices inevitably leads to an enhanced influence of surface and interface properties as opposed to those of the bulk.…”