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Water conduction through the hydrophobic channel of a carbon nanotube
G. Hummer*, J. C. Rasaiah*,†& J. P. Noworyta†
* Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0520, USA
† Department of Chemistry, University of Maine, Orono, Maine 04469, USA
Summary
Matter confinement leads to phase transition at nanoscale. This phenomena is studied in this paper for water where water forms a chain of molecules through carbon nanotube. This chain remains in equilibrium with surrounding water bath. A simulation of 66 ns for single-walled nanotube of length 13.4 A and diameter 8.1A and water run. The nanotube remained filled with 5 water molecules throughout 66 ns. The number of molecules fluctuated between 2 and 7 with 2 only once in 66 ns. The structure and density depletion occured at the nanotube opening. Two of four hydrogen bonds are lost upon entering the nanotube. Only a fraction of the lost energy is recovered by van der Waals interaction with carbon atoms of nanotube. Despite th loss of bonding, weak attraction of water with carbon atoms of nanotube, and very small depth of Lennard-Jones well, the high conduction was surprising but consistent with experimental studies.
The water occupancy was determined from the loss of chemical potential. The binding energies insided nanotube are sharply distributed as compared to bulk phase. Hydrogen bondings inside nanotube are not affected by the changes in the surroundings. During 66 ns, 1,119 water molecules crossed nanotube with 17 water molecules per nanosecond. Water conduction occurs in pulses with peaks of about 30 water molecules per nanosecond. The fluctuation of water molecules transport through carbon nanotube is shown in the following figure.
The chain of water molecules inside nanotube is also shown in the following figure.
Reviewer: Aamir Alaud Din