Phase diagram of water in carbon nanotubes
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Edited by Benjamin Widom, Cornell University, Ithaca, NY, and approved November 12, 2007 (received for review August 22, 2007)
Abstract
A phase diagram of water in single-walled carbon nanotubes at atmospheric pressure is proposed, which summarizes ice structures and their melting points as a function of the tube diameter up to 1.7 nm. The investigation is based on extensive molecular dynamics simulations over numerous thermodynamic states on the temperature–diameter plane. Spontaneous freezing of water in the simulations and the analysis of ice structures at 0 K suggest that there exist at least nine ice phases in the cylindrical space, including those reported by x-ray diffraction studies and those unreported by simulation or experiment. Each ice has a structure that maximizes the number of hydrogen bonds under the cylindrical confinement. The results show that the melting curve has many local maxima, each corresponding to the highest melting point for each ice form. The global maximum in the melting curve is located at ≈11 Å, where water freezes in a square ice nanotube.
Footnotes
- *To whom correspondence should be addressed. E-mail: koga{at}cc.okayama-u.ac.jp
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Author contributions: D.T., I.H., K.K., and H.T. performed research and K.K. wrote the paper.
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The authors declare no conflict of interest.
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This article is a PNAS Direct Submission.
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Freely available online through the PNAS open access option.
- © 2007 by The National Academy of Sciences of the USA
