Research Highlights

Nature Nanotechnology Published online: 5 January 2007 | doi:10.1038/nnano.2007.3

Subject Categories: Carbon nanotubes and fullerenes | Computational nanotechnology

Nanostructures: On thin ice

Stuart Cantrill

Computer modelling reveals that water molecules confined inside carbon nanotubes freeze under high pressure to form helical ice sculptures

NanostructuresOn thin ice

2006 National Academy of Sciences USA

Although relatively small and quite simple in terms of their composition, water molecules crystallize into a diverse range of ordered structures in the solid state. Ice crystals are held together by strong intermolecular interactions, known as hydrogen bonds, between the hydrogen and oxygen atoms of adjacent molecules.

When water freezes in a confined space — such as inside a carbon nanotube — structures very different to those observed in the bulk are formed. Now, Xiao Zeng and co-workers1 from the University of Nebraska in the USA have studied the effects of pressure on this process. A series of simulations were performed in which water molecules were located inside a nanotube and pressure was applied at each end as the temperature was lowered. In each case, helical arrangements of water molecules were observed, with the precise structure depending on the diameter of the nanotube in question and the magnitude of the applied pressure. Double-walled assemblies were observed in smaller tubes, whereas triple-walled structures formed inside the larger ones.

This study allows the fluid properties and phase transitions of one of the most well known substances to be investigated at the nanoscale. Moreover, it demonstrates that the beauty of ice crystals does not depend on scale — the structures unveiled in this study are as pretty as any snowflake.



  1. Bai, J., Wang, J. & Zeng, X. C. Multiwalled ice helixes and ice nanotubes. Proc. Natl Acad. Sci. USA 103, 19664–19667 (2006). | Article |

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