Four kinds of 1D ice modelled

WORKING WITH large-scale computer simulations, a team of scientists that included Xiao Cheng Zeng, professor of chemistry at the University of Nebraska-Lincoln, has modelled four new kinds of crystalline ice.

They have adjusted the diameter of a carbon nanotube by less than one-quarter of a nanometer (a nanometre is one-billionth of a meter).

A carbon nanotube can be viewed as a graphite sheet that has been rolled up to create a tube that can be as small as one-half a nanometer in diameter, Zeng said.

Zeng and his team, which included three other scientists, Kenichiro Koga of the Fukuoka University of Education in Japan, G.T. Gao of the U.S. Naval Academy and Hideki Tanaka of Okayama University in Japan, studied the formation of quasi-one- dimensional ice crystals in carbon nanotubes in the range of 1.0 to 1.4 nanometres in diameter.

In results published in Nature, they found that ice crystals formed a square structure in a 1.108-nanometer tube.

As they increased the size of the tube's diameter, they found structural changes in the ice crystals at roughly .07-nanometer intervals to pentagonal, hexagonal and heptagonal crystals.

Zeng said ice crystals in the tubes are``quasi-one- dimensional''because they are almost but not quite mathematically one-dimensional ( that is, a line with no width).

``If our study is confirmed experimentally, it would extend the crystalline ice family,''Zeng said.``Right now, there are 13 types of (three-dimensional) ice that have been discovered in nature.

We earlier reported the two-dimensional 'Nebraska' ice and this time we found four members in one-D.

They all satisfy the `ice rule' that every water molecule (except on the surface) forms four hydrogen bonds with its nearest neighbour water molecules.''

If confirmed, Zeng said the discovery could contribute to the study of molecular biological science. `It is known that water provides the 'glue' for the binding of protein molecules via the hydrophobic (water-repellent) attraction force, `he said. `

`Our study of water in hydrophobic micropores is of fundamental importance to this because it will help us to gain deeper insights into the interactions between proteins.''

Zeng said his team's investigation also indicated some new knowledge in the area of physics.

In phase transitions from ice to liquid to vapour or vice versa in the 13 known types of three-dimensional water, scientists have never found a point beyond which there is no difference in structure between the liquid and solid states.

He said there might be such a point at the one-dimensional level. ``We found some evidence from our simulation that maybe in quasi- one-D that beyond critical point, there is no difference between liquid and solid,' he said.

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