Complex Behavior of Ordered and Icelike Water in Carbon Nanotubes near Its Bulk Boiling Point

We report the results of extensive molecular dynamics (MD) simulation of water in a carbon nanotube (CNT) with a specific diameter over a wide range of temperatures from 343 to 423 K. In order to characterize the nature of water, we have computed the Kirkwood g-factor, the ten Wolde parameter, the radial distribution, the cage correlation, the intermediate scattering functions, the mean-square displacements of the water molecules, and the connectivity of the oxygen atoms. The computed properties provide evidence for complex behavior. Some of the properties indicate an icelike structure, while others point to ordered (but not necessarily frozen) water. The connectivity is close to 9. The ordered water exists both below and above its bulk boiling point. The order is identified based on the ten Wolde parameter and may explain, along with the dynamic slow down, the recent discovery of "ice" in CNTs near the bulk boiling point in a certain range of CNT diameters, not seen in tubes of other sizes.