Phase transitions in confined water nanofilms

Bulk water has three phases: solid, liquid and vapour. In addition to undergoing a phase transition (of the first order) between them, liquid and vapour can deform continuously into each other without crossing a transition line-in other words, there is no intrinsic distinction between the two phases. Hence, the first-order line of the liquid-vapour phase transition should terminate at a critical point. In contrast, the firstorder transition line between solid and liquid is believed to persist indefinitely without terminating at a critical point1. In recent years, however, it was reported that inside carbon nanotubes, freezing of water may occur continuously as well as discontinuously through a first-order phase transition2. Here we present simulation results for water in a quasi-twodimensional hydrophobic nanopore slit, which are consistent with the idea that water may freeze by means of both firstorder and continuous phase transitions. Our results lead us to hypothesize the existence of a connection point at which first-order and continuous transition lines meet3,4. © 2010 Macmillan Publishers Limited. All rights reserved.