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Published online 23 June 2009 | Nature | doi:10.1038/news.2009.592
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Elusive forms of water found?
Two long sought-after phases of ultra-cold water may have been trapped between crystals of ice.
Researchers in India and Italy say they have seen two types of liquid water that have long been suspected to exist below water's normal freezing point.
Water is undoubtedly a strange liquid.
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The idea of coexisting liquid phases and associated low-temperature critical point in water is the most recent version of the so-called mixture models. It is an outcome of using an ad hoc potential function in computer simulation. The ESR study using probe diffusion, although careful, is a study of inter-granular water whose structure has been seriously altered both by the freeze-concentration of impurities and by confinement to nano-size pockets and veins of polycrystalline ice [1]. Since tetrahedral pockets of water in polycrystalline ice have a higher cross section than the triangular cross section veins of water in it, the two relaxation times obtained may well refer to the two different nano-volume confinements of impure water. It has been well-established that under confinement both structure and dynamics of water are drastically modified [2]. It needs to be stressed that, not only the existence of water of two different densities has been excluded by the available experimental data [3]; it is self-contradictory with the existence of a critical point at lower temperature and pressure. It seems fair to remind us that alternative (and simpler) ways exist to explain the so-called “water anomalies� which essentially discriminate between the dynamics of the molecule from the dynamics of the bonds and identify the temperature of apparent divergence of thermodynamic properties with the homogeneous nucleation temperature [4]. [1] G.P. Johari, W. Pascheto and S.J. Jones, J. Chem. Phys. 100, 4548 (1994). [2] J. Dore, Chem. Phys. 258, 327 (2000); J.M. Zanotti, M.-C. Bellissent-Funel and S.-H. Chen, Europhys. Lett. 71, 91 (2005). [3] R.W. Hendricks, P.G. Mardon and L.B. Schaffer, J. Chem. Phys. 61, 319 (1974); L. Bosio, J. Teixeira and H.E. Stanley, Phys. Rev. Lett. 46, 597 (1981). [4] J. Teixeira, A. Luzar and S. Longeville, J. Phys.: Cond. Matter 18, S2353-S2362 (2006). José Teixeira Lab. Léon Brillouin (CEA/CNRS) CEA Saclay 91191 Gif-sur-Yvette Cedex France