La Rivista del Nuovo Cimento

Year 2011 - Issue 5 - May

Transport properties of supercooled confined water

Authors: F. Mallamace, P. Baglioni, C. Corsaro, J. Spooren, H. E. Stanley, S.-H. Chen
DOI: 10.1393/ncr/i2011-10065-4
pp. 253-388
Published online 7 June 2011
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Abstract: We present an overview of recent experiments performed on water in the deeply supercooled region, a temperature region of fundamental importance in the science of water. We examine data generated by nuclear magnetic resonance, quasi-elastic neutron scattering, Fourier-transform infrared spectroscopy, and Raman spectroscopy, and study water confined in nanometer-scale environments. When contained within small pores, water does not crystallize and can be supercooled well below its homogeneous nucleation temperature $T_{H}$. On this basis, it is possible to carry out a careful analysis of the well-known thermodynamic anomalies of water. Studying the temperature and pressure dependencies of water dynamics, we show that the liquid-liquid phase transition (LLPT) hypothesis represents a reliable model for describing liquid water. In this model, liquid water is a mixture of two different local structures: a low density liquid (LDL) and a high-density liquid (HDL). The LLPT line terminates at a low-T liquid-liquid critical point. We discuss the following experimental findings: i) the crossover from non-Arrhenius behavior at high T to Arrhenius behavior at low T in transport parameters; ii) the breakdown of the Stokes-Einstein relation; iii) the existence of a Widom line, which is the locus of points corresponding to a maximum correlation length in the P-T phase diagram and which ends in the liquid-liquid critical point; iv) the direct observation of the LDL phase; and v) the minimum in the density at approximately 70K below the temperature of the density maximum. In our opinion these results strongly support the LLPT hypothesis. All of the basic science and technology community should be impressed by the fact that, although the few ideas (apparently elementary) developed concerning water approximately 27 centuries ago have changed very little up to now, because of the current expansion in our knowledge in this area, they can begin to change in the near future.