284288 Homogeneous Nucleation Temperature of Water in the Doubly Metastable, Supercooled-Superheated State
Homogeneous nucleation temperature of water in the doubly metastable, supercooled-superheated state
Eugene Choi, I-Tzu Chen and Abraham Stroock
The origins of the anomalous behaviors of temperature-dependent thermodynamic parameters of supercooled liquid water are not fully understood . Theoretical  and computational  studies point to the possibility of unusual and fundamental features in the regime of the phase diagram where water is supercooled and stretched (at negative pressure). However, lack of experimental data in this regime limits the depth of investigation. To our knowledge, the only experimental study done in this regime is the measurement of temperature of maximum density down to a pressure of -250 bar, far above the position of the predicted spinodal line .
In this presentation, we will report on our measurements of homogeneous nucleation temperatures of water in the supercooled-superheated regime that is achieved at negative pressures and reduced temperatures. This regime is metastable with respect to both the solid and vapor phases. First, liquid water is trapped in macroscopic spherical voids dispersed in a porous organic hydrogel membrane. The sample is placed in an environmental chamber at a controlled temperature and activity of water vapor. The activity of water vapor is calculated based on the measured saturation pressure of supercooled water at a given temperature. Over time, supercooled water in the voids equilibrates with the sub-saturated water vapor, allowing the macroscopic volumes of liquid water to reach a supercooled-superheated state at well-defined temperatures and chemical potentials . We will present the homogeneous nucleation points (T,P) measured in such a system and compare them with predictions based on extrapolations from nucleation theories and from the previous measurements at positive pressure and temperatures. Finally, we will conclude with a discussion of the relevance of these measurements to the global understanding of water’s thermodynamic properties.
 C.A. Angell, Ann.Rev.Phys.Chem., 34, 593 (1983)
 P.H. Poole et al., Phys.Rev.Lett., 73, 12 (1994)
 I.Brovchenki et al., J.Chem.Phys., 123, 044515 (2005)
 Henderson and Speedy, J.Phys.Chem.,91(11), 3062 (1987)
 T.D. Wheeler and A.D. Stroock, Nature, 455, 208 (2008)