(222aw) Vapor Pressures of Supercooled Liquid Water in No-Man's Land

Since Angell and co-workers [1] reported the rapid variation of thermodynamic properties of supercooled water upon approaching the homogeneous nucleation limit of ice (T_h ~ 231 K), finding the origins to the anomalous properties of supercooled water has been a field of great research interest [2]. One of the competing hypotheses suggests that the anomalous variations near the homogeneous nucleation limit may be due to a second critical point that terminates at the end of a liquid-liquid coexistence region at elevated pressures and more deeply supercooled temperatures [3]. In this scenario, the properties such as the density and the heat capacity should pass through extrema as the liquid passes near this buried critical point.  However, the difficulty of experimentally studying liquid water at deeply supercooled temperatures – in so called no man’s land (T_g ~ 150 K < T < 231 K ~ T_h) [2] – has limited tests of these predictions.   

In this presentation, we discuss a new experimental approach with which to extract information about the liquid state in no man’s land.  We will introduce a method based on the kinetics of heterogeneous freezing from the vapor phase that allows us to extract values for the saturation vapor pressures of both the liquid and solid states at supercooled temperatures.  We will show how these measurements constrain the form of the heat capacity of supercooled liquid water in no man’s land and discuss the implications of these constraints on the hypothetical, buried critical point.  We will also point to extensions of our approach aimed at measurements of structure and dynamics and at understanding the role of specific surface chemistries on the kinetics of freezing.  We will conclude with a discussion of the potential importance of these measurements in the context of high altitude clouds. 

[1] Angell C.A. et al. Journal of Physical Chemistry, 77, 3092 (1973)

[2] Debenedetti P.G. Journal of Physics: Condensed Matter, 15, 1669 (2003)

[3] Poole P.H. et al. Nature, 360, 324 (1992)