Supercooled Water. Considerations about the System Organization of Liquid Water

Author(s): Scheiber, E., Resch, G.

Journal/Book: Monatshefte für Chemie. 1989; 120: 671-690.

Abstract: Supercooled water shows increasing values in heat capacity, free energy difference (in relation to ice) and compressibility as the temperature is lowered, whereas the density is decreased. After careful consideration of the boundary conditions, as they are required for the preparation of supercooled water, the reorganizations within the liquid were investigated and the changes in differentiations examined. Different groups of water molecules are distinguished, namely those at the interface, around dissolved gas molecules, around hydrophilic solutes and the vast majority of the remaining water molecules. lt is emphasized that all of these groups are required for the existence of liquid water. Their continuous interrelations are described by the introduction of "hierarchic levels", as they are characteristic for a system organization.The highest hierarchic level is that of the interface, the forces of which regulate and control the exchange of matter and energy both with the environment and within the liquid phase. Subordinated to this level is that of the dissolved gas molecules and their surrounding water molecules. In both of these levels the dynamic aspects are highly developed. Subordinated to this level is that of the hydrophilic solutes and their surrounding water molecules. Their unavoidable presence in liquid water is evidenced by the self-ionization equilibrium. The lowest level is that of all of the other water molecules, which provides some kind of more static boundary conditions for the exercise of the better developed dynamic features of the higher levels.In order to obtain supercooled water, the dynamic features must be improved in the higher hierarchic levels, whereas in the lower levels the more static features should remain as small as possible. The former is achieved by certain cooling modes, by increased surface area, by hydrophobic environment and by increasing gas concentration in the liquid. On the other hand, the concentration of hydrophilic solutes must be minimized (the purity of water enhanced). The metastable state is dynamically better maintained, the better the system organization is developed. The state of supercooled water approaches that of optimal system organization in the temperature range between -20o and - 30 o C.

Keyword(s): Supercooled water

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