Correlation Between Ice-formation Activity Of Substances And The Structure Of Hydrate Shells Of Their Crystals
CORRELATION BETWEEN ICE-FORMATION ACTIVITY OF SUBSTANCES AND THE STRUCTURE OF HYDRATE SHELLS OF THEIR CRYSTALS
A.V. Turov1, V.V. Turov, and A.V. Arkharov 1
Institute of Surface Chemistry of the National Academy of Science,
Pr.Nuki 31, 252022 Kyiv, Ukraine, e-mail vtur@uninet.kiev.ua
1Department of Chemistry, Taras Shevchenko University
Vladimirska St. 60, Kyiv, Ukraine
At present, seeding of ice-nucleation agents (INA) into clouds is considered to be the only applicable method to diminish damage caused by hails, to dissipate clouds and mists over airport areas, and to increase precipitation. The most effective among the above agents is silver iodide. Some organic compounds have a high ice-formation activity (IFA) too. Here belong 1,5-dioxynaphtalene (DON), fluoroglucin (FG), etc. On a process of ice formation caused by loading of dispersed particles of INA into a supercooled liquid, the substance/water phase system undergoes certain transformation leading to formation of the substance/ice one. The important factors influencing the above process relate to some peculiarities in the water layers structurized by the surface at the interface. Therefore, a great interest is focused on studies of boundary water layers at the interface of INA and their
Table 1. Comparison of ice-formation activity and characteristics of layers of adsorbed water on the surface of INA
Compounds
Temperature of ice-formation
Thickness of the adsorbed water layers CH2O (mg/g)
DGS
J/g
AgI
0 (active)
5
0.5
FG
-2 (active)
38
4.9
1,5-DON
-6 (active)
50
3.5
2,6-DON
-12 (non-active)
170
15
2,7-DON
-12 (non-active)
180
19
non-active analogues. We have chosen 1.5-, 2.8-, and 2,7-DON FG and silver iodide (AgI) as the subjects of our study of these DON only 1.5-DON is considered to be active.
Characteristics of adsorbed water layers were determined by 1H NMR method. The main obtained parameters was thickness of adsorbed water layers (CH2O) and free surface energy (DGS).
The data given in table 1 show that the IFA of INA undergoes changes in accordance with the following sequence: AgI>FG>1.5-DON>2.6(2.7)DON. The reverse dependence is observed for the thickness of the adsorbed water film. The free surface energy of studied adsorbents decreases as a function of IFA. Besides, an increase in IFA leads to a corresponding rise in a ratio of intensities between the signal of the broad and narrow components. Thus, the two reasons responsible for high IFA may be distinguished. They are as follows: a low adsorption capacity toward water molecules and the formation of “mobile” ice at the interface.
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