Supercooling definition

A distinction between a solid and liquid is often made in terms of the presence of a crystalline or noncrystalline state. Crystals have definite lines of cleavage and an orderly geometric structure. Thus, diamond is crystalline and solid, while glass is not. The hardness of the substance does not determine the physical state. Soft crystals such as sodium metal, naphthalene, and ice are solid while supercooled glycerine or supercooled quartz are not crystalline and are better considered to be supercooled liquids. Intermediate between the solid and liquid are liquid crystals, which have orderly structures in one or two dimensions,4 but not all three. These demonstrate that science is never as simple as we try to make it through our classification schemes. We will see that thermodynamics handles such exceptions with ease. 

Secondly, fractionation effects have been studied [126] where now the components are the various molecular weights in the solution. They conclude that fractionation will be important even at high molecular weights due to the variation in supercooling of the different molecular weights, and hence their different growth rates. Notice that this result could well be affected by the definition of supercooling as described in Sect. 2.3. 

Liquid solvents in this picture may be considered as islands in the northern hemisphere, because the state of molecules in a liquid solvent is quite definitely closer to the COSMO state than to the vacuum. The only exception may be alkane solvents, which are located somewhere close to the equator due to their fully nonpolar character. Solids may be considered as sunken islands and their depths below sea level may be considered as AG s. As discussed before, the methods to explore this depth are rather limited, but we can be quite sure that in general the depth below sea level will be much smaller than the distance of the islands from the North Pole or from each other. We now explore the methods to go from the sea level position of any island to the North Pole or vice versa. Given such a method we will be able to transfer a compound from any liquid or supercooled liquid state to any other such state. 

The dodecahydrate is efflorescent at room temperature in air. At 22° C. it becomes damp and the dampness increases as the temperature rises until finally the salt becomes completely liquid. A definite melting point is not exhibited.3 The liquid becomes clear at 56 2° C. and is then a true solution of the heptahydrate. When this is supercooled to about 40° C. and seeded with a crystal of the salt, crystals of the heptahydrate are deposited and the temperature rises to 56-2° C. A similar evolution of heat, but less marked, occurs at 22° C. The heptahydrate does not effloresce appreciably at room temperature in air. 

Covacs6 proposed another definition of the fractional free-volume. As the extrapolated volume of supercooled liquids reaches the crystalline state, vc, at temperature rc > 0 K, it is possible to compare this critical temperature with rg , the limit glass temperature at infinitely slow cooling. Free-volume in the crystalline state is assumed to be zero. In this case the value /g according to Doolittle may be compared with /g, c, which characterizes the excess free-volume of glass as compared with the crystalline state ... 

Both spin-crossover transitions (HS < LS, FO LS) are first order accompanied by definite jumps of populations, while the cooperative Jahn-Teller transition (HS FO) is weak first-order (very close to a second-order transition). It suggests a possibility of observation of hidden cooperative Jahn-Teller transition (the broken line in Fig. 7) between the metastable HS and FO phases, if the HS phase could be supercooled enough below the spin-crossover transition temperature Tc by a rapid cooling. 

Note that the magnitude of Fj/2 lies between zero and unity. The quantity Fj/2 is a measure of the fragility of the supercooled liquid. The Fj/2 fragility metric has two notable virtues (1) it is independent of the fitting function employed to analyze the experimental data [37,43] and (2), because of the definition of the midway temperature, the relaxation time at this characteristic temperature is accurately accessible by various experimental techniques [37,43],... 

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