Supercooling of liquids

Unlike supercooling of liquids, superheating of crystalline solids is difficult due to nucleation of the liquid at surfaces. However, by suppressing surface melting, superheating to temperatures well above the equilibrium melting temperature has... 

It is perhaps worth while to have a further look at the ice-like clusters which play such an important part in all these theories. In the interests of simplicity they have generally been considered to have a crystalline structure like that of Ice Ih or I but such a requirement is unnecessary and, in view of the supercooling of liquid water which we shall consider presently, unlikely. From the point of view of the cluster theories discussed above, the only requirement on the clusters is that they have substantially tetrahedral bonding and the same sort of molecular volume and vibrational... 

The greater the undercooling, the more rapidly the polymer crystallizes. This is due to the increased probability of nucleation the more supercooled the liquid becomes. Although the data in Fig. 4.8 are not extensive enough to show it, this trend does not continue without limit. As the crystallization temperature is lowered still further, the rate passes through a maximum and then drops off as Tg is approached. This eventual decrease in rate is due to decreasing chain mobility which offsets the nucleation effect. 

There is no generally acceptable comprehensive theory of melting. A feature of the fusion process, which is usually regarded as important in theoretical treatments of the subject, is the inability of a solid to superheat, and only a very small number of exceptions to this generalization are known [2], This almost universal onset of liquefaction immediately upon reaching the melting point is in sharp contrast with the reverse process since supercooling of the vast majority of liquids can be demonstrated under appropriate conditions. 

Heats of fusion, AHfus, are generally expressed in kcal/mol or kJ/mol and entropies of fusion, ASlus in cal/mol-K (e.u. or entropy unit) or J/mol K. The fugacity ratio F, as discussed in Section 1.2.8, is used to calculate the supercooled liquid vapor pressure or solubility for correlation purposes. In the case of liquids such as benzene, it is 1.0. For solids it is a fraction representing the ratio of solid-to-liquid solubility or vapor pressure. 

FIG. 5 The density of liquid and supercooled water as a function of temperature, illustrating the anomalous liquid phase density maximum of water (data from Lide, 2002-2003). 

Several methods are employed to allow the observation of phosphorescence. One of the most common techniques is to supercool solutions to a rigid glass state, usually at the temperature of liquid nitrogen... 

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