Freezing supercooling effect

Muller-Thurgau 4 states that filter paper moistened with distilled water freezes at —0-1° C., whilst a clay sphere, under similar conditions, has been found to freeze at —0-7° C.3 These observations refer to the actual freezing-points under the conditions named, and are quite apart from supercooling effects, which, as shown above, may be extended to much lower temperatures.6... 

The quality of the mean-field approximation can be tested in simulations of the same lattice model [13]. Ideally, direct free-energy calculations of the liquid and solid phases would allow us to locate the point where the two phases coexist. However, in the present studies we followed a less accurate, but simpler approach we observed the onset of freezing in a simulation where the system was slowly cooled. To diminish the effect of supercooling at the freezing point, we introduced a terraced substrate into the system to act as a crystallization seed [14]. We verified that this seed had little effect on the phase coexistence temperature. For details, see Sect. A.3. At freezing, we have... 

The viscosity of supercooled water is continuous through the freezing point. The effect of temperature on the fluidity of water according to... 

This happened because of our investigation of the rate of nucleation of ice in deeply supercooled water. Previous laboratory studies of the freezing of water occurred in substantially warmer water and were blind to the phase of ice obtained. We studied water undergoing nucleation at roughly the temperature of nucleation in cirrus clouds, I believe. I understand that what happens in cirrus clouds has an important effect on the climate. Moreover, we showed directly that the ice first nucleated was the metastable cubic ice, not the ordinary hexagonal ice. Atmospheric scientists had inferred that result from indirect evidence. Previously it had not been possible to carry out experiments like ours in the laboratory, which is why our work attracted the attention of atmospheric scientists. 

The same apparatus was used to measure the kinetics of emulsion crystallization under shear. McClements and co-workers (20) showed that supercooled liquid n-hexadecane droplets crystallize more rapidly when a population of solid n-hexa-decane droplets are present. They hypothesized that a collision between a solid and liquid droplet could be sufficient to act as a nucleation event in the liquid. The frequency of collisions increases with the intensity of applied shear field, and hence shearing should increase the crystallization rate. A 50 50 mixture of solid and liquid n-hexadecane emulsion droplets was stored at 6 -0.01 °C in a water bath (i.e., between the melting points and freezing points of emulsified n-hexadecane). A constant shear rate (0-200 s ) was applied to the emulsion in the shear cell, and ultrasonic velocities were determined as a function of time. The change in speed of sound was used to calculate the percentage solids in the system (Fig. 7). Surprisingly, there was no clear effect of increased shear rate. This could either be because increase in collision rate was relatively modest for the small particles used (in the order of 30% at the fastest rate) or because the time the interacting droplets remain in proximity is not affected by the applied shear. 

The latter values are approximately five times larger. This shows that the simple dependence of the hydrophobic effect on the number of carbon atoms becomes rather complicated when considering the interfacial properties. These differences thus may be suggestive of the differences in orientation of the aUcyl chains at the interfaces. This subject has been recently investigated by measuring surface tension and interfacial tension near the freezing point of the oil (alkanes) phase under supercooled measurements, as described further below. 

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