Supercooling effect

Volume measurements needed to calculate the SFI are made by observing and recording the position of the dye solution meniscus in the graduated capillary tube at one temperature (typically 60°C) or two temperatures at which the sample is fully molten, and at desired measurement temperatures (which will be lower than the clear point of the sample). The sample is brought to the first measurement temperature from 0°C after a standardized tempering procedure. This and subsequent measurement temperatures must be approached from below to avoid supercooling effects. Temperature is controlled by immersing the whole dilatometer in constant temperature water baths or an ice-water bath. 

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... 

Umemoto, S., Kobayashi, N., and Okui, N., Molecular weight dependence of crystal growth rate and its degree of supercooling effect, J. Macromol. ScL, Part B Phys. 41, 923-938, 2002. 

This supercooling effect also suggests a kinetic mechanism for chain folding. 

Given that the fractionation mechanism in Crystaf and TREF are very similar, they both provide analogous information about polymer microstructure, with the TREF profiles shifted to higher temperatures due to the supercooling effect in Crystaf, as exemplified in Figure 19. Crystaf analysis times tend to be shorter because of the extra time required by the additional elution step in TREF. 

Crystaf has often been compared to other techniques, specifically Tref and DSC [1,2,54-56]. It is generally accepted that Crystaf and Tref profiles differ mainly by a temperature shift due to the supercooling effect in Crystaf, similar to what is observed between the heating and cooling cycles in DSC. 

Figure 6.3 Differential scanning calorimetry of a commercial Isotactic polypropylene sample, generously provided by Dr. S. J. Han of the Exxon Research and Engineering Company. Note the supercooling effect on crystallization, but the equal and opposite heats of melting and crystallization (13). Experiment by S. D. Kim.

K. Juliet Vogel, 2004, Ph.D Thesis, Rensselaer Polytechnic Institute, Troy, New York, Solute Redistribution and Constitutional Supercooling Effects in... 

Thirdly, the vibration frequency of flie H-O bond for water molecules confined in the plasma-treated silica surfaces is around 3,200 cm (bulk feature) and that confined in the untreated silica is around 3,400 cm (skin feature with higher [17], which indicates that hydrophilic interface produces no surface effect. The air gap between the water and the hydrophobic substrate [16] makes the contacting skin more like free. However, water confined in hydrophilic nanopores [50, 51] or wetting with hydrophilic topologic configurations [52] exhibits supercooling effect, or melts at lower temperature than usual because of the lacking of broken bonds. 

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