Effect of Dissolution Temperature

It was found by Kovacs et al. (1966) that at a given temperature the kinetics of crystallization and the size and morphology of the crystals depend on the thermal history of the dilute solutions used and concentration of the polymer (concentrations as low as 0.005 g/ml). In particular, the temperature of dissolution 7 plays a major role, with two types of behavior observed for a typical crystallization temperature 7 of 25 C. (It may be recalled that the temperature of fusion of PEO is 44°C.) 

Enormous differences in the curves may be noted, even for differences in Ts of only a few degrees. If 7 was greater than about 45°C (curve a), an induction period of about 8 hr was observed before crystallization started crystallization then proceeded extremely rapidly, on a log time basis. As long as 45 60 C, excellent reproducibility was found. On the 

The results of this study strongly suggest that dissolution well above the melting temperature of PEO is required to destroy the crystallinity of the lamellae, even in dilute solution. However, dissolution at lower temperatures allows ordered entities to persist these entities can serve as nuclei in subsequent crystallizations. 

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