| Abstract: | Polyethylene melts normally cannot be crystallized in an isothermally controlled manner below ca. 110°C as crystallization is too fast owing to the presence of preexisting nuclei. We here present a new simple method for producing droplets enabling crystallization to be conducted isothermally down to 75°C and allowing measurements to be performed on them, together with the results of these measurements. We conclude that in contrast to the earlier claims the homogeneous nucleation regime has not been attained even at these low temperatures, the crystal nucleation being dominated by the polymer-substrate interface. The droplets crystallized at these low temperatures have a lamellar morphology as revealed by electron microscopy and grow at rates exceeding 1 m s?1 i.e., six orders of magnitude faster than growth at more usual crystallization temperatures previously considered as “low” (110–120°C)]. We have measured the lamellar thickness l as a function of growth temperature, thus extending the fundamentally important l vs. ΔT (supercooling) relation beyond the previously realizable limits towards high ΔT values. The implications of all these results for the existing ideas of polymer crystallization are likely to be far reaching. Further, the new method for achieving high supercoolings opens up new possibilities for the study of annealing phenomena and the effect of nucleating agents. |
