Kinetics of nucleation and crystallization in poly
2011-04-02 15:05
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资料摘要:
The recently developed differential fast scanning calorimetry (DFSC) is used for a new look atthe crystal growth of poly(-caprolactone) (PCL) from 185 K, below the glass transition temperature, to 330K,
close to the equilibrium melting temperature. The DFSC allows temperature control of the sample and determination of its heat
capacity using heating rates from 50 to 50,000 K/s. The crystal
nucleation and crystallization halftimes were determined
simultaneously. The obtained halftimes cover a range from 310-2 s (nucleation at 215 K) to 3109 s (crystallization at 185 K). After attempting to analyze the experiments with the classical nucleation and growth model, developed for systems consisting of small molecules, a new methodology is described which addresses the specific problems of crystallization of flexible linear macromolecules. The key problems which are attempted to be
resolved concern the differences between the structures of the various entities identified and their specific role in the mechanism of growth. The structures range from configurations having practicallyunmeasurable latent heats of ordering (nuclei) to being clearly-recognizable, ordered species withrather sharp disordering endotherms in the temperature range from the glass transition to equilibrium melting for increasingly perfect and larger crystals. The mechanisms and kinetics of growth involve also a detailed understanding of the interaction with the surrounding rigid amorphous fraction (RAF) in dependence of crystal size and perfection.
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