Fast scanning chip calorimetry combined with time resolved X-ray diffraction: a new view on polymer crystallization and melting

In the last decades, different fast scanning calorimetry (FSC) techniques have been developed, able to operate at scanning rates up to 40000 °C/s and higher. To allow for such rates, sub microgram samples are required. Relating calorimetric events to structural changes in minute amounts of material is a major challenge in high speed calorimetry. To be able to characterize materials under FSC conditions, we developed a unique setup, combining FSC with in-situ synchrotron X-ray Diffraction. A study on the melting and crystallization of high-density polyethylene at scanning rates up to 200 °C/s demonstrated the capabilities of the combined approach and revealed relevant FSC instrumental issues that could only be disclosed thanks to the combination of the two techniques. Furthermore, the isothermal crystallization of polyamide 11 at temperatures between vitrification and melting was investigated, aiming at unravelling the origin of the bimodal crystallization rate as a function of supercooling. With our innovative approach we found that the crystallization retardation at intermediate supercooling results from the impeded crystallization when the mesomorphic and crystalline phase form at the same time, a process which we refer to as self-poisoning. In addition, heating traces subsequent to isothermal crystallization show multiple endothermic melting events, which is a signature of melting following recrystallization.status: publishe