Kinetics of crystal nucleation of polymers and low-molecular-weight organic compounds: Using Tammann’s approach to discover differences and similarities

点击翻译按钮获取中文摘要

The properties of crystallizable materials greatly depend on the fraction, morphology, and higher-order organization of crystals. Crystal growth is preceded by nucleation, with the nuclei number affecting these parameters. Controlling nucleation is a key tool to tailor structure formation and material performance. While crystal growth and heterogeneous nucleation are well studied, homogeneous nucleation is understood much less, mainly due to lack of analysis tools.Nucleation at high melt-supercooling can be studied employing Tammann’s two-stage nuclei development method, well-established for slow crystallizers, e.g. ceramics. This approach implies nuclei formation at low temperature where growth is negligible, and development of the nuclei into crystals at higher temperature where nucleation is slow, allowing analysis of their number and obtaining fine polycrystalline structures. For fast crystallizers application of Tammann’s method still is premature, requiring further research for its science-based establishment.Fast scanning calorimetry (FSC) is a new technique to study homogeneous nucleation even in fast crystallizers as it allows subjecting materials to well-defined nucleation and growth conditions. In this project, FSC —together with sophisticated imaging techniques— will be applied for in-depth analysis of homogeneous nucleation in systems composed of large and small organic molecules, including polymers and pharmaceuticals. The nuclei development approach will be further developed to ensure its applicability to these systems and the role of the nuclei-transfer-heating rate as a critical but never before analyzed parameter will be challenged. The employment of large and small molecules with distinct structural features (thus exhibiting different intermolecular forces) will yield valuable information about structure dependence of the nucleation process.The results of the project will promote further development of polymer and pharmaceutical processing technologies, pursuing tailored structures for specific applications. In addition, data will allow reviewing the theoretical background of the nucleation theory, which, so far, does not distinguish between systems composed of different building units.To achieve the goals of the project, capacities available at the Martin Luther University Halle-Wittenberg (Germany), specialized in polymer crystallization and development of polymeric materials with specific properties, and Kazan Federal University (Russia), with expertise in the field of thermodynamics of small organic molecules, will be combined. At both partners, state-of-the-art FSC and imaging tools are available, providing an excellent infrastructure. The different expertise of the participating units will yield synergetic effects towards an enhanced understanding of crystal nucleation to further develop relations between the chemical structure of a material, processing routes, and final properties.