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

可结晶材料的性质在很大程度上取决于晶体的分数、形态和高阶组织。晶体生长在成核之前，核数影响这些参数。控制成核是调整结构形成和材料性能的关键工具。虽然晶体生长和非均相成核得到了很好的研究，但由于缺乏分析工具，对均相成核的了解甚少。高熔体过冷状态下的成核可以采用Tammann的两阶段核发育方法进行研究，该方法在慢结晶剂（如陶瓷）中已得到证实。这种方法意味着在生长可以忽略不计的低温下形成原子核，而在成核缓慢的高温下原子核发育成晶体，从而可以分析它们的数量并获得精细的多晶结构。对于快速结晶器，Tammann方法的应用还不成熟，需要进一步的研究以建立科学的基础。快速扫描量热法（FSC）是一种在快速结晶器中研究均匀成核的新技术，因为它可以使材料具有明确的成核和生长条件。在这个项目中，FSC将与复杂的成像技术一起应用于深入分析由大小有机分子组成的系统中的均相成核，包括聚合物和药物。将进一步发展核发展方法，以确保其适用于这些系统，核转移加热速率作为一个关键但从未分析过的参数的作用将受到挑战。使用具有不同结构特征的大分子和小分子（从而表现出不同的分子间力）将产生有关成核过程结构依赖性的有价值的信息。该项目的成果将促进聚合物和药物加工技术的进一步发展，为特定应用追求量身定制的结构。此外，数据将允许审查成核理论的理论背景，到目前为止，该理论没有区分由不同建筑单元组成的系统。为了实现该项目的目标，专门从事聚合物结晶和具有特定性能的聚合物材料开发的马丁·路德大学（德国）和拥有小有机分子热力学领域专业知识的喀山联邦大学（俄罗斯）的现有能力将相结合。在这两个合作伙伴，最先进的FSC和成像工具，提供了良好的基础设施。参与单位的不同专业知识将产生协同效应，以增强对晶体成核的理解，从而进一步发展材料的化学结构，加工路线和最终性能之间的关系。

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.