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

可结晶材料的性能在很大程度上取决于晶体的分数、形态和高阶组织。晶体生长是在成核之前进行的，成核数影响这些参数。控制形核是调整组织形成和材料性能的关键工具。虽然晶体生长和非均相成核已经得到了很好的研究，但对均匀成核的了解要少得多，这主要是由于缺乏分析工具。高熔体过冷时的成核可以用Tammann的两阶段成核方法来研究，该方法适用于慢结晶器，如陶瓷。这种方法意味着在生长可以忽略的低温下形成晶核，在成核缓慢的较高温度下将晶核发展成晶体，从而能够分析其数量并获得精细的多晶结构。对于快速结晶器，应用Tammann的方法还为时过早，需要对其科学基础进行进一步的研究。快速扫描量热仪(FSC)是一种即使在快速结晶器中也可以研究均匀成核的新技术，因为它允许材料受到明确的成核和生长条件的影响。在这个项目中，FSC将与复杂的成像技术一起，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，以确保其对这些系统的适用性，并将挑战核转移-加热率作为一个关键但从未分析过的参数的作用。利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作用力)将产生关于成核过程的结构依赖性的有价值的信息。该项目的结果将促进聚合物和药物加工技术的进一步发展，寻求针对特定应用的定制结构。此外，数据将允许审查成核理论的理论背景，该理论迄今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，将合并马丁·路德大学哈勒-维滕贝格(德国)和喀山联邦大学(俄罗斯)现有的能力，前者专门从事聚合物结晶和具有特定性质的聚合物材料的开发，后者具有有机小分子热力学领域的专门知识。在这两个合作伙伴，都可以使用最先进的FSC和成像工具，提供出色的基础设施。参与单位的不同专业知识将产生协同效应，以加强对晶体成核的了解，以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.