EAGER: Structures of Defects and Interfaces in Block Copolymer Materials

非技术概述与有关硬质晶体材料(金属、陶瓷和半导体)缺陷的大量文献相比，聚合物等软材料中缺陷的详细结构受到的关注相对较少，在这些文献中，高分辨率电子显微镜和其他技术已经定量地成像了由各种类型的缺陷引起的原子的新排列，从而使人们能够非常详细地了解不同类型的缺陷在控制诸如机械强度和电导率等重要材料性能方面的关键作用。这项研究将探索使用新的、高度先进的电子显微镜和层析成像技术，试图提供有价值的数据，以便与A-B两嵌段共聚物这类重要聚合物材料的微区界面形态的理论模拟进行比较。对于这些材料，A和B结构域之间的界面面积最小化与相应结构域内聚合物分子的拉伸相互作用控制着界面的形状。此外，PI将扩展和验证先进的显微技术，以探索晶界和线缺陷的3D性质，这些缺陷经常出现在具有重要技术意义的双嵌段聚合物材料中，并可能限制其性能。这项研究还将有助于对博士后学者以及研究生和本科生进行先进的电子显微镜和断层扫描技术的培训。该项目的成果也将纳入相关的研究生课程。技术总结本研究旨在对嵌段共聚物(BCP)中网络相以及晶界和位错缺陷周围的微区界面的3D形状进行成像。在非晶态BCP中，顺序不在原子中，而是在分隔组分块的界面上(所谓的材料间分割面，IMDS)。通过使用高角度环形暗场扫描透射电子显微镜(HAADF STEM)的非相干成像，将克服先前3D重建的限制。计算工作将通过使用理想的形态模型结合已知的技术限制(丢失数据楔形、明场成像的对比度传递函数中的强烈振荡、倾斜样本的散焦)的模拟来定义重建技术的限制。形态的3D成像是至关重要的，但也是非常具有挑战性的--固有的对比度不足和有机材料对电子束损伤的敏感性是巨大的障碍。对于某些形态，由于实验的限制，可能无法实现可靠的重建。少数以BCP的3D重建为特色的文献研究显示了微域界面的一些看似不切实际的特征。如果这些方法最终被证明不能克服这种实验限制，重点将转移到对“可解释的解决方案”设定限制，并警告说，迄今为止出版的文献中的重建可能被“过度解释”了。无论结果如何，这些结果都将是聚合物材料社区查看和了解的重要内容。对于有序材料，缺陷的存在可能会对材料性能产生积极或消极的影响。有了这样的基础知识，最终应该有可能学会操纵BCP系统中的缺陷类型和它们的数量，并相应地影响适用于燃料电池、电池膜等的传输性能，在这些领域，聚合物的重量轻、灵活性和低成本使它们非常有吸引力。

NON-TECHNICAL SUMMARY The detailed structure of defects in soft materials like polymers has received relatively little attention compared to the vast literature on defects in hard crystalline materials (metals, ceramics and semiconductors), where high-resolution electron microscopy and other techniques have quantitatively imaged the new arrangements of the atoms caused by the various kinds of defects, thus enabling a very detailed understanding of the key role of different kinds of defects on controlling important material properties such as mechanical strength and electrical conductivity. This research will explore the use of new, highly advanced electron microscopic and tomographic techniques in an attempt to provide valuable data for comparison to theoretical simulations of the morphology of microdomain interface morphology in important classes of polymeric materials called A-B diblock copolymers. For these materials the interplay of minimization of interfacial area between the A and B domains versus the stretching of the polymer molecules within the respective domains controls the shape of the interface. Additionally, the PI will extend and verify advanced microscopy techniques to explore the 3D nature of grain boundary and line defects that can frequently occur in technologically important diblock polymeric materials and can limit their performance. This research will also contribute to the training of postdoctoral scholars and graduate and undergraduate students in advanced electron microscopic and tomographic techniques. Results from this project will also be incorporated into relevant graduate-level courses. TECHNICAL SUMMARYThis research seeks to image the 3D shape of the microdomain interface in network phases and around grain boundary and dislocation defects in block copolymers (BCPs). In noncrystalline BCPs, the order is not in the atoms but in the interfaces separating the component blocks (the so called Intermaterial Dividing Surface, IMDS). Previous limitations to 3D reconstructions will be overcome via incoherent imaging using high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM). Computational work will define the limitations of the reconstruction techniques by simulations using ideal morphological models combined with the known technique limitations (missing data wedge, strong oscillations in the contrast transfer function for bright-field imaging, defocus across tilted specimens). 3D imaging of the morphology is crucial but very challenging -- the inherent lack of contrast and the susceptibility of organic materials to electron beam damage are formidable obstacles. For some morphologies, reliable reconstructions may not be realizable due to experimental limitations. The few literature studies featuring 3D reconstructions of BCPs display some seemingly unrealistic features of the microdomain interface. Should the approaches turn out to be unable to overcome such experimental limitations, the focus will shift to setting limits on "interpretable resolution" and cautioning that the reconstructions in the published literature to date may have been "overinterpreted". No matter what the outcome, these results will be important for the polymer materials community to view and to understand. For ordered materials, the presence of defects can contribute positively or negatively to material performance. With such fundamental understanding, it should be possible to eventually learn to manipulate the defect types and their numbers in BCP systems and accordingly influence transport properties applicable to fuel cells, battery membranes, etc., where the light weight, flexibility, and low cost of polymers makes them highly attractive.