EAGER: Structures of Defects and Interfaces in Block Copolymer Materials

与大量关于硬晶体材料（金属、陶瓷和半导体）缺陷的文献相比，软材料（如聚合物）中缺陷的详细结构受到的关注相对较少，在硬晶体材料中，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缺陷引起的原子的新排列。因此，可以非常详细地了解不同类型的缺陷在控制重要材料性能（如机械强度和导电性）方面的关键作用。本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，用于比较A-B二嵌段共聚物这类重要聚合物材料的微畴界面形态的理论模拟。对于这些材料，A和B畴之间界面面积的最小化与各自域内聚合物分子的拉伸的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镜技术，以探索在技术上重要的双嵌段聚合物材料中经常出现的晶界和线缺陷的3D性质，并可能限制其性能。这项研究也将有助于培养博士后学者和研究生和本科生在先进的电子显微镜和层析成像技术。这个项目的成果也将被纳入相关的研究生课程。本研究旨在对嵌段共聚物（bcp）中网络相、晶界和位错缺陷周围微畴界面的三维形状进行成像。在非晶体bcp中，顺序不是在原子中，而是在分离组件块的界面中（所谓的材料间划分面，IMDS）。以前3D重建的限制将通过使用高角度环形暗场扫描透射电子显微镜（HAADF STEM）的非相干成像来克服。计算工作将定义重建技术的局限性，通过使用理想形态学模型和已知的技术局限性（缺少数据楔，明亮场成像对比度传递函数中的强振荡，倾斜标本的散焦）进行模拟。形态的三维成像至关重要，但非常具有挑战性——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，由于实验限制，可能无法实现可靠的重建。少数文献研究对bcp进行了三维重建，显示了微畴界面的一些看似不现实的特征。如果结果证明这些方法无法克服这些实验限制，那么重点将转向对“可解释分辨率”设置限制，并警告迄今为止发表的文献中的重建可能被“过度解释”。无论结果如何，这些结果对于高分子材料界的观察和理解都是重要的。对于订购的材料，缺陷的存在对材料性能有积极或消极的影响。有了这样的基本理解，应该有可能最终学会操纵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、电池膜等的输运特性，其中聚合物的重量轻、柔韧性和低成本使它们具有很高的吸引力。

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.