EAGER: Structures of Defects and Interfaces in Block Copolymer Materials

非技术性总结 与大量的关于硬晶体材料缺陷的文献相比，软材料如聚合物中缺陷的详细结构受到的关注相对较少（金属、陶瓷和半导体），其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，从而使得能够非常详细地理解不同种类的缺陷在控制重要的材料性能（例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断层扫描技术，试图提供有价值的数据比较的微区界面形态的重要类别的聚合物材料称为A-B二嵌段共聚物的形态的理论模拟。 对于这些材料，A域和B域之间的界面面积的最小化与各自域内的聚合物分子的拉伸的相互作用控制界面的形状。 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二嵌段聚合物材料中经常发生的晶界和线缺陷的3D性质，并限制其性能。 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断层摄影技术。 该项目的成果也将纳入相关的研究生课程。技术概述本研究旨在对嵌段共聚物（BCP）中网络相和晶界周围的微区界面和位错缺陷的3D形状进行成像。在非结晶BCP中，有序性不是在原子中，而是在分隔组分块的界面中（所谓的材料间分隔表面，IMDS）。以前的限制，三维重建将克服通过非相干成像使用高角度环形暗场扫描透射电子显微镜（HAADF STEM）。 计算工作将通过使用理想形态模型结合已知技术限制（缺失数据楔形、亮场成像对比度传递函数的强烈振荡、倾斜标本的散焦）的模拟来定义重建技术的限制。 形态的3D成像至关重要，但非常具有挑战性-有机材料固有的对比度缺乏和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。 少数文献研究具有三维重建的BCP显示一些看似不切实际的功能的微区接口。如果这些方法被证明无法克服这些实验限制，重点将转移到对“可解释分辨率”设置限制，并警告迄今为止已发表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来说都是重要的。对于有序材料，缺陷的存在可以对材料性能产生积极或消极的影响。有了这样的基本理解，应该有可能最终学会操纵BCP系统中的缺陷类型及其数量，并相应地影响适用于燃料电池、电池膜等的传输特性，其中聚合物的轻重量、柔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.