Collaborative Research: Self-Exfoliation as Promising Route to Novel Nanocomposite Processing

该项目旨在寻找一种强大的新途径，以实现高粘土负载下的剥落粘土/聚合物纳米复合材料。最近发现的一种自组织过程是，当将粘土颗粒轻轻混合到合适的聚合物中时，它能够将粘土颗粒分解（剥离）成单独的薄片（叶子）。这种现象被称为自我剥离，因为不需要外部能量输入。在得到的纳米复合材料中，粘土叶被发现均匀分布在聚合物基体中（即随机叶），这对于许多需要高连通性的应用（机械、电气和热）是有益的。虽然这种自剥离作为一种新的纳米复合材料合成工艺具有很大的潜力，但由于缺乏对自剥离机制的更好理解，它尚未得到应用。计划研究的目的是解释自剥离的起源，以便系统地利用它作为在包括石墨烯在内的随机叶片的高负载下制造新型聚合物纳米复合材料的新途径。PI和co-PI的协同专业知识将允许对纳米复合材料地层进行全面表征。不同的实验方法将探索该系统的四个相关长度尺度。在工业上最相关的剥落过程中，宏观体积特性及其力学演化将通过流变学进行研究。流变学还将提供剥落动力学的时间尺度，并以这种方式指导其他实验。光学显微镜将在微米尺度上进行探测，观察聚集体的膨胀以及最终剥离状态的均匀性和随机性。纳米级结构/动力学将通过SAXS（小角度x射线散射）、USAXS（超SAXS）和SANS（小角度中子散射）来观察粘土通道间距和固定在粘土叶片上的聚合物构象，以及AFM（原子力显微镜）来测试拴在粘土链上的熵拉力的存在。原子尺度上的键合将用核磁共振（NMR）波谱来探测，以确认氢键的存在，并确定氢键是否在粘土叶的表面和/或侧面形成。研究的最初部分将通过假设两种可能的自剥离机制，以及对几种不同的自剥离粘土/聚合物系统进行后续实验来指导。在这些研究成果的基础上，将探索其他自剥离材料组合（石墨烯代替粘土；半结晶聚合物代替非晶态聚合物）及其加工条件。两个研究小组的研究成果将相互促进，并为两个研究小组的研究生和本科生提供广泛的教育。这包括联合pi在国家同步加速器光源的SAXS/WAXS光束线，这将为本科生/研究生提供科学研究的异常广阔的视角。

The project aims to find a powerful new route towards exfoliated clay/polymer nanocomposites at high clay loading. A recently discovered self-organizing process is able to disintegrate (exfoliate) clay particles into their individual thin sheets (leaves) when being gently mixed into a suitable polymer. The phenomenon is called self-exfoliation, since no external energy input is required. In the resulting nanocomposite, the clay leaves were found to distribute uniformly throughout the polymer matrix (i.e., random leaves), which can be beneficial for many applications that require high connectivity (mechanical, electrical, and thermal). While such self-exfoliation has great potential as a novel nanocomposite synthesis process, it has not yet been applied due to the lack of a better understanding of the self-exfoliation mechanism. The planned research has the objective of explaining the origins of the self-exfoliation so that it can be utilized systematically as a new path for creating novel polymer nanocomposites at high loadings of random leaves including graphene. The synergistic expertise of the PI and co-PI will allow a full characterization of the nanocomposite formation. Diverse experimental methods will probe the four relevant length scales of this system. The macro-scale bulk properties and their mechanical evolution during exfoliation, which are most relevant industrially, will be studied through rheology. Rheology will also provide the time scales of the exfoliation dynamics and will guide the other experiments in this way. The micron-scale will be probed with optical microscopy to observe aggregate swelling and the homogeneity and randomness of the final exfoliated state. The nano-scale structure/dynamics will be observed with SAXS (small angle x-ray scattering), USAXS (ultra-SAXS), and SANS (small angle neutron scattering) to monitor clay gallery spacing and a polymer conformation anchored to a clay leaf, and AFM (atomic force microscopy) to test for the presence of an entropic-pulling force from the tethered polymer chains. The bonding at the atomic scale will be probed with NMR (nuclear magnetic resonance) spectroscopy to confirm the presence of hydrogen bonds and determine if hydrogen bonds form on the face and/or sides of a clay leaf. The initial part of the research will be guided by hypothesizing two possible self-exfoliation mechanisms and by following up with experiments on several different self-exfoliating clay/polymer systems. Based on these research findings, other self-exfoliating material combinations (graphene instead of clay; semicrystalline polymers instead of amorphous polymers) and their processing conditions will be explored. Research results from the two research groups will feed into each other and lead to a broad education of graduate and undergraduate students of the two research groups. This includes the co-PI's SAXS/WAXS beamline at the National Synchrotron Light Source, which will provide undergraduate/graduate students with an unusually broad perspective on scientific research.