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

该项目旨在找到一种强大的新途径，在高粘土负载下实现剥离粘土/聚合物纳米复合材料。最近发现的一种自组织过程能够将粘土颗粒在轻轻混合到合适的聚合物中时分解（剥落）成它们各自的薄片（叶子）。这种现象被称为自剥落，因为不需要外部能量输入。在所得的纳米复合材料中，发现粘土叶均匀地分布在整个聚合物基质中（即，随机叶），这对于需要高连接性（机械、电和热）的许多应用是有益的。虽然这种自剥离作为一种新型的纳米复合材料合成方法具有很大的潜力，但由于缺乏对自剥离机制的更好理解，它尚未被应用。计划中的研究的目的是解释自剥离的起源，以便它可以系统地用作在包括石墨烯在内的随机叶子的高负载下创建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纳米复合材料形成的全面表征。不同的实验方法将探讨这一系统的四个相关的长度尺度。将通过流变学研究剥离过程中最相关的宏观体积性质及其机械演化。流变学还将提供剥落动力学的时间尺度，并将以这种方式指导其他实验。将用光学显微镜探测微米尺度，以观察聚集体溶胀以及最终剥离状态的均匀性和随机性。纳米级结构/动力学将用SAXS（小角X射线散射）、USAXS（超SAXS）和SANS（小角中子散射）来观察，以监测粘土廊道间距和锚定到粘土叶的聚合物构象，以及AFM（原子力显微镜）来测试来自拴系的聚合物链的熵拉力的存在。将用NMR（核磁共振）光谱探测原子尺度的键合，以确认氢键的存在并确定氢键是否形成在粘土叶的表面和/或侧面上。研究的初始部分将通过假设两种可能的自剥离机制和对几种不同的自剥离粘土/聚合物系统进行实验来指导。基于这些研究结果，将探索其他自剥离材料组合（石墨烯代替粘土;半结晶聚合物代替无定形聚合物）及其加工条件。两个研究小组的研究结果将相互补充，并导致两个研究小组的研究生和本科生的广泛教育。这包括合作PI在国家同步加速器光源的SAXS/WAXS光束线，这将为本科生/研究生提供一个非常广泛的科学研究视角。

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.