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

该项目旨在寻找一条在高粘土含量下制备剥离粘土/聚合物纳米复合材料的有效新途径。最近发现的一种自组织过程是，当粘土颗粒被轻轻混合到合适的聚合物中时，能够将粘土颗粒分解(剥离)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。在得到的纳米复合材料中，发现粘土叶子均匀地分布在聚合物基质中(即随机叶子)，这对于许多需要高连接性(机械、电气和热)的应用是有益的。虽然这种自剥离作为一种新型的纳米复合材料合成工艺具有很大的潜力，但由于缺乏对自剥离机理的更好理解，它还没有被应用。这项计划中的研究旨在解释自剥离的起源，以便系统地利用它作为一种新的途径，在包括石墨烯在内的高随机叶片负载下创建新型聚合物纳米复合材料。PI和co-PI的协同专业知识将使对纳米复合材料形成的充分表征成为可能。不同的实验方法将探索这一系统的四个相关长度尺度。通过流变学研究剥离过程中宏观尺度的块体性质及其力学演化，这在工业上是最相关的。流变学还将提供剥离动力学的时间尺度，并将以这种方式指导其他实验。用光学显微镜对微米尺度进行探测，观察骨料的膨胀和最终剥离状态的均质性和随机性。纳米尺度的结构/动力学将用SAXS(小角X射线散射)、USAXS(超小角中子散射)和SANS(小角中子散射)来观察，以监测粘土走廊间距和锚定在粘土叶子上的聚合物构象，并使用原子力显微镜(AFM)来测试被系系聚合物链是否存在熵拉力。原子级的成键将用核磁共振波谱来探测，以确认氢键的存在，并确定是否在粘土叶子的表面和/或侧面形成氢键。研究的初始部分将通过假设两种可能的自剥离机制以及通过对几种不同的自剥离粘土/聚合物系统的实验来指导。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；半结晶聚合物代替无定形聚合物)及其加工条件。两个研究组的研究成果将相互补充，对两个研究组的研究生和本科生进行广泛的教育。这包括联合PI在国家同步加速器光源的SAXS/WAXS光束线，它将为本科生/研究生提供异常广阔的科学研究视角。

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.