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

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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.