Controlling Microstructure of Hybrid Thin Films through Flow-Induced Orientation

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Composite materials are designed and processed to take synergistic advantage of the combined properties of the two component materials. Biomineralization, the process by which living organisms produce minerals, typically results in a composite system where the mineral forms the structural frame while an organic component assumes the biological function. Nacre, a shell material also known as mother of pearl, is a representative example, being composed of a large fraction of inorganic calcium carbonate (hard and brittle) and a small fraction of protein (soft and tough). Their combination in a layered structure leads to the outstanding mechanical properties in contrast to the individual components. Such carefully organized composites have inspired scientists to synthesize materials with a similar structure at a large scale for practical applications, but their efforts have not yet proven successful. The basic challenge is the difficulty of incorporating a large concentration of inorganic nanomaterials into a polymer system, and simultaneously achieving a high level of organization. This award supports fundamental research to explore a facile approach to prepare hybrid materials with a nacre-like microstructure and to achieve similar outstanding mechanical properties and other important functionalities. By taking advantage of flow-induced orientation of disc-like particles, the manufacturing of materials at a high rate appears to be possible. The composite films prepared through this approach should find application in packaging with improved barrier properties and corrosion resistance. Fully integrated within this project are activities to increase the interest in science and technology among the younger generation, particularly those in underrepresented groups.This research will lead to a thorough understanding of the fundamental mechanisms for the flow induced orientation and stacking of platelets that can help lead to optimal alignment of these particles in composite films to mimic the nacre structure. Factors such as flow rate, system viscosity, nanosheet concentration and aspect ratio, and related chemistry will be systematically investigated to address two fundamental questions. First, how do these factors affect the alignment and packing of nanosheets? Secondly, how will the interface between the nanosheets and the polymer binder affect the final thin film properties? In addition to the nacre-like structure and properties, the researchers also aim to further expand the scope to the formation of three-dimensional hybrid materials, such as bones, by properly tailoring the microstructure of the organic and inorganic components.