Bio Focus: Graphene-based composites achieve microstructural order at atomic scale
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Graphene-based composites achieve microstructural order at atomic scale
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Stacking direction for GO and beta sheets (GO/TR42)
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elik Demirel and Mauricio Terrones and their colleagues at The Pennsylvania State University recently published a study in the journal Carbon (doi:10.1016/j.carbon.2017.03.053) detailing a novel method for creating a layered graphene-based molecular composite that achieves bulk microstructural order, thus overcoming one of the main obstacles facing two-dimensional (2D) materials utilization. At the heart of their strategy was the ability to tune the spacing between the stacked layers with atomic-level precision, where the resulting composite could be integrated into a highly flexible and efficient thermal actuator. The combination of strength and high electrical and thermal conductivities of 2D graphene-based materials provides opportunities for engineering materials applications. However, many of these desirable properties are diminished in bulk materials due to a lack of microstructural organization. When precise microstructural control of 2D materials like graphene is achieved in bulk, the extraordinary properties of such materials can be exploited in composites, layered films, and bio-constructs. With the leaps in performance and efficiency of graphene-based being made in materials like the actuators fabricated by Demirel and Terrones’s team, Demirel predicts that future 2D graphene-based materials will be able to “respond to a variety of external stimuli and self-adapt based on the stimuli, thus laying the foundations for truly smart, robust, selfpowered, and autonomous systems.” The researchers fabricated the novel molecular composite using graphene oxide and an organic matrix that consisted of tandem repeat (TR) proteins inspired by squid ring teeth. The TR protein matrix self-assembled into a layered structure of antiparallel β-sheets, subsequently providing a template of hydrogen bonding locations for graphene oxide with the TR proteins. Each protein layer was only one
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(a) Schematic illustration of vacuum-assisted self-assembly of 2D molecular composites. (b) Image of freestanding molecular composite consisting of graphene oxide (GO) and tandem repeat (TR) protein with 42 kDa molecular weight. (c) Cross-section scanning electron microscope and transmission electron microscope (inset) image of molecular composite consisting of GO and TR protein with 25 kDa molecular weight. (d)(i) Backscattered-electron image, and energydispersive x-ray spectroscopy patterns of (ii) carbon, (iii) oxygen, and (iv) nitrogen for molecular composite consisting of GO and TR protein with 25 kDa molecular weight. Credit: Carbon.
β-sheet-thick, thus allowing for ideal intercalation with the graphene oxide. By simply altering the molecular weight of the TR proteins, the researchers showed that the spacing between the stacked layers can be controlled. Interlayer spacing of 0.4 nm, 0.6 nm, and 0.9 nm was reported with three di
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