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September 20, 2011

Grafold - folded graphene can take 5 to 12 times more compression

Nanotechnology journal - Mechanical properties of grafold: a demonstration of strengthened graphene

In this paper, the mechanical properties of grafold, an architecture of folded graphene nanoribbon, are investigated via molecular dynamics simulations and
intriguing features are discovered. In contrast to graphene, grafold is found to develop large deformations upon both tensile and compressive loading along the longitudinal direction. The tensile deformation is plastic, whereas the compressive deformation is elastic and reversible within the strain range investigated. The calculated Young’s modulus, tensile strength, and fracture strain are comparable to those of graphene, while the compressive strength and strain are much higher than those of graphene. The length, width, and folding number of grafold have distinctive impacts on the mechanical performance. These unique behaviors render grafold a promising material for advanced mechanical applications

Researchers’ simulations showed that grafold is “harder” than graphene and can withstand much larger amounts of compression (10-25 GPa depending on the structure of grafold compared with less than 2 GPa for graphene). While its compressive strength is significantly higher than that of graphene, grafold’s tensile strength approaches that of graphene. The Young’s modulus (a measure of elasticity) and fracture strain of grafold are a little lower than those of graphene. The scientists noted that several other materials can withstand greater compression than grafold, including carbon nanotubes, which can be both elongated and squeezed like grafold.


a) Schematic configuration of a grafold system, GRA70 L60 2folds, double folded. The width and length are 70 °A and 60 A° , respectively. The tensile or compressive deformations will be loaded along the longitudinal direction (z-axis). (b) Illustration of the semi-CNT-like region and the semi-graphene-like region.




In conclusion, through molecular dynamics simulations, we demonstrate that the folding process of the graphene nanoribbon can lead to a novel architecture, termed grafold, with enormous Young’s modulus and tensile strength rivaling those of graphene as well as attractive compressive properties. Under tensile deformation, the strength of the graphene could still be retained in the grafold, and the breakage of the first bond is observed to occur at the junction of the curved and the planar belts, where the interlayer distance is minimum. During compression, the highly curved folding edge provides the vehicle for the buckling, and the deformation is found to be elastic within the strain range studied. After necking, the system can still be squeezed to bear more loadings. The compressive performance of graphene is ‘strengthened’ by the folding process. The direction-dependent, fascinating mechanical behaviors of the grafold suggest that the physical properties of graphene nanoribbons can be tuned by simply folding them into various curved planar configurations. Our simulation results as demonstrated in this work provide a new route for tailoring the functionality of graphene-based nanomaterials.

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