Nanoporous graphene: High strength and flexibility achieved
Excellent tensile strength and ductility have been realized in an ultralight, three-dimensional structure made of nanoporous graphene
An ultralight, graphene-based material that is both extremely strong and ductile has been developed by AIMR researchers1. These properties make the material promising for a wide range of applications, including those in the aerospace and automotive industries.
Graphene’s strength is well documented — the flat sheet of carbon atoms arranged in a hexagonal honeycomb lattice is one of the strongest materials discovered to date, hundreds of times stronger than steel. But it has been challenging to use graphene’s two-dimensional strength to form strong three-dimensional structures, particularly those that can withstand tension (forces that seek to pull the structures apart), because graphene’s strength is reduced if it contains any defects. In addition, adjacent graphene sheets are held together by weak Van-der-Waal bonds.
Furthermore, it has been difficult to realize lightweight, carbon-based materials that are both strong and ductile.
Now, inspired by the structures of recently developed artificial materials known as metamaterials, Hamzeh Kashani and Mingwei Chen of the AIMR at Tohoku University and their colleagues have made an ultralight graphene structure containing nanoscale pores that has an excellent tensile strength and ductility.
“Metamaterials are artificially engineered structures on the microscale or nanoscale whose unique properties stem mainly from their structure rather than the properties of their constituent materials,” says Kashani. “By using this concept and employing a bicontinuous, nanoscale architecture, we were able to shape a single sheet of graphene into a three-dimensional structure.”
The team produced centimeter-sized pieces of the material by growing graphene on a nickel block that contained nanosized pores. They then stripped away the nickel by etching, so that only a three-dimensional seamless tubular network of graphene remained (see image).
The secret to the material’s simultaneous strength and flexibility lies in the fact that the graphene structural elements can both stretch with an extremely high in-plane strength and bend with out-of-plane flexibility. “Lightweight porous structures that deform with stretching-dominated modes show higher strength and stiffness, whereas those with bending-dominated modes have lower strength and stiffness but offer more flexibility and ductility,” explains Kashani. “Our material can respond to loads in entirely new ways through a combination of stretching and bending deformation modes.”
The results have broader implications for two-dimensional materials besides graphene. “Our work demonstrates that the two-dimensional properties of materials can be exploited by judicious design of the architecture of three-dimensional nanostructures,” says Kashani.
The team now intends to improve the physical and mechanical properties of composite materials by using their graphene material to reinforce metal and polymer matrices.
- Kashani, H., Ito, Y., Han, J., Liu, P. & Chen, M. Extraordinary tensile strength and ductility of scalable nanoporous graphene. Science Advances 5, eaat6951 (2019). | article
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