Graphene is known to be the stiffest and strongest material in the two-dimensional (2D) space. Despite its superior mechanical and electrical properties for engineering applications, graphene does not yet have a large-scale three-dimensional (3D) structure for practical uses. However, it can be used as an elemental building block, with appropriate structural design, to form porous assemblies with low mass density and high strength. Now researchers have used computational synthesis models and 3D printing tools to simulate a 3D graphene assembly with strength that may go up to 10 times of mild steel. They found a unique gyroid structure composed of curved surfaces of individual graphene pieces that can be applied to other materials systems for enhanced mechanical properties.

In a recent issue of Science Advances, a research team led by Markus J. Buehler at the Center for Computational Engineering and Laboratory for Atomistic and Molecular Mechanics at Massachusetts Institute of Technology combined computational modeling and 3D printing to explore potential ways of forming practical 3D graphene structures and to investigate their bulk mechanical properties. “Our work provides a solution [for] fusing nanoscale graphene flakes for large-scale engineering applications,” says Zhao Qin, the lead author of this work, “which is different from graphene’s conventional usage.” By building full atomic models of graphene assembly in molecular dynamics simulations, the researchers demonstrated that they could design the chemical synthesis process of graphene flakes to fuse and produce stable 3D porous bulk graphene assembly with controlled architecture and density.

 

In addition, the systematic calculation of the material strength and stiffness shows that these mechanical features strongly depend on the material density as decided by structural parameters. The team derived a set of scaling laws for the mechanics of 3D graphene assembly based of these computational simulations. 

 

“Such result[s] of the scaling law [are] not only applicable to graphene structures but also to general 3D printed models,” Qin says, “suggesting that it is possible to achieve materials of very different mechanical functions by using a uniform building block but designing different microstructures.” The team used one of the designed gyroid structures to build large-scale 3D models using a high-resolution 3D printer, and the mechanical testing results agree well with the scaling law, suggesting that the mechanics of 3D graphene assembly are scalable.

“It is challenging to assemble 3D graphene bulk materials which could maintain the strength of 2D graphene sheets,” says Zheng Yan, a post-doctoral researcher in the department of materials science and engineering at the University of Illinois, Urbana-Champaign with expertise in the field of graphene materials. “The combination of computation and 3D printing-based experiments revealed that the unusual curvature configurations in 3D graphene foams, instead of the material itself, are the dominant factors for the [observed] unique properties.”

Read the article in Science Advances.