Video Graphene is said to be the wonder material of our age, but it’s largely a 2D affair. Now scientists have made 3D structures out of the stuff that will be an engineer’s dream.
Since the first atom-thick strips of graphene were produced, the substance has shown remarkable properties, including extraordinary strength and conductivity. It also has more unusual uses. Now a team at MIT has used heat and pressure to fuse flakes of graphene sheets into 3D shapes that have 4.6 per cent the density of mild steel and are 10 times as strong.
“They are not very useful for making 3D materials that could be used in vehicles, buildings, or devices,” admitted Markus Buehler, MIT’s McAfee Professor of Engineering. “What we’ve done is to realize the wish of translating these 2D materials into three-dimensional structures.”
The goal of the research, funded in part by the US Office of Naval Research and the Department of Defense, was to discover whether or not graphene could be used as a bulk material to build strong 3D structures that were lighter than air.
The team reports in the journal Science Advances this month that modeling showed that lighter-than-air structures aren't possible without the surrounding air pressure crushing the graphene.
Back to the drawing board. To construct a practical 3D structure out graphene that is super strong and yet still rather light, the boffins turned to gyroids: a sponge-like arrangement invented in the 1970s by NASA engineer Alan Schoen that has no straight lines nor planar symmetries. In mathematical modeling and testing under a hydraulic ram, the team recorded some surprising results that could have wider applications beyond graphene.
In stress testing, plastic gyroid prototypes with thicker walls were able to withstand very heavy loads under the ram before explosively blowing apart. Gyroids with thinner walls crumpled down instead, retaining much structural strength as they did so.
So far, so good. A potentially neat way of arranging graphene into a 3D shape. But this is just lab work for now. Mass-producing the complex graphene gyroid structures is probably beyond traditional manufacturing techniques, the team said: the structures had to be 3D printed for the tests, which has its own limitations.
In future, it may be possible to manufacture the gyroid using a metal or a polymer, coat it with layers of fused graphene, and then remove the molding material to leave the 3D carbon-based structure intact. That’s potentially more practical but some way off. In the meantime, the strength and graduated collapsing properties of gyroid structures could well be useful with other, more prosaic, materials.
“You could either use the real graphene material or use the geometry we discovered with other materials, like polymers or metals,” Buehler said. “You can replace the material itself with anything. The geometry is the dominant factor. It’s something that has the potential to transfer to many things.” ®