A team of scientists at Virginia Tech and Lawrence Livermore National Laboratory has developed a new 3D printing process to create complex objects out of graphene, one of the strongest materials ever tested on Earth. Their work appears in the journal Materials Horizons.
Hensleigh et al developed a new process to 3D print graphene structures. Image credit: Hensleigh et al, doi: 10.1039/C8MH00668G.
Graphene is an atomically thin, 2D carbon material with exceptional properties including a large specific surface area and impressive electrical conductivity.
When graphene sheets are neatly stacked on top of each other and formed into a 3D shape, it becomes graphite.
Because graphite is simply packed-together graphene, it has fairly poor mechanical properties. But if the graphene sheets are separated with air-filled pores, the 3D structure can maintain its properties. This porous graphene structure is called a graphene aerogel.
“Now a designer can design 3D topology comprised of interconnected graphene sheets,” said Dr. Xiaoyu ‘Rayne’ Zheng, of Virginia Tech.
“This new design and manufacturing freedom will lead to optimization of strength, conductivity, mass transport, strength, and weight density that are not achievable in graphene aerogels.”
Previously, researchers could print graphene using an extrusion process, but that technique could only create simple objects that stacked on top of itself.
“With that technique, there’s very limited structures you can create because there’s no support and the resolution is quite limited, so you can’t get freeform factors,” Dr. Zheng said.
“What we did was to get these graphene layers to be architected into any shape that you want with high resolution.”
To create complex graphene structures, the scientists started with graphene oxide, a precursor to graphene, crosslinking the sheets to form a porous hydrogel.
Breaking the graphene oxide hydrogel with ultrasound and adding light-sensitive acrylate polymers, they could use projection micro-stereolithography to create the desired solid 3D structure with the graphene oxide trapped in the long, rigid chains of acrylate polymer.
Finally, they would place the 3D structure in a furnace to burn off the polymers and fuse the object together, leaving behind a pure and lightweight graphene aerogel.
“We created graphene structures with a resolution an order of magnitude finer than ever printed,” they said.
“Other processes could print down to 100 microns, but the new technique allows us to print down to 10 microns in resolution, which approaches the size of actual graphene sheet,” said Ryan Hensleigh, Ph.D. student at Virginia Tech.
“We’ve been able to show you can make a complex, 3D architecture of graphene while still preserving some of its intrinsic prime properties,” Dr. Zheng said.
“Usually when you try to 3D print graphene or scale up, you lose most of their lucrative mechanical properties found in its single sheet form.”
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Ryan M. Hensleigh et al. Additive manufacturing of complex micro-architected graphene aerogels. Materials Horizons, published online August 13, 2018; doi: 10.1039/C8MH00668G
