Aug 24, 2018 | By Thomas
Researchers from the Virginia Tech College of Engineering and Lawrence Livermore National Laboratory have developed a novel process to 3D print graphene, one of the highest-performing materials used in aerospace, energy storage and insulation.
Image Credit: Virginia Tech
Graphene is a single layer of carbon atoms organized in a hexagonal lattice. When graphene sheets are neatly stacked on top of each other and formed into a three-dimensional shape, it becomes graphite, commonly known as the “lead” in pencils.
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 three-dimensional structure can maintain its properties. This porous graphene structure is called a graphene aerogel.
Previously, researchers could only 3D print graphene aerogel using direct-ink or other extrusion-based methods. Bt 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,” said Xiaoyu “Rayne” Zheng, former LLNL Lab staff scientist, now an assistant professor in mechanical engineering at Virginia Tech. “What we did was to get these graphene layers to be architected into any shape that you want with high resolution.”
Three years ago, scientists and engineers at Lawrence Livermore National Laboratory (LLNL) and Virginia Tech began focusing on 3D printing graphene aerogel using light, a method known as projection micro-stereolithography.
In projection micro-stereolithography, ultraviolet light is used to project an image of a part layer into a photosensitive liquid resin, which is cured and hardened into the shape of the image. Using this method, researchers were able to reduce the resolution in 3D graphene aerogels printed through extrusion-based methods from around 100 microns to about 10 microns.
To create these complex structures, researchers 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, researchers 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 placed the 3D structure in a furnace to burn off the polymers and fuse the object together, leaving behind a pure and lightweight graphene aerogel.
Zoomed in graphene octet truss on strawberry blossom. Image Credit: Virginia Tech
One of the major challenges of the project was coming up with a graphene aerogel resin compatible with the micro-stereolithography process. Ryan Hensleigh, a summer intern at LLNL who is pursuing his Ph.D. at Virginia Tech in macromolecular science and engineering, said he worked on numerous chemical mixtures over a period of two years before finding the right combination.
“It’s a significant breakthrough compared to what’s been done,” Hensleigh said. “We can access pretty much any desired structure you want.” The ability to print complex structures from graphene aerogel also opens the door to numerous applications that could benefit from computer-driven optimized design, such as aerospace, reactors, desalination plants and chemical processing.
“We’ve been able to show you can make a complex, 3D architecture of graphene while still preserving some of its intrinsic prime properties,” Zheng said. “Usually when you try to 3D print graphene or scale up, you lose most of the lucrative mechanical properties found in its single sheet form.”
Scientists and engineers are now looking to boost the surface area of 3D-printed parts and will do further research to determine precise parameters to further optimize the technology.
The key finding of this work was recently published in the journal Materials Horizons.
Posted in 3D Printing Application
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