Researchers at Virginia Tech University (Blacksburg, Virginia, USA) and Lawrence Livermore National Laboratory (LLNL) (Livermore, California, USA) have developed a novel way to make three-dimensional (3-D) prints of graphene.
In the past, researchers could only print graphene in two-dimensional sheets, or basic structures. But here, engineers say they have unlocked the ability for the 3-D printing of graphene objects at a resolution an order of magnitude greater than before. Because of its strength and high thermal and electricity conductivity, the researchers say 3-D printed graphene objects could be useful in industries such as batteries, aerospace, separation, heat management, sensors, and catalysis.
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 3-D shape, it becomes graphite, commonly known as the “lead” in pencils. Because graphite is simply packed-together graphene, it has subpar mechanical properties, the researchers explain. But if the graphene sheets are separated with air-filled pores, the 3-D structure can maintain its properties. This porous graphene structure is called a graphene aerogel.
“Now a designer can design three-dimensional topology comprised of interconnected graphene sheets,” says Xiaoyu “Rayne” Zheng, an assistant professor at Virginia Tech’s department of mechanical engineering. “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, which they compare to squeezing toothpaste. But that technique could only create simple, stackable objects. “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,” Zheng says. “What we did was to get these graphene layers to be architected into any shape that you want with high resolution.”
To create these new structures, the 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, they then used projection micro-stereolithography to create the desired solid 3-D structure with the graphene oxide trapped in the long, rigid chains of acrylate polymer. Finally, they placed the 3-D structure in a furnace to burn off the polymers and fuse the object together, leaving a lightweight graphene aerogel.
While other processes could print down to 100 μm, the new technique allows researchers to print down to 10 μm in resolution, approaching the size of actual graphene sheets. “We’ve been able to show you can make a complex, 3-D architecture of graphene while still preserving some of its intrinsic prime properties,” Zheng says.
Source: Virginia Tech University, vtnews.vt.edu.