Researchers from Virginia Tech and Lawrence Livermore National Laboratory have developed an innovative method to 3D print graphene, which until now has only been available in 2D sheets or basic structures.
According to engineers at Virginia Tech, they have been able to 3D print graphene objects at a resolution and an order of magnitude greater than ever before, unlocking the ability to, in theory, create any size or shape of graphene.
Graphene is extremely strong and has high thermal and electricity conductivity. 3D printed graphene objects would be welcomed by a number of industries, including batteries, aerospace, separation, heat management, sensors, and catalysis.
A single layer of carbon atoms organised 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. 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.
"Now a designer can design three-dimensional topology comprised of interconnected graphene sheets," said Xiaoyu "Rayne" Zheng, assistant professor with the Department of Mechanical Engineering in the College of Engineering and director of the Advanced Manufacturing and Metamaterials Lab. "This new design and manufacturing freedom will lead to optimisation of strength, conductivity, mass transport, strength, and weight density that are not achievable in graphene aerogels."
Zheng, also an affiliated faculty member of the Macromolecules Innovation Institute, has received grants to study nanoscale materials and scale them up to lightweight and functional materials for applications in aerospace, automobiles, and batteries.
Researchers have printed graphene using an extrusion process, but that technique could only create simple 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 explained. "What we did was to get these graphene layers to be architected into any shape that you want with high resolution."
To create these complex structures graphene oxide sheets, a precursor to graphene, is crosslinked to form a porous hydrogel. Breaking the graphene oxide hydrogel with ultrasound and adding light-sensitive acrylate polymers, micro-stereolithography is used to create a solid 3D structure with the graphene oxide trapped in the long, rigid chains of acrylate polymer. The 3D structure is then placed in a furnace to burn off the polymers and fuse the object together, leaving behind a pure and lightweight graphene aerogel.
"We've been able to show you can make a complex, three-dimensional 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 their lucrative mechanical properties found in its single sheet form."