Graphene, a single layer of graphite with the atoms arranged in a honeycomb-like hexagonal pattern, is one of the theoretically toughest materials in the known universe. Not content with that billing, however, materials scientists from Rice University in Houston, Texas, have found a way to make it more than twice as tough — courtesy of embedded carbon nanotubes. In three-dimensional graphene structures, they have demonstrated that it’s possible to strengthen it by up to 10 times.
“We have shown that we can grow graphene with nanotubes,” James Tour, professor of materials science and nano-engineering at Rice University, told Digital Trends. “We call this rebar graphene, with ‘rebar’ being the metal bars that go through concrete to strengthen it.”
The problem, Tour explained, is that while graphene is 100 times the strength of steel, regular pristine graphene can also end up tearing at defect sites due to its extreme thinness. This means that graphene has never reached its theoretical maximum in terms of durability. By embedding carbon nanotubes during the graphene formation process, it’s possible to develop reinforced graphene which reduces the effects of cracks.
The rebar graphene was made by spin-coating single-walled nanotubes onto a copper substrate, and then growing the graphene around it using a process of chemical vapor deposition. “This leads to a covalent chemical linkage between the graphene sheets and the nanotubes,” Tour continued.
The new reinforced graphene process doesn’t add yet more potential applications to the immensely versatile super-material, but rather makes existing use cases more feasible — since graphene’s real-world effectiveness can only be truly measured by its weakest link. “It allows you to do things with graphene which you may have intended to do before, but were unable [to],” Tour said.
In previous tests, researchers from Rice University have shown that graphene has a native fracture toughness of 4 megapascals. In contrast, rebar graphene has an average toughness of 10.7 megapascals. As noted, this difference is even more noticeable in 3D graphene-based structures the lab has engineered.
Next up, Tour said the team is focused on ways to scale the manufacturing process, thereby making this a practical discovery, as opposed to one primarily of interest to researchers in the lab. “What I want to see next is scaling to machines that can do this rapidly, using systems that can fabricate graphene in this toughened form,” he said. “That’s really going to change things, and that’s where we’re going.”
A paper describing the work was recently published in the journal ACS Nano.