Two hundred times stronger than steel, yet extremely flexible and ultralight, graphene is the world’s first 2D material. At only one atom thick, it is the thinnest material possible, and is also the most conductive material known. These properties and more have led to significant research and development efforts aimed at learning more about the material and exploiting its characteristics.
Graphene was first isolated from graphite, the main component of pencil lead, in 2004 by Professor Andre Geim and Professor Kostya Novoselov at the University of Manchester. Using sticky tape, the pair of researchers peeled off fragments of graphite from a larger lump of the material, then repeatedly divided the flakes until they had a layer with the thickness of only one atom.
Since the initial isolation of graphene, continuing research into its properties has led to a deeper understanding of the material. Today, investigators remain engaged in exploring graphene’s many potential applications, including graphene membranes for energy-efficient water filtration and desalination; high-strength graphene-based composite materials for use in lightweight cars and aircraft; graphene supercapacitors for the storage of large amounts of power; and the world’s smallest transistors, made of graphene, that could lead to faster chips.
Scientists have gained considerable insight into graphene’s qualities already, but much remains to be learned. Developments throughout 2017 have significantly advanced graphene research.
Stronger Than Steel
In a study carried out at MIT and published on January 6 in Science Advances, scientists created a porous three-dimensional form of graphene that is one of the strongest lightweight materials known. With just five percent the density of steel, the material has up to ten times the strength of the commonly used structural metal.
To create the 3D graphene material, flakes of graphene were heated up and compressed together under pressure. The process generated unique shapes known as gyroids within the structure of the sponge-like material. These complex shapes, which have a large surface area to volume ratio, are the key to the material’s strength.
To characterize the material’s strength, the researchers performed computational simulations and fabricated scaled-up, plastic 3D models using a 3D printer. In addition to structural support, the porous material might someday find use in water or chemical filtration systems.
In a another study, published on August 21 in Nature Physics, University of Manchester researchers presented a deeper understanding of the physics of electron flow through highly conductive graphene. The scientists found that electrons flowing through graphene constrictions behave like a viscous fluid, improving the material’s conductance to a value higher than the limit established for normal metals by the Landauer-Buttiker formalism.
This “superballistic” viscous flow arises due to electron scattering multiplying collisions between electrons, causing them to work together. This occurs because electrons near the periphery tend to slow down and remain at the edge, creating a buffer that improves flow among the remaining electrons that bounce off of them. This behavior is unexpected, since scattering tends to decrease a substance’s conductivity.
“We know from school that additional disorder always creates extra electrical resistance,” said researcher Andre Geim. “In our case, disorder induced by electron scattering actually reduces rather than increases resistance. This is unique and quite counterintuitive: electrons when make up a liquid [sic] start propagating faster than if they were free, like in vacuum.”
The researchers also found another unanticipated result: graphene conductivity increased with increasing temperature, deviating from the typical metallic behavior expected for doped graphene.
On December 18, in a paper published in Nature Technology, investigators at the City University of New York outlined a method for creating a new ultrahard material they call diamene. The material is comprised of two layers of graphene that undergo a phase change to a film that is as stiff and hard as diamond when exposed to pressure. The phase change is reversible, but is only observed for two-layer graphene stacks; configurations with a single graphene layer or more than two layers do not exhibit the transition.
“Previously, when we tested graphite or a single atomic layer of graphene, we would apply pressure and feel a very soft film. But when the graphite film was exactly two-layers thick, all of a sudden we realized that the material under pressure was becoming extremely hard and as stiff, or stiffer, than bulk diamond,” said Elisa Riedo, the project’s lead researcher. “This is the thinnest film with the stiffness and hardness of diamond ever created.”
The material could find use in lightweight bulletproof films and protective coatings resistant to abrasion.
Steps Toward Commercialization
Graphene continued to make steps out of the lab toward practical applications in 2017. On January 16, the world’s lightest mechanical watch was revealed. Fashioned from a composite case and rubber strap that incorporate graphene, the RM 50-03 watch was the result of a collaboration between The University of Manchester, watchmaking brand Richard Mille and McLaren F1. Comprised of lightweight Graph TPT™ composite, the watch’s durable case endured huge shock damage in tests. The overall weight of the watch is just 40 grams.
The commercialization of products based on graphene took another step forward in 2017 when the first sports footwear incorporating the material was announced on December 6. Partnering with The University of Manchester, British sportswear brand Inov-8 developed an outsole comprised of a mixture of graphene and rubber with improved strength, stretchiness and durability.
“When added to the rubber used in inov-8’s G-Series shoes, graphene imparts all its properties, including its strength,” said Dr. Aravind Vijayaraghavan, reader in nanomaterials at The University of Manchester. “Our unique formulation makes these outsoles 50% stronger, 50% more stretchy and 50% more resistant to wear than the corresponding industry standard rubber without graphene.”
The company plans to bring the shoes to market in 2018.