July 28th, 2015

Chalk another amazing ability up for the supermaterial graphene. It seems the atom-thick sheets of linked carbon atoms can virtually eliminate friction.

The simulation above depicts the graphene-lubricant discovery–blue graphene sheets roll up to encase gold nanodiamonds as a surface of black diamond-like carbon slides over. Once the graphene wraps into so-called nanoscrolls around the nanodiamonds, the sheets make friction disappear.

“The nanoscrolls combat friction in very much the same way that ball bearings do by creating separation between surfaces,” said Argonne National Lab researcher Sanket Deshmukh. Learn more and see photos below.

Researchers say the nanoscrolls offer a totally new mechanism to achieve the condition of superlubricity, a state in which the friction that naturally occurs when two objects slide past each other disappears.

Any lubricant that can help a machine’s parts achieve this state in the real world would revolutionize engineering because of the energy savings and reducing wear on components. According to the Society of Tribologists and Lubrication Engineers, friction consumes up to half of the total energy produced in the world. Costs associated with the wearing down of machine parts because of friction in the U.S. can total two-thirds of the country’s energy costs. On a smaller scale, the energy it takes for the typical automobile to overcome friction and get moving burns about a third of every tank of fuel.

(This large-scale simulation depicts a phenomena called superlubricity, or a condition of extremely low friction. The simulation reveals that this condition originates at the nanoscale when graphene atoms self-assemble into a tube-like scaffolding that reduces contact area and friction. The gold represents nanodiamond particles; the red is a graphene nanoscroll; green shows underlying graphene on silicon dioxide; and the gray structure is the diamond-like carbon interface. Image and caption courtesy of Sanket Deshmukh, Joseph Insley, and Subramanian Sankaranarayanan, Argonne National Laboratory.)

Using a supercomputer at Argonne, a team recreated experiments that had previously shown that graphene sheets sliding against a steel ball coated with diamond-like carbon produced very little friction. The experimental results, however, showed inconsistencies when the experiment took place in humid environments.

Their simulation revealed that the graphene nanoscrolls that rolled up would collapse under the weight of the steel ball, causing friction to spike. To remedy the instability, they added nanodiamonds into the simulation mix, which stabilized the graphene nanoscrolls when they were rolled up into them.

The group tried the simulation’s remedy in a new round of experiments, which proved successful at sustaining the superlubricity state.

“The beauty of this particular discovery is that we were able to see sustained superlubricity at the macroscale for the first time, proving this mechanism can be used at engineering scales for real-world applications,” said computational nanoscientist Subramanian Sankaranarayanan.

The material has a major limiting factor–it stops working in the presence of water. Argonne is working on a solution that would help it repel water but, in the meantime, it has a number of potential uses in dry environments from spinning computer hard drives to wind turbine gears and other dry mechanical systems.

“Friction and wear remain as the primary modes of mechanical energy dissipation in moving mechanical assemblies; thus, it is desirable to minimize friction in a number of applications,” the authors write in a study published recently in the journal Science. “We demonstrate that superlubricity can be realized at engineering scale when graphene is used in combination with nanodiamond particles and diamondlike carbon. Macroscopic superlubricity originates because graphene patches at a sliding interface wrap around nanodiamonds to form nanoscrolls with reduced contact area that slide against the DLC surface, achieving an incommensurate contact and substantially reduced coefficient of friction.”

Top gif: Argonne scientists used the Mira supercomputer to identify and improve a new mechanism for eliminating friction, which fed into the development of a hybrid material that exhibited superlubricity at the macroscale for the first time. This animation depicts the mechanism in which graphene patches (blue) spontaneously roll around nanodiamonds (gold) to enable sustained superlubricity. Gif created from Youtube video. Courtesy of Argonne National Lab.