Researchers at Northwestern University targeted the problem of fuel waste in automobiles due to friction, and tested crumpled graphene balls as a lubricant additive. In a series of tests, oil modified with crumpled graphene balls outperformed some commercial lubricants by 15%, both in terms of reducing friction and the degree of wear on steel surfaces.
Crumpled graphene balls are a novel type of ultrafine particles that resemble crumpled paper balls. The particles are made by drying tiny water droplets with graphene-based sheets inside. The scientists explain that capillary force generated by the evaporation of water crumples the sheets into miniaturized paper balls, just like how we might crumple a piece of paper with our hands.
Nanoparticles, particularly carbon nanoparticles, have been previously studied to help increase the lubrication of oil. The particles, however, usually do not disperse well in oil and instead tend to clump together, which makes them less effective for lubrication. The particles may jam between the gear's surfaces causing severe aggregation that increases friction and wear. To overcome this problem, past researchers have modified the particles with extra chemicals, called surfactants, to make them disperse. But this still doesn't entirely solve the problem as surfactant molecules can rub off and decompose, making the particles clump up again.
Their unique shape makes crumpled graphene balls self-disperse without needing surfactants, as their pointy surfaces render them unable to make close contact with other graphene balls. Even when they are squeezed together, they easily separate again when disturbed.
The team also found that performance of crumpled graphene balls is not sensitive to their concentrations in the oil, while for all other carbon additives, such performance is very sensitive to concentration. Next, the team plans to explore the additional benefit of using crumpled graphene balls in oil: they can also be used as carriers. Because the ball-like particles have high surface area and open spaces, they are good carriers for materials with other functions, such as corrosion inhibition.
In October 2011, researchers from Northwestern University discovered that crumpling graphene sheets into balls exhibits strain-hardening behaviors. In October 2014, MIT scientists discovered that crumpling graphene paper (made from graphene sheets bonded together) results in a low-cost material that is very useful for extremely stretchable supercapacitors for flexible devices.