Lubricity is a measure of how much a lubricant reduces mechanical friction and wear in moving parts. Given that a lack of lubricity is a major cause of component failure in mechanical and electromechanical systems as well as a drain on energy, there are ongoing efforts to find improved lubricants and even materials that might be said to offer superlubricity. A superlubricant that essentially made friction between moving parts negligible would simultaneously make for ultra-low wear but reduce energy costs in a wide range of devices.

Now, a joint venture between researchers at Tel Aviv University and Tsinghua University has demonstrated that structural superlubricity can be achieved between dissimilar, microscale-layered materials even under high external loads and ambient conditions. The researchers showed that the microscale interface between graphite and hexagonal boron nitride can have ultra-low friction and so ultra-low wear. They suggest that this is an important milestone on the road to future technological applications in the automotive industry, in electronics, medicine, and in space exploration.

TAU chemists Oded Hod and Michael Urbakh and mechanical engineer Ming Ma and Quanshui Zheng of Tsinghua University and their colleagues published details at the end of July [Hod, O. et al. Nature Mater (2018) DOI: 10.1038/s41563-018-0144-z]. The team defines structural superlubricity as "a fascinating tribological phenomenon, in which the lateral interactions between two incommensurate contacting surfaces are effectively cancelled resulting in ultralow sliding friction." The new interface is six orders of magnitude larger in surface area than earlier nanoscale measurements and exhibits superlubricity in all interfacial orientations and under ambient conditions, the team reports. Urbakh explains that, "This can be also used in a new generation of ball bearing to reduce rotational friction and support radial and axial loads. Their energy losses and wear will be significantly lower than in existing devices."

The team carried out experiments on their superlubricant using atomic force microscopy (AFM) at Tsinghua and also fully atomistic computer simulations at TAU. They characterized the degree of crystallinity of the graphitic surfaces using spectroscopy.

"These two materials [graphene and hexagonal boron nitride] are currently in the news following the 2010 Nobel Prize in Physics, which was awarded for groundbreaking experiments with the two-dimensional material graphene," Hod says. "Superlubricity is one of their most promising practical applications." Moreover, the results suggest that this phenomenon is of a general nature and should have application with other two-dimensional, van der Waals heterostructures, the work suggests.

David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase. His popular science book Deceived Wisdom is now available.