Friction between moving parts and the associated wear are responsible for about 25% of the world’s energy consumption. Superlubricity is a new mechanism of ultralow friction between solid surfaces, achieved with 2D materials such as graphene. When the atomic valleys are in incommensurate alignment (as illustrated in the title image), the atomic forces balance, and the friction coefficient drops to ultralow values. While the superlubric properties of ideal flat graphene surfaces has been measured in the lab, it has poorly been explored in applications. In the EU project SSLiP, we aim to lift superlubricity to the macroscopic scale. The idea is to use particles coated with superlubric material such as graphene or MoS2 to obtain a lubricant that can be used in applications at large scale. This requires understanding of not only of the superlubric mechanism, but also of the flow properties and structure of the superlubric particles under mechanical excitation. To obtain insight, we combine measurement of the resistance of these particles to shear with direct imaging of their structure and contacts using 3D confocal microscopy. This technique allows tracking the individual particles during applied deformation to reconstruct their flow fields. To image the contact network, we will explore the natural fluorescence of the 2D materials, which becomes quenched when 2D material layers are in contact. These microscopic observations should give insight into the micromechanics of ultralow-friction lubricants.
Commensurate (left) and incommensurate alignment (right) of graphene lattices. In the incommensurate alignment, the atomic forces balance and superlubric sliding occurs.