Synergistic Effect of Hybrid Carbon Nanotube–Graphene Oxide as Nanoadditive Enhancing the Frictional Properties of Ionic Liquids in High Vacuum

A remarkable synergetic effect between the graphene oxide (GO) layers and multiwalled carbon nanotubes (MWCNTs) in improving friction and wear on sliding diamond-like carbon (DLC) surfaces under high vacuum condition (10^–5 Pa) and low or high applied load is demonstrated. In tests with sliding DLC surfaces, ionic liquid solution that contains small amounts of GO and MWCNTs exhibited the lowest specific friction coefficient and wear rate under all of the sliding conditions. Optical microscope images of the wear scar of a steel ball showed that GO/MWCNT composites exhibited higher antiwear capability than individual MWCNTs and GO did. Transmission electron microscopy images of nanoadditives after friction testing showed that MWCNTs support the GO layers like pillars and prevent assembly between the GO layers. Their synergistic effect considerably enhances IL-GO/MWCNT composites

Superlubricity Enabled by Pressure-Induced Friction Collapse

From daily intuitions to sophisticated atomic-scale experiments, friction is usually found to increase with normal load. Using first-principle calculations, here we show that the sliding friction of a graphene/graphene system can decrease with increasing normal load and collapse to nearly zero at a critical point. The unusual collapse of friction is attributed to an abnormal transition of the sliding potential energy surface from corrugated, to substantially flattened, and eventually to counter-corrugated states. The energy dissipation during the mutual sliding is thus suppressed sufficiently under the critical pressure. The friction collapse behavior is reproducible for other sliding systems, such as Xe/Cu, Pd/graphite, and MoS₂/MoS₂, suggesting its universality. The proposed mechanism for diminishing energy corrugation under critical normal load, added to the traditional structural lubricity, enriches our fundamental understanding about superlubricity and isostructural phase transitions and offers a novel means of achieving nearly frictionless sliding interfaces