Black Phosphorus Quantum Dots in Aqueous Ethylene Glycol for Macroscale Superlubricity

In this study, black phosphorus quantum dots (BPQDs) have been successfully prepared at a low cost and high yield by the liquid-based high-energy ball milling method. The obtained BPQDs with an average lateral size of 6.5 +/- 3 nm and a thickness of 3.4 +/- 2.6 nm dispersed stably in ethylene glycol (EG). A robust macroscale superlubricity state (mu, 0.002) was achieved under a high contact pressure of 336 MPa via the lubrication of BPQDs-EG aqueous suspension (BPQDs-EG(aq)) at the Si3N4/sapphire frictional interface. The wear rate lubricated by BPQDs-EG(aq) suspension account for 5.96% of that lubricated by EG aqueous solution (EG(aq)), demonstrating the improvement in the antiwear property with the addition of BPQDs. The rolling effect of BPQDs and the low shear stress between the BPQDs interlamination played important roles in the improvement in the antiwear property. The oxidative products of BPQDs (PxOy) contributed to the effective realization of macroscale superlubricity. This work realized macroscale superlubricity at a high contact pressure by combining the BPQDs with special liquid molecules and provided the great potential in industrial applications.