Achieving Macroscale Liquid Superlubricity Using Lubricant Mixtures of Glycerol and Propanediol

Friction and wear are ubiquitous in moving mechanical systems, and achieving vanishing friction and wear could significantly improve the energy efficiency and extend the service life of mechanical components. In this paper, two types of propanediol, viz. 1,3-propanediol (13-PD) and 1,2-propanediol (12-PD), have been selected to be mixed with glycerol for superlubricity performance. The results show that the lubricant mixture of 13-PD and glycerol (13-PD/glycerol) is effective in providing superlow friction (COF < 0.01) for steel tribopairs under an ambient atmosphere environment with little surface damage caused. However, 12-PD that exhibits the same chemical formula as 13-PD except for the configuration of hydroxyl groups is ineffective in superlubricity achievement. Experimental and molecular dynamics simulation results show that the superlow friction realized by the lubricant mixture of glycerol and 13-PD is related to the enhanced intermolecular hydrogen-bonding interaction and the formation of adsorbed molecular layers. The intermolecular interaction strength is related to the rheological property of lubricant mixtures, while the formation of adsorbed molecular layers affects the passivating efficiency of the interactions between opposite surfaces. Compared with 12-PD, the hydroxyl groups of 13-PD are more exposed for intermolecular interaction. This paper could help provide a guideline to the design of novel lubricants for superlubricating performance and push the development of liquid superlubricity for future engineering applications.