Achieving macroscale liquid superlubricity using glycerol aqueous solutions

In this work, we explored macroscale liquid superlubricity using glycerol as the base lubricant to form aqueous solutions with different water/glycerol weight ratios. We find that glycerol aqueous solutions with water/glycerol weight ratio of 0.2 achieves superlubricity (coefficient of friction < 0.01) reproducibly within 40 s of testing using steel tribopairs, under a modest range of tribotesting conditions (maximum nominal Hertzian stress up 800 MPa and sliding speed up to 0.15 m/s). Mixed-elastohydrodynamic simulation reveals evidence of apparent mating between asperities on the ball and the disk, along with the formation of microscopic elastohydrodynamic lubrication films that are thick enough to separate the tribopair asperities. The numerical simulation also gives the limiting superlow coefficient of friction. These results lead to a hypothesis by which superlubricity could be achieved with other lubricants.