Macroscale liquid superlubricity achieved with mixtures of fructose and diols

Abstract

Superlubricity has numerous benefits in industrial applications, but its practical applications are restrained from its heavy dependence on special atmosphere environment and the use of low-dimensional materials. This paper reports a novel and facile method to macroscale liquid superlubricity for steel tribopairs, which realizes superlow friction almost right at the start of the test. Two diols of ethylene glycol (EG) and 1,3-propanediol (13-PD) are used as the base lubricants, and fructose is dissolved into two diols at various fructose/diol weight ratios. Then the tribological properties of the prepared lubricant solutions have been investigated. Friction test results suggest that the lubricant solutions of fructose and EG with the fructose/EG weight ratio of 0.5 is capable of realizing stable and robust superlubricity combined with little wear under a certain range of testing conditions for steel tribopairs. Such desirable superlubrication state can be attributed to three main factors: (1) formation of a desirable hydrodynamic lubricant film between the tribopairs to support the load and separate the rubbing surfaces; (2) effective passivation effect to the asperity contact sites at the interface by forming robust slippery layers of fructose and diol molecules; (3) tribological polishing effect to make the contacting surfaces smooth. Lubricant solutions of fructose and 13-PD with the fructose/13-PD weight ratio of 0.3 is also found to behave near superlow friction and negligible wear, allowing it to replace fructose/EG = 0.5 in certain applications where both superlow friction and human safety are greatly concerned.