Investigation of Superlubricity Achieved by Polyalkylene Glycol Aqueous Solutions

Ultralow friction coefficient (μ) of a polyalkylene glycol (PAG) aqueous solution obtained in both droplet state (40 μL) and full immersion state after a running‐in period. Here, two key factors in achieving the superlubricity state (μ < 0.01) demonstrated: the low shearing strength of the hydrated layer and the presence of a suitable amount of free water molecules. In the initial running‐in period, a decrease in contact pressure contributes to the formation of elastohydrodynamic behavior of fluid. The hydrogen‐bonded PAG chains produce a hydrated layer between two sliding solid surfaces so as to lower the shear strength. The presence of free water molecules effectively weakens interactions between polymer chains. Therefore, the superlubricity state can be realized over a wide range of concentrations (30–60 wt%). Present work shows the mechanism of a stable lubricating system with superior tribological properties, and has a significant potential in industrial applications.