Macroscale Superlubricity with Ultralow Wear and Ultrashort Running-In Period (∼1 s) through Phytic Acid-Based Complex Green Liquid Lubricants

Abstract

Liquid superlubricity has attracted much attention, due to its ability to significantly reduce friction on the macroscale. However, the severe wear caused by the long running-in period is still one of the bottlenecks restricting the practical application of liquid superlubricating materials. In this work, the obtained polyethylene glycol–phytic acid (PEG–PA) composite liquid lubricants showed outstanding superlubricating properties (μ ≈ 0.006) for Si3N4/glass friction pairs with an ultrashort running-in period (∼1 s) under high Hertzian contact pressure of ∼758 MPa. More importantly, even after up to 12 h (∼700 m of travel), only about 100 nm deep wear scars were found on the surface of the glass sheet (wear rate = 2.51× 10–9 mm3 N–1 m–1). From the molecular point of view, the water molecules anchored between the two friction pairs have extremely low shear force during the friction process, and the strong hydrogen bond interaction between PEG and PA greatly improves the bearing capacity of the lubricant. This work addresses the challenge of liquid superlubricant simultaneously exhibiting low shear force and high load-carrying capacity and makes it possible to obtain liquid superlubrication performance with an extremely short running-in time.

Competition-Induced Macroscopic Superlubricity of Ionic Liquid Analogues by Hydroxyl Ligands Revealed by in Situ Raman

“…At high humidity (70–80%), the superlubricity life was only 35 min, while it was extended to 140 min at low humidity (10–20%) (Figure S4), indicating that a low humidity is more favorable for the achievement of superlubricity. Compared with most previous superlubricity materials (e.g., silicone oil, ILA/H 2 O, glycerol-PG, and B-PEG), ,,− ILA 1:2 has a shorter running-in time (160 s) and higher load-bearing capacity (Figure f).…”

Accelerating Macroscale Superlubricity through Carbon Quantum Dots on Engineering Steel Surfaces

“…Pure water exhibited a high friction coefficient of about 0.284, likely due to its low viscosity and inability to promptly form an effective lubricating film to reduce friction. [7,30] When pure PEG solution was used as a lubricant, the friction coefficient gradually decreased to around 0.17-0.19 owing to the hydrodynamic lubrication and the decrease in actual contact pressure between the friction pairs. [48] The friction coefficient for the PEG-CA solution containing 0.1 wt% CA gradually decreased to less than 0.01 after a runningin period of approximately 800 s and entered a superlubricating state.…”

“…The C 1s fine spectrum revealed peaks corresponding to C═O (288.3 eV), C─O (286.3 eV), and C═C/C─C (284.8 eV) chemical bonds, indicating the presence of PEG, CA or CQDs from the lubricant on the surface of the wear area (Figure 3j). [7,40] The O 1s peaks located at 532.5 eV, 531.3 eV, and 529.3 eV were attributed to the C═O/C─O bond, O─H bond, and Fe─O bond, respectively. The presence of the Fe─O bond suggests the existence of oxygen-containing iron compounds on the friction pair surface (Figure 3k).…”

“…[1][2][3][4] Superlubricity refers to the lubricating state in which the friction coefficient is less than 0.01, making it possible to realize near-zero friction and near-zero wear, and is a feasible strategy to achieve the goals of carbon peak and carbon neutrality. [5][6][7][8][9][10] Solid superlubricity, based on 2D layered materials, such as molybdenum disulfide, [11][12][13] graphene, [14][15][16][17] and highly oriented pyrolytic graphite, [18] have been reported one after another. Unfortunately, the realization of most solid superlubricity usually requires strict conditions, such as perfect crystal quality, vacuum or inert atmosphere, and complex surface structures.…”

“…Nonetheless, these liquid superlubricants typically require a long running-in period, resulting in significant wear before achieving the superlubricating state. [7,31,32] 2D nanoflake additives like black phosphorus, [24,33] graphene oxide, [34] layered bimetallic hydroxides, [35] and MXene [36] have been shown to effectively shorten the running-in time for liquid superlubricity and thus reduce unnecessary wear of friction pairs due to the weak interlaminar shear interaction of 2D nanoadditives or the fast adsorption to the surface of the friction pairs. However, all of the liquid superlubricants containing nanoadditives mentioned earlier still need a long running-in period (>300 s) before achieving superlubricity, and most of the above strategies are only applicable to inert and high-hardness ceramic friction pairs such as Si 3 N 4 , SiO 2 , and sapphire (Al 2 O 3 ).…”