Achieving ultralow friction in polymer-ceramic contacts typically requires complex material modifications or interface engineering. This study demonstrates that exceptional tribological performance can be unlocked through rational lubricant-polymer pairing, without altering the polymer. Specifically, polyetheretherketone (PEEK) lubricated by ethylene glycol (EG) against Si₃N₄ achieves an ultralow, stable coefficient of friction (COF = 0.0087) and exceptional wear resistance (specific wear rate = 0.99 × 10^-6 mm³ N^-1 m^-1), outperforming polymers like PTFE and UHMWPE. A comparative investigation of five polymers reveals that PEEK's superiority originates from a unique interfacial synergy with EG, manifesting as concurrent surface strengthening (≈34% increase in nanohardness) and in-situ formation of a continuous, highly ordered graphitic carbon transfer film on the counterface (lowest I_D/I_G = 0.48). Density functional theory calculations attribute this synergy to a geometrically matched, dual‑site chemisorption between the diols of EG and the carbonyl/ether oxygens on the PEEK backbone (binding energy = -0.01157 Ha), in contrast to the weak physisorption or suboptimal polar interactions observed for other polymers. This work establishes a clear structure‑affinity‑interface‑performance relationship and proposes a paradigm‑shifting design strategy for polymer tribosystems based on molecularly synergistic lubricant selection, paving the way for green, sustainable lubrication in precision engineering and biomedical applications.

The present investigation evaluates the effect of graphite-based filler (GBF) size on the mechanical and tribological performance of polyimide (PI) solid lubricant composites. During dry sliding tribological experiments, micro-, nano-graphite (MG, NG), and ultrathin graphene (GN) additives were considered. The results revealed that atomic-thickness GN outperformed micro- and nano-sized GBF filler in terms of mechanical and tribological performance when added into PI matrix. It was inferred that the GN was able to generate sufficient lubricating phases at the frictional interface due to their small size and ultrathin morphology, which provided them with enhanced tribological properties in comparison with the micro and nano-sized GBF fillers. At the friction interface, GN was oxidized by reciprocating shear force and friction heat and formed a lubricating layer of graphene oxide (GO), as evidenced by Fourier transform infrared (FTIR) and Raman spectroscopy. Atomistic modeling techniques were also used to elucidate the surface/interface lubrication mechanism, where GO was tightly adsorbed at frictional interfaces by van der Waals. The results facilitate better understanding of the size effect on the wear mechanism of solid lubricants.

In this work, as a new type of oil-based additive, a phosphate mixture of (Sr_0.9Ca_0.1)₃(PO₄)₂ and Sr₃(PO₄)₂ (SrP) with a flower-like structure was synthesized. Compared with pure poly-α-olefin-8 (PAO8), when a titanium alloy is lubricated, the use of 20 wt% SrP for lubrication can reduce the coefficient of friction (COF) by 69.89% and the wear rate (WR) by 99.86%. The extraordinary tribological performance was attributed to the deposition of a layer of SrP on the surface of the titanium alloy. On the one hand, the deposition layer formed by SrP can prevent direct contact between friction pairs, protect the surface of the titanium alloy, and prevent adhesion wear of the titanium alloy. On the other hand, the low-shear interlayer sliding of SrP nanosheets inside the deposition layer was beneficial for friction reduction. X-ray photoelectron spectroscopy (XPS) confirmed that after frictional sliding, the active group phosphate in SrP was activated, and other metals were oxidized to produce a series of oxides. In addition, phosphate can form P‒O‒Ti bonds with titanium at the interface, which is the key to SrP deposition and adsorption on the surface of titanium alloys. The SrP additive not only exhibited excellent performance in lubricating titanium alloy discs but also stainless steel 304, 42CrMo, and tin bronze. After lubrication with 20 wt% SrP additive, the wear tracks of stainless steel 304 and 42CrMo were not detected, and WR of tin bronze decreased by 92%. An interface lubrication mechanism has been proposed that may be beneficial for the design and application of new lubricating materials.

In this work, the advantage of Coulomb repulsion in the intermolecular forces experienced by molecules on the solid–liquid nanosized contact interface is taken, and the superior friction-reducing property of Cu₃(PO₄)₂·3H₂O (CuP) oil-based additives has been confirmed for titanium alloy. Three-dimensional (3D) CuP nanoflowers (CuP-Fs) with a strong capillary absorption effect are prepared to achieve the homogeneous mixing of solid CuP and lubricating oil. Lubrication by CuP-Fs additives for titanium alloy, friction coefficient (COF) can be reduced by 73.68%, and wear rate (WR) reduced by 99.69%. It is demonstrated that the extraordinary friction-reducing property is due to the repulsive solid–liquid interface with low viscous shear force originating from Coulomb repulsion between polar water molecules in CuP and non-polar oil molecules. However, any steric hindrance or connection between this repulsive solid–liquid interface will trigger the adhesion and increase the viscous shear force, for example, dispersant, hydrogen bondings, and shaky adsorbed water molecules. Besides, the lamellar thickness of CuP and the molecular size of lubricant both have a great influence on tribological properties. Here the lubrication mechanism based on interface Coulomb repulsion is proposed that may help broaden the scope of the exploration in low-friction nanomaterial design and new lubricant systems.