Jiusheng Li

The increasing global concern over environmental issues has presented significant challenges to traditional lubricant additives that contain sulfur, phosphorus or metal components. Accordingly, the development and application of sulfur- and phosphorus-free lubricant additives have become an important research direction. Due to the absence of the aforementioned harmful elements, crown ether compounds show a significant competitive advantage as lubricant additives. In this study, two benzoazacrown ether derivatives were designed and synthesized, and their performance as organic friction modifiers (FMs) in low-viscosity base oil was systematically investigated. The results reveal that benzoazacrown ether derivatives bearing multiple oxygen and amide binding sites display distinct tribological behaviors, which are governed by the type of side-chain alkyl groups. Compared with the conventional benzocrown ether derivative (LC-BCE18-6), the amide-functionalized benzoazacrown ether derivatives achieve superior tribological performance. Among them, the benzoazacrown ether derivative with a long linear alkyl side chain (LC-Aza-BCE18-6) delivers the most prominent friction reduction, with its friction coefficient decreasing by 17.4% and wear rate decreasing by 50.1% compared with the base oil. Such excellent performance originates from the effect of polar adsorption sites and long linear alkyl groups. When the molecules adsorb onto the friction surface via the nitrogen-containing crown ether ring, the long linear alkyl chains can arrange orderly to form a stable adsorbed film. During friction, these adsorbed films further undergo tribochemical reactions to produce protective tribofilms, which further reinforce the friction-reducing and anti-wear capabilities.

Fretting can cause severe adhesive wear in aluminum alloy contacts and impair the performance of precision components. This study combines an ionic liquid-gold (IL-Au) colloidal lubricant with aluminum oxide films that provide both a hard barrier and a lubricant reservoir. In reference tests on 7075 aluminum alloy, the combined system reduced the coefficient of friction to about 0.12, 88% below the unlubricated alloy (1.01) and well below either component alone. Under the same lubricant, the four oxide treatments behaved differently mainly at the higher frequency: at 100 Hz the two hard-anodized films still held about 0.12, whereas the chromic-acid-anodized film failed early and the micro-arc oxidation coating gave higher friction despite remaining unpenetrated. These differences reflected coating integrity, load-bearing topography, and lubricant availability. Beyond these factors, XPS revealed surface species consistent with tribochemical decomposition of the ionic liquid anion to form a protective tribofilm. The crack-free HA-50m film combined low friction with resistance to cracking, making it a promising candidate under the tested conditions. Coating integrity and lubricant availability should therefore be considered together when selecting oxide surfaces for fretting contacts under limited lubricant supply.

Conventional poly-α-olefin (PAO) base oils are widely used in grease formulations, but how their degree of polymerization affects oil-phase confinement and release within polyurea thickener networks at elevated temperatures remains unclear. Here, PAO20, PAO40, and PAO100 were used to prepare PGA, PGB, and PGC, respectively, each containing 10 wt % of the same preformed polyurea thickener. Microscopy and X-ray scattering characterized thickener swelling, network aggregation, and local packing. Rheological measurements assessed network strength, LF-NMR at 125 °C assessed oil-phase mobility, and pressure oil-separation tests quantified oil release after high-temperature treatment. PGA exhibited the greatest thickener swelling and network dispersion, together with the highest oil-phase mobility and oil separation (13.29 wt %). PGC showed more pronounced fiber aggregation, the highest rheological strength, the most restricted oil-phase mobility, and the lowest oil separation (0.60 wt %). PGB exhibited intermediate oil-phase mobility, oil separation (8.43 wt %), and network strength. At 125 °C, 35 N, and 5 Hz, PGB showed the shortest running-in period (876 s), the lowest whole-test average coefficient of friction (0.130), and the narrowest wear scar (1470 μm), together with reduced metal transfer and a lower metal-oxide contribution on the worn surface. Tribological performance therefore did not vary monotonically with PAO polymerization degree: neither the highest oil-phase mobility nor the strongest oil confinement corresponded to the lowest friction and wear. These findings provide a physicochemical basis for selecting conventional PAO base oils for polyurea greases under the investigated elevated-temperature conditions.

Reliable lubrication is essential for maintaining the operation of water‐exposed frictional interfaces in marine, offshore, and wet mechanical systems. However, rapid lubrication restoration after local lubricant depletion or interfacial failure remains challenging because wet environments simultaneously disrupt substrate attachment and destabilize interfacial lubricant retention. Here we report a flexible self‐lubricating organogel patch (SLOP) as a press‐on material for post‐damage lubrication restoration and temporary surface protection in water environments. SLOP is prepared by photopolymerizing lauryl acrylate in polyalphaolefin oil, forming a soft, shape‐adaptable patch with a covalently crosslinked oil‐retaining polymer network. This material overcomes the fundamental contradiction between adhesion and lubrication in interfacial interactions by introducing a shear‐responsive oil redistribution mechanism. Under wet static conditions, the compliant organogel maintains attachment through conformal contact and multiple interfacial interactions. During sliding, localized shear causes the deformation of the polymer network in SLOP and drives the confined oil phase to move toward the sheared interface, generating a lubricating film and achieving a low coefficient of friction (∼0.05) in artificial seawater. The hydrophobic matrix further limits water and ion ingress, contributing to corrosion mitigation under saline exposure. SLOP therefore provides a deployable platform for restoring low‐friction function at representative water‐exposed frictional interfaces.