Lubrication Mechanism Research Articles

Perspective of Tribological Mechanisms for α-Alkene Molecules with Different Chain Lengths from Interface Behavior.

Three α-alkene lubricants, differentiated by chain length, were selected as model compounds to investigate the influence of chain length on tribological properties. The novelty of this study lies in setting chain length as the sole variable to explore its impact on surface and adsorption energy. Based on the above findings, the study provides a unique explanation of the intrinsic relationship between chain length and tribological performance. The tribological properties of the three α-alkenes were compared, and subsequent characterization methods elucidated the wear mechanisms and explored tribochemical reactions. The study employed the Owens-Wendt-Rabel-Kaelble (OWRK) method and density functional theory (DFT) to investigate each compound's surface energy and adsorption energy. Experimental results revealed that the average friction coefficients (abridged as COF) for 1-decene, 1-tetradecene, and 1-octadecene decreased sequentially to 0.125, 0.099, and 0.075, respectively. The wear volume of 1-tetradecene decreased by 53.2% and that of 1-octadecene decreased by 64.0% compared to 1-decene. This can be attributed to the simultaneous enhancement of the surface energy and adsorption energy with increasing chain length. On the one hand, the increase in surface energy facilitates tribochemical reactions positively influencing the formation of tribofilms. On the other hand, the increase in adsorption energy enhances the adsorption of lubricants on the substrate surface. The synergy of these two effects allows 1-octadecene and 1-tetradecene (long-chain α-alkenes) to exhibit superior tribological performance compared to that of 1-decene (short-chain α-alkenes). Ultimately, this study offers unique insights into understanding lubrication mechanisms.

Roughness induced variation as a new mechanism for hydrodynamic lubrication between parallel surfaces

Roughness induced variation as a new mechanism for hydrodynamic lubrication between parallel surfaces

Film forming and lubrication mechanisms of whey proteins and mucin

Film forming and lubrication mechanisms of whey proteins and mucin

Tribological performance and lubrication mechanism of phosphate nanoflowers as oil-based additives

Tribological performance and lubrication mechanism of phosphate nanoflowers as oil-based additives

Multi-response Optimization of Tribological Characteristics for Graphene-Gear Oil Nanolubricants Using Grey-Taguchi Methodology Followed by Scrutinization of Lubrication Mechanisms

Multi-response Optimization of Tribological Characteristics for Graphene-Gear Oil Nanolubricants Using Grey-Taguchi Methodology Followed by Scrutinization of Lubrication Mechanisms

Oleylamine-grafted carbon nanoparticles as the friction-reducing and anti-wear additives of aviation lubricating oils

Purpose This paper aims to try to develop new, environmentally friendly and efficient lubricating additives; study the compatibility of carbon-based additives with different base oils [Polyalphaolefin (PAO)-3, PAO-20 and NPE-2]; and explore the lubrication mechanism. Design/methodology/approach Oleylamine modified carbon nanoparticles (CNPs-OA) were prepared and the dispersion stability of CNPs-OA in PAO-3, PAO-20 and NPE-2 base oils was investigated by transmission electron microscopy, Fourier transform infrared, thermogravimetric analysis, energy dispersive spectroscopy and X-ray photoelectron spectroscopy. Universal Mechanical Tester (UMT) platform was used to carry out experiments on the effects of different additive concentrations on the lubricating properties of base oil. Findings The mean friction coefficient of PAO-3, PAO-20 and NPE-2 reduced by 32.8%, 10.1% and 11.4% when the adding concentration of CNPs-OA was 1.5, 2.0 and 0.5 Wt.%, respectively. Generally, The CNPs-OA exhibited the best friction-reducing and anti-wear performance in PAO-3. Originality/value The agglomeration phenomenon of carbon nanoparticles as lubricating additive was improved by surface modification, and the lubricating effect of carbon nanoparticles in three synthetic aviation lubricating base oils was compared.

Study on the Surface Texture-Microparticles Synergistic Lubrication Mechanism of Artificial Joint

Abstract After total joint replacement surgery, frequent injection of lubricating substances is required due to lubrication failure caused by the absorption of lubricants by the human body, which will cause serious physiological and psychological burdens on patients. In this study, with the help of surface texture aggregation of particles, gelatin microgel particles with a diameter of about 4 μm were used as lubricating substances to achieve aggregation in the texture, thus improving the friction environment under low-concentration lubricants. The study found that the rectangular cross-sectional texture demonstrated the most effective anti-friction properties, resulting in a 26% reduction in friction coefficient compared to non-textured surfaces. Additionally, utilizing comsol for particle flow simulation, researchers observed the motion behavior of particles within the texture and clarified the mechanism of particle aggregation and the improvement of lubrication on the surface. This article confirms the beneficial effects of combining surface texture and particles on lubrication, thus providing valuable insight for improving lubrication in dilute particle solutions.

Enhancing Water Lubrication in UHMWPE Using Mesoporous Polydopamine Nanoparticles: A Strategy to Mitigate Frictional Vibration.

Establishing a persistent lubrication mechanism and a durable tribo-film on contact surfaces is identified as crucial for improving the tribology and vibration characteristics of polymer materials under water-lubricated conditions. This study focuses on enhancing tribological performance and reducing frictional vibrations in ultrahigh molecular weight polyethylene (UHMWPE) through the incorporation of mesoporous polydopamine (MPDA) nanoparticles. In the experiments, MPDA nanoparticles were synthesized and blended with UHMWPE to create UHMWPE/MPDA composites. The interactions between these composites and zirconia (ZrO2) ceramic balls under water lubrication were examined. The results show that when the MPDA content of the composite is 1.5 wt %, the coefficient of friction and wear rate are reduced by 40% and 52% compared with those of pure UHMWPE, respectively. This notable enhancement helped to mitigate friction-induced vibrations, particularly those caused by intermittent sticking and slipping motions. MPDA nanoparticles were shown to act as reservoirs for water, releasing and replenishing water based on the loading conditions, which sustained continuous water-based lubrication at the composite surfaces. Additionally, the surface deformation behavior of the composite material is significantly weakened, which provides a more stable friction surface. This work introduces a novel approach to enhance the interface stability of polymers in water-lubricated environments, offering guidance for developing advanced materials and reducing friction and wear in engineering applications.

Combining in-situ quadrupole mass spectrometer analyses: Study on the structure–activity relationship and lubrication mechanisms of ammonium phosphate ionic liquids

Since the lubrication performances of ionic liquids are closely linked to their unique structures, four protic ionic liquids (PILs), [N44HH][DEHP], [N444H][DEHP], [N448H][DEHP] and [N4412H][DEHP], are designed to investigate the effect of cationic structures on the lubrication behaviors and lubrication mechanisms. Vacuum tribological tests were carried out to minimize the impact of the atmospheric environment. The structure–activity relationships and lubrication mechanisms of PILs were emphatically examined by in-situ quadrupole mass spectrometer (Q-MS) and XPS analyses. Results demonstrated that all four PILs exhibited outstanding lubrication performance under a vacuum condition. Unusually, extended alkyl chain cationic structures resulted in a changed lubrication mechanism, leading to a slight decrease in performance. In-situ Q-MS analyses and XPS further revealed that the length of the alkyl chain in cations influenced the strength of intermolecular forces in PILs, leading to changes in their lubrication performance and mechanisms.

Enhanced creaminess of plant-based milk via enrichment of papain hydrolyzed oleosomes

There is an increased consumer demand for plant-based milk in substituting dairy milk due to the ethical, health concerns and environmentally-friendly choice. However, perceived creaminess as dominant attributes present a big challenge in consumer acceptance for those milk alternatives. In this study, we developed a novel and easily scalable strategy to enhance the creaminess of soy milk via enrichment of oleosomes. The soybean oleosome creams were extracted and hydrolyzed with papain, resulting in formation of oil droplets with more phospholipid and less protein at the surface, which significantly reduce friction coefficient in the presence of saliva (from 0.15 to 0.03 at a speed around 50 mm/s). Moreover, blending papain-hydrolyzed oleosome creams with raw soy milk enables the creation of a plant-based milk that matches the nutritional profile, lubrication properties, and creaminess of full-fat dairy milk. QCM-D and passive microrheology were employed to characterize hydration of oleosomes into the mucin layer and relevant viscosity change, suggesting that papain hydrolyzed oleosome might decrease friction coefficient via hydration lubrication mechanism. This approach could be applied to enhance the creaminess mouthfeel and nutritional profile of plant-based milk.

Study on the Effectiveness of Okra as an Environmentally Friendly and Economical Lubricant for Drilling Fluid

With the gradual improvement and implementation of unconventional wells drilling and environmental regulations, there is an urgent need for high-performance and more environmentally friendly lubricants for water-based drilling fluids (WD). Developing green oilfield chemicals from natural products is a shortcut. In this work, Abelmoschus esculentus (L.) Moench/okra has been studied as the lubricant in WD. The green drilling fluid lubricant developed demonstrates excellent lubrication performance, as well as good filtration loss reduction and inhibition of bentonite hydration expansion. The results show that with the addition of 2.5% okra slurry to water-based drilling fluid, the coefficient of friction decreased by 51.68%, the apparent viscosity (AV) increased by 51.32%, the plastic viscosity (PV) increased by 42.99%, and the fluid loss decreased by 39.88%. Moreover, through TGA, SEM, FT-IR, particle distribution tests, and contact angle tests, the lubrication mechanism of okra slurry was discussed. Finally, the economic feasibility of using okra as an environmentally friendly lubricant for drilling fluids was analyzed. This work combines agricultural products with industrial production, which not only solves industrial problems but also enhances the added value of agricultural products, providing a reference for the coordinated development of industry and agriculture.

Recent Advances in Biomimetic Related Lubrication

Friction is ubiquitous in industry and daily life, which not only leads to the wear and tear of equipment and machinery, but also causes a lot of energy waste. Friction is one of the significant factors leading to energy loss in mechanical systems. Therefore, it is essential to minimize friction losses. Creatures in nature have evolved various surfaces with different tribological characteristics to adapt to the environment. By studying, understanding, and summarizing the friction and lubrication regulation phenomena of typical surfaces in nature, various bionic friction regulation theories and methods are obtained to guide the development of new lubrication materials and lubrication systems. This article primarily discusses the study of lubrication mechanisms through biomimetic design, which is mainly divided into chemical approaches, structural strategies, and chemical–structural coupling approaches. From the chemical point of view, this paper mainly summarizes joint lubrication and engineering lubrication in biomedicine, with inspiration from lotus leaves, fish skin, and snake skin, each with unique antifriction structures which are famous for their super hydrophobicity in nature. Finally, chemical–structural coupling simulates the lubrication mechanism of natural organisms from the joint action of biological structures and chemical substances, and is applied to coating design, so as to reduce the friction and wear on coating surfaces, improve the durability and anti-pollution ability of coatings, significantly improve the tribological performance of mechanical systems, promote scientific innovation, and promote energy conservation, emission reduction, and sustainable development.

Shrouding Gas Plasma Deposition Technique for Developing Low-Friction, Wear-Resistant WS2-Zn Thin Films on Unfilled PEEK: The Relationship Between Process and Coating Properties

In this study, tungsten disulfide–zinc (WS2-Zn) composite films were generated on polyether ether ketone (PEEK) disks by an atmospheric pressure plasma jet (APPJ) equipped with a shrouding attachment. The friction and wear properties of the WS2-Zn coatings were intensively investigated by using a rotational ball-on-disk setup under dry sliding and ambient room conditions. In order to gain more information about the lubrication mechanism, the coating areas as deposited and the worn areas (i.e., in the wear track) were analyzed with a scanning electron microscope (SEM) with regard to their chemical composition in depth by energy-dispersive X-ray spectroscopy (EDS). X-ray photoelectron spectroscopy (XPS) was conducted to obtain precise chemical information from the surface. The results indicated that WS2-Zn coatings significantly improved the tribological properties, exhibiting a coefficient of friction (COF) of <0.2. However, the tribological performance of the coatings is strongly dependent on the plasma process settings (i.e., plasma current, dwell time of the powder particles in the plasma jet), which were tuned to reduce the oxidation by-products of WS2 to a minimum. The COF values achieved of the dry lubricant films were significantly reduced in contrast to the uncoated PEEK by a factor of four.

Lubrication mechanism analysis of textures in journal bearings using CFD simulations

Purpose This paper aims to study the lubrication mechanism of textured journal bearings. Design/methodology/approach CFD models for textured journal bearings are established. The effect of texture coverage on the pressure distribution is studied to find the proper texture distribution. To enhance the local load-carrying capacity at textures, the micro-hydrodynamic pressure and microflow at different texture depth ratios are captured. The interaction between the texture-induced microflow and the bearing lubrication film is analyzed from the microflow perspective. Findings The bearing performance is on the one hand enhanced by the micro-hydrodynamic pressure generated by textures. On the other hand, the main bearing land and maximum pressure can be interfered by textures, leading to the reduction of load-carrying capacity. To minimize the interference effect, textures are suggested to distribute downstream of the minimum film thickness location. As the lubrication film thickness increases, the corresponding optimum texture depth ratio rises. The vortices influence the local flow rate through the lubrication film at textures and further affect the micro-hydrodynamic pressure and local load-carrying capacity. The texture depth ratio, at which vortices begin to occur, generates the maximum micro-hydrodynamic pressure. Originality/value The proper texture distribution is introduced, which is capable to generate the micro-hydrodynamic pressure without interfering with the primary load-carrying capacity of the bearing. The microflow effect is found to considerably influence the local load-carrying capacity at textures. The necessity of sub-regional optimization in textured journal bearings is pointed out. This study provides the fundamental reference for the design and optimization of textured journal bearings.

Specific Degradation of the Mucin Domain of Lubricin in Synovial Fluid Impairs Cartilage Lubrication.

Progressive cartilage degradation, synovial inflammation, and joint lubrication dysfunction are key markers of osteoarthritis. The composition of synovial fluid (SF) is altered in OA, with changes to both hyaluronic acid and lubricin, the primary lubricating molecules in SF. Lubricin's distinct bottlebrush mucin domain has been speculated to contribute to its lubricating ability, but the relationship between its structure and mechanical function in SF is not well understood. Here, we demonstrate the application of a novel mucinase (StcE) to selectively degrade lubricin's mucin domain in SF to measure its impact on joint lubrication and friction. Notably, StcE effectively degraded the lubricating ability of SF in a dose-dependent manner starting at nanogram concentrations (1-3.2 ng/mL). Further, the highest StcE doses effectively degraded lubrication to levels on par with trypsin, suggesting that cleavage at the mucin domain of lubricin is sufficient to completely inhibit the lubrication mechanism of the collective protein component in SF. These findings demonstrate the value of mucin-specific experimental approaches to characterize the lubricating properties of SF and reveal key trends in joint lubrication that help us better understand cartilage function in lubrication-deficient joints.

Study on Atomization Mechanism of Oil Injection Lubrication for Rolling Bearing Based on Stratified Method

The atomization mechanism of lubrication fluid in rolling bearings under high-speed airflow between the rings was investigated. A simulation model of gas–liquid two-phase flow in angular contact ball bearings was developed, and the jet lubrication process between the bearing rings was simulated using FLUENT computational fluid dynamics software (Ansys 19.2). The complex motion boundary conditions of the rolling elements were addressed through a layered approach. We can obtain more accurate boundary layer flow field changes and statistics of the diameter of oil particles in lubricating oil atomization, which lays the foundation for analyzing the law of influence on lubricating oil atomization. The results show that as the number of boundary layer layers increases, the influence of the boundary layer flow field on the lubricating oil is more obvious. The oil particle size is excessively flat, and the concentration of large particles of oil appears to decrease. As the speed increases, the amount of oil in the cavity decreases, but the oil droplets are also fragmented, which intensifies the atomization and reduces the particle diameter. This reduces the Sauter Mean Diameter (SMD), which is not conducive to the lubrication of the bearing. Under different injection pressures, when the injection pressure is large, it is beneficial to the lubrication of the bearing.

Fabrication of Vanadium Oxide-encapsulated Hybrid Carbon Nanospheres for Enhanced Tribological Performance.

A new sulfur-containing carbon nanospheres encapsulated with vanadium oxide (V@SCN) is synthesized through a one-pot oxidation polymerization and then carbonization method. The prepared V@SCNs exhibit good dispersibility as a lubricant additive, which is owing to the inherited lipophilic organic functional groups in the sulfur-containing carbon shell derived from the carbonization of polythiophene. The agglomeration and precipitation of metals in the base oil are also avoided through the encapsulation of lipophilic carbon shells. The stress and thermal simulation results show that the vanadium oxide core bestows upon the carbon nanospheres enhanced load resistance and superior thermal conductivity, which contributes to their excellent tribological properties. Introducing 0.04M-V@SCN to the base oil leads to favorable tribological characteristics, such as a fourfold rise in extreme pressure capacity from 250 to 1050N, a reduction in friction coefficient from 0.2 to ≈0.1, and a substantial decrease in wear by 90.2%. The lubrication mechanism of V@SCNs as lubricant additive involves the formation of a robust protective film on the friction pair, which is formed via complex physical and chemical reactions with the friction pair during friction.

Meniscal scaffolds based on self-healable elastomer-hydrogel composites with biomimetic structure and tribological properties for repairing meniscal injuries

Meniscal injuries are increasing dramatically with the aging of the population and the prevalence of sports. Tissue engineering technology is the most promising method for the treatment of meniscal injuries, but the preparation of long-term and durable meniscal scaffolds with mechanical and tribological properties like natural articular cartilage remains a great challenge. Here, inspired by the structure and lubrication mechanism of the meniscus, a durable meniscus scaffold with bionic 3D structure, self-lubrication, and intelligent drug release function is prepared. An elastomer-hydrogel composite consisting of a direct ink writing (DIW) printed elastomer skeleton and a hydrogel matrix is prepared for the meniscus scaffold. The bionic 3D structure of the scaffolds is realized by combining computer-aided structural design and 3D printing technology. The self-healing ability obtained by incorporating dynamic covalent bonds, and the robust interface achieved by co-curing of the elastomer and hydrogel resins, ensure the stability and durability of the composite meniscal scaffolds. Taking advantage of the coexistence of aqueous and oily phases in the emulsion-type hydrogel resin, a hydrophobic phospholipid is loaded into the hydrogel, and achieves excellent boundary lubrication of the composite through its fiction-response release and self-assembly. Moreover, the meniscus scaffolds enable intelligent drug release to adapt to the physiological characteristics during inflammation. In vivo tests in rabbit models validate the protective effect of the scaffold on cartilage. These methods and concepts provide a solid foundation for the preparation of bionic tissue scaffolds.

Effect of nano-Cu-loaded graphene fillers on tribological properties of PTFE based composite coatings

The Polytetrafluoroethylene(PTFE)-based composite coating has been widely used in the tribology field due to the high strength of graphene(GNS) and the self-lubricating property of PTFE. However, the weak interfacial bonding between GNS and PTFE inhibits the tribological performance of PTFE-based composite coatings. In this study, the composite coating is in situ fabricated by loading Cu nanoparticles on the GNS surface, and the microstructure, bonding, friction, and wear properties of the composite coating were investigated. The results showed that the interfacial bond strength, friction, and wear properties of Cu@GNS-PTFE coating are higher than those of pure PTFE and GNS-PTFE coating. Compared with the PTFE coating, the Cu@GNS-PTFE coating with the optimal ratio(5%) can increase the bond strength by 24.6% and reduce the wear rate by 42.2%. The lubrication mechanism of the Cu@GNS-PTFE coating is the Cu nanoparticle can increase the interfacial bonding property of GNS and PTFE from both mechanical interlocking and chemical activity, which can promote the synergistic lubrication of GNS and PTFE, and provide a theoretical basis for the further application of PTFE and GNS.

An investigation on tribological behavior of TC bearing materials: Effect of nano-SiO2 concentrations under different loads in the drilling fluid environment

Both Nano-SiO2 (Silicon dioxide nanoparticles) additive concentration and axial load have profound effects on the friction and wear of Tungsten Carbide bearings in the drilling fluid environment. However, the coordinated role of them remains unknown. In this work, the effects of Nano-SiO2 concentrations and axial loads on the tribological behavior of bearing materials were investigated simultaneously. Results show that the water-based drilling fluid containing Nano-SiO2 exhibits more excellent lubrication properties under 200 N as compared with 70 N, and the optimal concentration of Nano-SiO2 additive is 1.0 wt% under all loads. High axial loads are conducive to improve the lubrication performance, and the lubrication mechanisms of Nano-SiO2 under different loads in water-based drilling fluid are the multitudinousness of synergistic effects, including rolling bearing, polishing, shielding, and self-healing effect, which all manifested there is an remarkable load dependence of Nano-SiO2 particles.