Lubrication Mechanism Research Articles

Novel Polymer Gel Lubricant Functionalized with a Phosphate Anion for Friction Reduction and Film Thickness Enhancement in Multiple Lubrication Conditions.

In this study, a supramolecular polymer gelator functionalized with a phosphate anion, PMUS-P, has been successfully synthesized through radical polymerization, and its physicochemical, rheological properties and tribological performance were carefully evaluated as a gel lubricant formed through non-covalent self-assembly in 500SN base oil. The results showed that the gel has a dense network structure, providing excellent stability and mechanical strength. Additionally, the PMUS-P gel exhibits good shear-thinning behavior and excellent creep recovery, effectively avoiding the volatility of lubricants. Under a steel-steel contact, the PMUS-P gel showed excellent tribological performance in long-term wear tests and a high-load, high-frequency, or high-temperature condition. For instance, in long wear tests, the 15 wt % PMUS-P gel showed a 44.90% reduction in average coefficient of friction (COF) compared to 500SN base oil, along with an 88.05% decrease in wear. The lubrication mechanism study revealed that the chemical reactive film formed by friction played a key role in reducing friction and wear, preventing the friction pairs from direct contact. In terms of film-forming properties, the PMUS-P gel demonstrates superior lubrication performance in comparison to 500SN base oil, achieving higher film thickness. Given these advantages, the PMUS-P gel has significant potential for prolonging machinery service life and reducing operational energy consumption, promising to become a new high-performance lubricant.

A motion-responsive injectable lubricative hydrogel for efficient Achilles tendon adhesion prevention.

Achilles tendon is a motor organ that is prone to tissue adhesion during its repair process after rupture. Therefore, developing motion-responsive and anti-adhesive biomaterials is an important need for the repair of Achilles tendon rupture. Here, we report an injectable lubricative hydrogel (ILH) based on hydration lubrication mechanism, which is also motion-responsive based on sol-gel reversible transmission. The lubrication performance is achieved by zwitterionic polymers as we previously proved, and the sol-gel reversible transmission is enabled by dynamic disulfide bonds. Firstly, ILH was proved to be successfully prepared and lubricated as well as sol-gel reversible via FTIR characterization, rheological measurement and tribological tests. Then, in vitro cell experiments and coagulation tests demonstrated the optimal cytocompatibility and hemocompatibility of ILH. To evaluate the potential of ILH's biofunction in vivo, SD rats' Achilles tendon rupture & repair model was established. The animal experiments' results showed that ILH significantly prevented tendon adhesion and thus promote tendon healing by inhibiting TGFβ1-Smad2/3 pathway. We believe this work will open a new horizon for tendon adhesion-free repair.

Molecular Dynamics Simulation of the Hydration Lubrication Mechanism of CS-MPC/CS-ChS NPs.

Osteoarthritis (OA) remains a significant clinical challenge, with current treatments like sodium hyaluronate injections offering limited efficacy due to suboptimal lubrication and rapid degradation. In this study, we explored an advanced solution to these issues by investigating the colubrication mechanism of a composite biolubricant consisting of 2-methacryloyloxyethyl phosphorylcholine-modified chitosan (CS-MPC) and chondroitin sulfate-modified chitosan nanoparticles (CS-ChS NPs) using molecular dynamics (MD) simulations. Results show that the composite lubricant outperforms individual CS-MPC or CS-ChS NPs, exhibiting a lower coefficient of friction (COF) and a superior load-bearing capacity. The CS-MPC/CS-ChS NP system maintains a consistent compression ratio of -0.5% under different external pressures and exhibited a low coefficient of friction (COF) of 0.041 across varying shear velocities. The sulfate groups on CS-ChS NPs interact with CS-MPC chains, stabilizing the system through electrostatic interactions and enabling the effective dispersion of normal stress, thereby protecting the substrate surface from wear. This enhanced performance is attributed to the formation of a multilayered hydration shell around the lubricant molecules. The hydration shells provide superior lubrication, contributing to the system's robustness under varying loads. These findings offer critical insights into designing high-performance biolubricants for joint protection, presenting a promising avenue for future OA treatments.

Fabrication of AFM-Compatible Hydrogel Probe to Achieve Hydration Superlubrication in Salt Solutions.

Hydrogels demonstrate effective lubricating properties, but the underlying mechanisms at the nanoscale remain elucidated. In this study, a novel strategy is proposed by fabricating the hydrogel probes compatible with atomic force microscopy (AFM) to establish a superlubrication system based on the hydration interactions. The probe is made of polyethylene glycol diacrylate (PEGDA)-based hydrogel microspheres, which can achieve an extremely low friction coefficient of 0.0014 when sliding on the mica surface in NaCl solution. The friction coefficients in salt solutions sequence μ(NaCl) <0.01 < μ(KCl) < μ(LiCl), which contradicts the sequence based on the ion hydration capacity (K+ < Na+ < Li+), suggesting that the hydrogel-based lubrication systems are governed by the interplay between ion hydration lubrication and ions-polymer interactions simultaneously. The observed superlubrication in NaCl solution is ascribed to the superior hydration capacity of Na+ ions, which forms a stable and smooth hydration layer within the contact zone. This work provides new avenues for AFM-based hydrogel studies, and also significantly advances the comprehension of hydrogel lubrication mechanisms at the nanoscale.

Friction Reduction and Antiwear Mechanisms of Cerium Sulfide Nanosheets under Different Sliding Conditions.

With the rapid development of modern industry, traditional lubricants often require a variety of additives to be used in conjunction with each other, which not only increases the cost but also causes a waste of resources. Therefore, the development of a lubricant additive with both a dyeing function and an antiwear and friction reduction performance can more effectively meet the industrial needs. Cerium sulfide (Ce2S3), with its excellent photostability, weather resistance, thermal stability, and nontoxicity, shows great potential as an environmentally friendly pigment. However, traditional methods for synthesizing Ce2S3 are typically hindered by high-temperature requirements and potential toxicity issues, which limits the broad application of Ce2S3 in lubricants. To overcome these limitations, this study employed a liquid-phase method under mild conditions to synthesize oleylamine-modified, wrinkle-free Ce2S3 nanosheets (OA-Ce2S3 NSs). The antiwear and friction-reducing properties of OA-Ce2S3 NSs in poly alpha-olefin-6 base oils were evaluated under various friction conditions with a four-ball tribometer. Experimental results indicate that OA-Ce2S3 NSs significantly enhance the friction-reducing and antiwear performance of lubricants by forming a physical adsorption film and an ultra thick tribochemical reaction film (with a typical thickness of 350 nm and a maximum thickness of up to 700 nm) on the friction surface. Furthermore, the study elucidates the lubrication mechanism of OA-Ce2S3 NSs and proposes their sliding mechanism on friction surfaces. This research highlights the potential of Ce2S3 nanosheets as lubricant additives and provides future directions for optimizing their synthesis and multifunctional applications, offering new insights into the field of lubrication science.

Tribological performance of carbon nanospheres as lubricant additives: insights from molecular dynamics simulation and experimental analysis

Abstract To investigate the lubrication mechanism of carbon nanospheres and compare their tribological performance with carbon powder, this study presented a comprehensive analysis of their potential as lubricant additives through both experimental testing and molecular dynamics simulations. Carbon nanospheres were synthesized using the hydrothermal method. Extensive comparisons were conducted between carbon powder and carbon nanospheres, focusing on material characterization, dispersion stability, antifriction performance, and antiwear capability. Findings revealed that carbon nanospheres outperformed carbon powder as lubricant additives in PAO 10 owing to their smaller particle size and spherical shape. Specifically, at a concentration of 1wt%, a load of 50 N, a disk speed of 10 rpm, and a temperature of 25 °C, the addition of carbon nanospheres reduced the friction coefficient by 34% and wear volume by 35%. The improved tribological performance was linked to the ability of carbon nanospheres to fill the pits, improving the interface smoothness. Molecular dynamics simulation of carbon nanospheres effectively reflected substrate roughness in the bulk region and further confirmed that this filling effects increased the lubricant's load-bearing capacity, which contributed to the reduction of friction and wear. This study provided significant insights into the development of innovative high-performance lubricant additives for oil-based lubrication in metal friction pairs.

The influence of a comb-like polymer functionalized phosphate ionic liquid as a lubricant additive on micropitting

In this study, a comb-like polymer functionalized phosphate ionic liquid was synthesized and tested for its effectiveness in reducing friction and wear, as well as its capability to prevent micropitting in PAO base oil using SRV and MPR. It outperforms commercially available phosphate ionic liquids. The wear surface characteristics were analyzed using optical and electron microscopy, and changes in compound structure on the wear surface were studied using XPS spectroscopy. Through a combination of experimental observations and theoretical analysis, it is suggested that the lubrication mechanism is attributed to a synergistic effect between a “soft film” containing comb-like polymers formed through the adsorption of the ionic liquid, and a tribofilm consisting of phosphate compounds and a nitrogen-containing organic matrix.

Artificial Intelligence and Machine Learning in Tribology: Selected Case Studies and Overall Potential

Artificial intelligence (AI) and machine learning (ML) have been the subjects of increased interest in recent years due to their benefits across several fields. One sector that can benefit from these tools is the tribology industry, with an emphasis on friction and wear prediction. This industry hopes to train and utilize AI algorithms to classify equipment life status and forecast component failure, mainly using supervised and unsupervised learning approaches. This article examines some of the methods that have been used to accomplish this, such as condition monitoring for predictions in material selection, lubrication performance, and lubricant formulation. Furthermore, AI and ML can support the determination of tribological characteristics of engineering systems, allowing for a better fundamental understanding of friction, wear, and lubrication mechanisms. Moreover, the study also finds that the continued use of AI and ML requires access to findable, accessible, interoperable, and reusable data to ensure the integrity of the prediction tools. The advances of AI and ML methods in tribology show considerable promise, providing more accurate and extensible predictions than traditional approaches.

Advanced Solid Lubrication with COK-47: Mechanistic Insights on the Role of Water and Performance Evaluation.

Metal-organic framework (MOF) nanoparticles have attracted widespread attention as lubrication additives due to their tunable structures and surface effects. However, their solid lubrication properties have been rarely explored. This work introduces the positive role of moisture in solid lubrication in the case of a newly described Ti-based MOF (COK-47) powder. COK-47 achieves an 8.5-fold friction reduction compared to AISI 304 steel-on-steel sliding under room air. In addition, COK-47 maintains a similarly low coefficient of friction (0.1-0.2) on various counterbodies, including Al2O3, ZrO2, SiC, and Si3N4. Notably, compared to other widely studied MOFs (ZIF-8, ZIF-67) and 2D materials powder (MXene, TMD, rGO), COK-47 exhibits the lowest friction (≈0.1) under the same experimental settings. Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, scanning electron microscope, and transmission electron microscopy indicate that the tribofilm is an amorphous film obtained by hydrolysis of COK-47 in the air with moisture. Density functional theory further confirms that water catalyzes the decomposition of COK-47, a crucial step in forming the tribofilm.This study demonstrates the idea of utilizing MOF and water-assisted lubrication mechanisms. It provides new insights into MOF applications in tribology and highlights interdisciplinary contributions of mechanical engineering and chemistry.

High-temperature tribological characteristics and lubrication mechanisms of NiCrAlY-MoO3/CoO composite coatings: An experimental and DFT computation study

High-temperature tribological characteristics and lubrication mechanisms of NiCrAlY-MoO3/CoO composite coatings: An experimental and DFT computation study

Graphene Mitigates Nanoscale Tribochemical Wear of Silica Glass in Water

AbstractDespite the ubiquitous use of glasses, their simultaneous susceptibility toward scratch‐induced defects and atmospheric hydration deteriorates their mechanical and chemical durability. Here, it is demonstrated that the deposition of a few‐layer graphene provides unprecedented wear resistance to silica glass in aqueous conditions. To this extent, nanoscale scratch tests are carried out on graphene‐glass surfaces via contact‐mode atomic force microscopy with chemically inert and reactive tips. It is observed that the graphene‐glass exhibits up to ≈98% friction reduction and no discernable damage or material loss. This observation is in stark contrast to the behavior of bare silica glass which suffers severe tribochemical wear at equivalent contact conditions with even milder stresses. Further, through reactive molecular simulations, it is demonstrated that parallel mechanisms of lubrication and chemical passivity contribute to the enhanced damage resistance of graphene‐glass surfaces against any countersurface chemistry. Altogether, the present study provides an impetus toward physically and chemically durable glass coatings exploiting the functionalities of two‐dimensional materials.

Multi‐Dimensional Nano‐Additives for Their Superlubricity: Tribological Behaviors and Lubrication Mechanisms

AbstractThe significant contribution of super lubrication is to achieve ultra‐low friction in the friction pair, improving the wear resistance of the contact surface and thus achieving energy savings and environmental protection. Despite numerous experimental studies exploring the mechanism contributing to superlubrication, there is a relative scarcity of overall generalizations regarding the recent development of 0D–3D nanomaterials in superlubrication. Therefore, this paper systematically reviews the latest research progress on nanomaterials for achieving ultra‐low friction and wear in solid/liquid lubrication systems focusing on the structural characteristics of 0D‐3D nanomaterials. The important role of nanomaterial dispersion in the superlubrication steady state is discussed in detail, and recommendations are made for the key challenges of future engineering‐scale macroscopic superlubrication applications.

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.

Analysis of the Film-Forming Characteristics of Water Lubrication Assisted by Small Amount of Secondary Lubricating Oil

Abstract This study investigates the film formation mechanism of lubrication using a small quantity of lubricating medium in a water environment. A roller-on-disc test rig combined with a fluorescent technique is employed to directly measure and observe the film formation behavior when a small amount of lubricating medium is introduced into the water. Additionally, a surface-modified disc is used to examine the impact of wettability gradients on the film-forming capability of the lubricating medium. The results indicate that the film thickness between the roller and the disc increases with the injection of two types of lubricating oils into the water at varying disc speeds, both for the original and modified discs. During the 10-second oil supply period, the spreading behavior of the lubricating oil on the lubricating track influences the film thickness stability. Furthermore, the surface-modified disc demonstrates an enhanced film thickness compared to the original disc, and viscosity becomes a key factor limiting the film-forming capability of the lubricating oil as the disc speed increases for both disc types. This research offers valuable insights for the design of new water-lubricated bearings.

Zr-MOFs (UIO-66-NH2)@Fluorinated Graphene for Developing Highly Antiwear, Friction-Reduction Lubricating Additives.

Fluorinated graphene (FG) among numerous two-dimensional materials has enormous potential in improving antifriction properties. However, they being susceptible to thermal oxidation and prone to wear hinder practical applications. Herein, UIO-66-NH2 (Zr-MOF) enjoying good chemical and thermal stabilities was assembled on the surface of FG nanosheets under covalent bonds and van der Waals forces. The Zr-MOF@FG composite was successfully synthesized and used as a lubricant additive. It can be seen that Zr-MOF@FG composites offer a synergistic lubricant mechanism at the friction interface. Moreover, due to the adsorption and purification performance of Zr-MOF, the obtained Zr-MOF@FG composite adsorbs the abrasive rust during the friction process, thereby realizing the purification of the lubricant. These findings suggest that Zr-MOF@FG shows tremendous potential as a lubricant additive.

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

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.