Superior Lubrication Properties Research Articles

Mechanically durable plant-based composite surface towards enhanced antifouling properties

The biofouling adhering to underwater facilities has a negative impact on the environment, energy, and economic development. However, conventional anti-adhesion organic silicon and organic fluorine materials often have poor adhesion properties and mechanical stability when combined with substrates. This work presents a novel strategy for preparing composite antifouling coatings that low surface energy plant-based carnauba wax (CW) covering through rough substrates and chemically bond with flexible polydimethylsiloxane (PDMS) oligomers or polymers. The CW coating adheres strongly to the substrate owing to the mobility of the liquated CW, which flows into the micro-nano structure of the substrate and solidifies on the solid surface. The polymerization reaction of (PDMS) oligomers compounded the coating, thereby creating a composite coating with superior lubricating and antifouling properties. This distinctive bonding process imbued the coating with exceptional characteristics, including remarkable mechanical stability in destructive tests as well as an impressive ability to repel fouling, such as protein attachment, bacterial adhesion, diatom deposition, and biofilm formation. This work systematically investigated the impact of the composition and structure of composite materials on their mechanical stability and resistance to fouling, and developed high-performance antifouling coatings in the real world.

Performance evaluation of cold plasma and h-BN nano-lubricant multi-field coupling assisted micro-milling of aluminum alloy 6061-T651

Micro-milling has been employed in various fields due to its efficiency, flexibility, material, and structural versatility in the machining of small and high-quality parts. However, when micro-milling highly plastic aluminum alloys, it is difficult to produce a smooth surface due to the easy sticking of tools. To solve this problem, a multi-energy field coupling method of adding nano-lubricant to the micro-milling area by minimum quantity lubrication (MQL) and modifying the aluminum alloy by cold plasma (CP) was introduced. In this paper, the experiments of CP and h-BN nano-lubricant minimum quantity lubrication (NMQL) multi-field coupling assisted (CPNMQL) micro-milling of aluminum alloy 6061-T65 were carried out to analyze 3D surface roughness (Sa), tool texture, milling forces (Fx and Fy), and surface morphology. The results revealed that the CP could increase the surface microhardness and improve material removal rate; Cottonseed oil with h-BN nanoparticles exhibited superior lubricating properties; The milling forces Fx and Fy were significantly reduced; Sa (0.029 µm) under CPNMQL condition decreased by 60 %, 72.1 %, 27.5 %, and 53.2 % comparing to dry (0.104 µm), NMQL (0.04 µm), and CP (0.062 µm) conditions. In addition, the smallest and most uniform tool mark texture height and depth of 0.038 µm was obtained under CPNMQL condition, a 76.3 % reduction over dry condition.

Tough, Slippery, and Low-Permeability Multilayer Hydrogels Modified by Anisotropic Fiber Membrane for Soft Tissue Replacement.

Hydrogels with sustained lubrication, high load-bearing capacity, and wear resistance are essential for applications in soft tissue replacements and soft material devices. Traditional tough or lubricious hydrogels fail to balance the lubrication and load-bearing functions. Inspired by the gradient-ordered multilayer structures of natural tissues (such as cartilage and ligaments), a tough, smooth, low-permeability, and low-friction anisotropic layered electrospun fiber membrane-reinforced hydrogel was developed using electrospinning and annealing recrystallization. This hydrogel features a stratified porous network structure of varying sizes with tightly bonded interfaces, achieving an interfacial bonding toughness of 1.6 × 103 J/m2. The anisotropic fiber membranes, mimicking the orderly fiber structures within soft tissues, significantly enhance the mechanical properties of the hydrogel with a fracture strength of 20.95 MPa, a Young's modulus of 29.64 MPa, and a tear toughness of 37.94 kJ/m2 and reduce its permeability coefficient (6.1 × 10-17 m4 N-1 s-1). Meanwhile, the hydrogel demonstrates excellent solid-liquid phase load-bearing characteristics, which can markedly improve the tribological performance. Under a contact load of 4.1 MPa, the anisotropic fiber membrane-reinforced hydrogel achieves a friction coefficient of 0.036, a 219% reduction compared with pure hydrogels. Thus, the superior load-bearing and lubricating properties of this layered hydrogel underscore its potential applications in soft tissue replacements, medical implants, and other biomedical devices.

Atomistic understanding of the interlayer friction of graphullerene

Graphullerene, an emerging two-dimensional carbon allotrope derived from C60, is endowed with distinctive mechanical and thermal characteristics, positioning it as a potential candidate with superior lubricating properties akin to graphene and C60. This research delves into the interlayer frictional behavior of graphullerene through molecular dynamics simulations, meticulously examining the impact of sliding velocity, normal load, flake orientation, and temperature. The findings reveal a stick-slip mode of friction with an exponential increase in friction force as sliding velocity increases. Additionally, the study captures the formation of puckering at the slider's forefront, which undergoes ballistic motion propelled by the slider's momentum. Notably, at higher velocities, a distinctive "stone skipping" effect is observed, with the graphullerene flake intermittently detaching from the substrate.

A bioinspired hard-soft composites with strong interfacial bonding, high load-bearing and low friction for osteochondral repair

The development of osteochondral composites that simultaneously exhibit superior load-bearing performance and lubrication properties remains a significant challenge. In this investigation, a novel hard-soft composite material, which utilizes porous Si3N4 ceramics as a structural support and PVA-CBA (synthesis by condensation of polyvinyl alcohol and 4-formylbenzoic acid) hydrogels as a lubrication, was fabricated via impregnating the hydrogel into porous ceramics, namely Si3N4/PVA-CBA composites. It demonstrates strong interfacial bonding, comprising macro-micro scale mechanical interlocking and molecular scale chemical crosslinking. The developed material exhibits high mechanical strength (∼ 103.2 MPa and ∼ 1500 % larger than the corresponding value of porous Si3N4 ceramics), low friction and wear (∼ 0.21 under 10 N load and 10 Hz frequency), and favorable cell adhesion and proliferation. This provides an effective strategy for designing hard-soft composite material in the osteochondral repair field.

Tribological properties of pickering emulsion constructed with ZnO nanoparticles modified by magnetic surfactants

To fulfill the requirements of long-term stable lubrication and corrosion protection, conventional industrial emulsion lubricants often involve complex formulations with multiple components, posing challenges in terms of preparation, recycling, and potential environmental impact. In order to address the problems, a Pickering emulsion with a simple composition and excellent anti-corrosion properties is prepared by incorporating magnetic surfactant ((C18H37)2N+(CH3)2[CeCl4]-) modified ZnO nanoparticles as a multifunctional additive into colza oil and water. The results demonstrate that Pickering emulsions exhibit excellent stability. Moreover, their magnetic responsiveness makes them promising candidates for intelligent lubricants. Furthermore, effective recycling and sustainability are achieved through reversible emulsification and demulsification. Tribological test results reveal that the addition of modified ZnO enhances the emulsions’ anti-friction and anti-wear properties due to nanoparticle rolling and repairing effects, generation of tribofilms, and deposition of ZnO nanoparticles. We anticipate that the Pickering emulsion could find widespread applications in various sectors, including metalworking and industrial manufacturing, owing to its uncomplicated composition, environmentally friendly nature, excellent anti-corrosion capabilities, and superior lubricating properties.

Comparative study of dry high-temperature tribological performance of hydrogen-free and hydrogenated DLC films deposited by HiPIMS in DOMS mode

Solid lubricants are crucial for industries operating at temperatures beyond 300 ºC, where liquid lubricants encounter limitations. Diamond-like carbon (DLC) films, known for exceptional solid lubrication and mechanical properties, need higher thermal stability for effective use in high-temperature applications. This study focuses on developing DLC films with the required thermal stability and solid lubricating properties. Hydrogen-free and hydrogenated DLC films were deposited utilizing deep oscillation magnetron sputtering (DOMS). Thermal characterizations revealed both films surpassed 500 ºC in thermal stability, rendering them suitable for high-temperature tribological applications. However, the hydrogenated DLC film exhibited superior solid lubricating properties, achieving an ultra-low friction coefficient below 0.05 at elevated temperatures, along with enhanced wear resistance, while effectively protecting its counterpart up to 500 ºC.

Formulation and evaluation of bio-grease from the blend of chemically modified rice bran oil and Calophyllum inophyllum oil

Vegetable oils are a highly promising alternative to produce various lubricants, owing to their biodegradability and eco-friendliness. In comparison to mineral oil, these oils possess a higher flash point and viscosity index, along with superior lubricating properties. Additionally, most of the vegetable oils are easily accessible in local markets in India. However, their industrial application is limited by poor thermal and oxidative stability, which can be addressed through chemical modification, the addition of appropriate additives, or by blending these oils. Greases, characterized by their semi-solid consistency, are widely used lubricants. Most of the grease production is based on mineral oils as base oil and lithium soap as a thickener. These materials are not only non-biodegradable but also scarce and have health implications. Consequently, biodegradable grease represents an eco-friendly and healthy alternative. Grease made using vegetable oils with the required properties has the potential to bring about revolutionary changes. The present work focuses on the feasibility of using chemically modified blended rice bran oil (RBO) and Calophyllum inophyllum oil (CIO) as a bio-lubricant. The oils undergo a two-step modification process, involving a transesterification reaction followed by epoxidation. Significant improvements have been observed in the chemical properties (acid, peroxide, and iodine values) of transesterified epoxidized rice bran oil Calophyllum inophyllum oil mixture–50:50 (ETRCIO) when compared with Unmodified Rice bran oil Calophyllum inophyllum oil mixture–50:50 (RCIO). The acid value, peroxide value, and iodine value improved by 91.66%, 87.08%, and 15.78% respectively. The rheological, tribological, and chemical properties of the blended samples have been evaluated and compared to pure oils using American Society for Testing and Materials (ASTM) and Indian Standards (IS). Additionally, ETRCIO was used to develop a bio-grease, and its tribological properties were extensively analyzed. The mean coefficient of friction (COF) and wear scar diameter (WSD) of the ETRCIO grease sample improved by 10.20% and 29.32% respectively when compared with that of commercially available grease. These findings indicate that the ETRCIO bio-grease exhibits superior tribological properties in comparison to commercially available grease.

Graphite Fluoride as a Novel Solider Lubricant Additive for Ultra-High-Molecular-Weight Polyethylene Composites with Excellent Tribological Properties

The tribological properties of ultra-high-molecular-weight polyethylene (UHMW-PE) play a significant role in artificial joint materials. Graphite fluoride (GrF), a novel solid lubricant, was incorporated into ultra-high-molecular-weight polyethylene (UHMW-PE) at different concentrations via ball milling and heat pressing to prepare the GrF-UHMW-PE composites. The structure, hardness, and tribological behavior of the composites were investigated using X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectrometry, ball indentation hardness, and a reciprocating ball-on-plane friction tester, respectively. The results of FT-IR showed that hydrogen bonds (C-F···H-C) could be formed between GrF and UHMW-PE. The hardness of the composites was significantly enhanced by increasing the GrF concentrations. GrF in the composites displayed superior lubricant properties and the coefficient of friction (COF) of the composites was significantly decreased at lower concentrations of GrF viz. 0.1 and 0.5 wt%. The addition of GrF also significantly enhanced the anti-wear properties of the composites, which was a combined effect of lubrication as well as hardness provided by GrF. At 0.5 wt% GrF concentration, the COF and the wear rate were reduced by 34.76% and 47.72%, respectively, when compared to UHMW-PE. As the concentration of GrF increased, the wear modes of the composites transitioned from fatigue wear to abrasive wear. Our current work suggested that GrF-UHMW-PE composites could be a suitable candidate for artificial joint materials.

The Synthesis of Cu-Coated Ti2SnC Ceramic and Its Tribological Behaviors as a Lubricant Additive

Lubricant additive plays an important role in reducing the friction and wear for base oil. MAX phase ceramics may have superior advantages for additive application due to their unique nanolayered structure. In this paper, Ti2SnC ceramic is prepared by sintering the elemental mixtures at 1250 °C. In addition, Cu-coated Ti2SnC ceramic is successfully prepared using a chemical plating method for the first time. It is confirmed that the Ti2SnC ceramic has good self-catalytic activity, and a layer of stacking Cu nano-particles can be deposited on the Ti2SnC surface without pretreatment. When the Cu-coated Ti2SnC ceramic powder is doped into PAO10 base oil, the oil can exhibit excellent lubrication properties, where the friction coefficient is as low as 0.095. A layer of tribo-film can be formed during the sliding process when the Cu-coated Ti2SnC ceramic is incorporated into PAO10 base oil, which can reduce the friction coefficient. The superior lubrication properties can be attributed to the synergistic lubrication effect of Ti2SnC ceramic and Cu nano-particles.

Tribological properties of MoSx/rGO nanohybrids as additives in deep eutectic solvent

Environment-friendly and sustainable deep eutectic solvents (DESs) are considered as a new type of lubricant. Here, MoSx/rGO nanohybrids were prepared as lubricant additive to improve the tribological performance of DES. The nanohybrids exhibited excellent dispersibility in DES. Tribological tests indicated that the DES with 1.5 wt% of MoSx/rGO additive exhibited the best lubrication performance for steel tribopair by reducing friction (∼31.2%) and wear (∼88.2%) due to the synergistic effect between the MoSx/rGO nanohybrid and DES. The superior lubricating properties of DES containing nanohybrids are primarily due to the attachment of nanohybrids to the friction interface, which triggers the formation of a robust tribofilm. These findings provide new insights into enhancing the tribological performance of DES by incorporating effective additives.

Lubricating Performance of Polymer-Coated Liposomes

Dry mouth is a troublesome condition linked to lubrication failure and leads to other diseases such as fungal infections and wounds in the oral cavity. There are many commercial salivary substitutes in the market, but none with a long-lasting lubrication effect. Polymer-coated liposomes can be an interesting formulation strategy for retrieving the symptoms of dry mouth by mimicking the micelles of saliva. In the present study, polymer coated-liposomes were prepared by the conventional thin film method and subsequently coated with three different polymers with different charge densities; alginate, chitosan and hydrophobically modified ethyl hydroxyethyl cellulose (HM-EHEC). The prepared polymer-coated liposomes were studied concerning their lubricating properties using a ball-on-disc tribometer at 2 N load at 37 °C, and their flow behaviours were also measured. Solutions of the pure polymers and dispersions of the uncoated liposomes were also studied to investigate any contributions from the individual components. A commercial dry mouth product based on HEC (hydroxyethyl cellulose) and glycerol was also included. The formulations were measured as soon as possible after preparation and some of them after >4 weeks. Results demonstrated that all the positively-charged formulations (chitosan, positive liposomes and chitosan-coated liposomes) had superior lubricating properties with friction coefficients (μ < 0.1) at orally relevant speeds (50 mm/s) as compared to the neutral or negatively-charged systems. At boundary lubrication conditions (3 mm/s), the chitosan-coated liposomes obtained an even lower friction force than the individual components, thus indicating a synergistic effect between the polymer and the liposome.

Constructing tough bilayer hydrogel with excellent lubrication performance for load-bearing application

Numerous strategies have been proposed to improve the strength and stiffness of hydrogels, which significantly sacrificed water content, thereby compromising lubrication properties. Hence, it remains challenging to develop elastic and strong hydrogels with excellent lubrication properties for a wide range of applications. Inspired by the stratified structure of natural bio-tissues, the mechanically strong bilayer hydrogels comprising of soft lubricating layer and hard load-bearing layer were prepared. The top porous structure could trap water molecules to achieve low friction (COF∼0.009) under a heavily loaded condition of 5 N (contact stress∼2.5 MPa), while the bottom layer provided excellent load-bearing capacity. The bilayer hydrogel with high mechanical strength, superior lubrication and excellent wear-resistance properties has considerable potential in joint replacement and tissue scaffold.

Tribological Evaluation of Few-Layer Nitrogen-Doped Graphene as an Efficient Lubricant Additive on Engine Cylinder Liner: Experiment and Mechanism Investigation

Abstract The restricted adsorption capacity of ordinary graphene at high temperature limits its application in engine lubrication. To address this, nitrogen-doped element-modified graphene with strong adsorption and superior lubricating properties is prepared by a bottom-up chemical strategy in this study. The reciprocating tribometer is aimed at simulating the piston operating environment to determine the lubrication performance of nitrogen-doped graphene. The characterization and analysis of the wear marks are performed by means of depth-of-field microscope, scanning electron microscope, energy dispersive spectrometer, and other instruments. The experimental data demonstrate that the friction-reduction and anti-wear properties of PAO 6 base oil are enhanced by 22.4% and 56.9% (100 °C), respectively, after the addition of 0.4 wt% nitrogen-doped graphene. Besides, the abrasive and adhesive wear are significantly reduced, which are attributed to its inter-layer slip along the sliding direction and superior adsorption performance. Finally, the interfacial lubrication mechanism of lubricant protective film under high-temperature conditions is revealed.

Unraveling Large and Polyploidy Genome of the Crucifer Orychophragmus violaceus in China, a Potential Oil Crop.

The genus Orychophragmus in the Brassicaceae family includes the types with 2n = 20, 22, 24, and 48. The species O. violaceus (L.) O. E. Schulz has 2n = 24 and is widely cultivated as an ornamental plant in China. This review summarizes the research progress of its genome structure and evolution in the context of cytogenetics and genome sequencing. This species has a large genome size of ~1 Gb and longer chromosomes than those of Brassica species, which is attributable to the burst of TE insertions. Even more, one tetraploidization event from about 600-800 million years ago is elucidated to occur during its genome evolution, which is consistent with the polyploidy nature of its genome revealed by the meiotic pairing patterns. Its chromosomes are still characterized by a larger size and deeper staining than those from Brassica species in their intergeneric hybrids, which is likely related to their inherent differences between genome structures and cytology. Its genome is dissected by the development of additional alien lines, and some traits are located on individual chromosomes. Due to the abundant dihydroxy fatty acids in its seed oil with superior lubricant properties and wide environmental adaptations, this plant promises to be utilized as one new oil crop in the future.

Frictional behaviour of plant proteins in soft contacts: unveiling nanoscale mechanisms.

Despite the significance of nanotribology in the design of functional biomaterials, little is known about nanoscale friction in the presence of protein-coated soft contact surfaces. Here, we report a detailed investigation of frictional behaviour of sustainable plant proteins at the nanoscale for the first time, using deformable bio-relevant surfaces that achieve biologically relevant contact pressures. A combination of atomic force microscopy, quartz crystal microbalance with dissipation monitoring, and friction force microscopy with soft polydimethylsiloxane (PDMS, 150 kPa) surfaces was employed to elucidate the frictional properties of model plant proteins, i.e. lupine, pea, and potato proteins at the nanoscale while systematically varying the pH and ionic strength. Interactions of these plant proteins with purified mucins were also probed. We provide the much-needed direct experimental evidence that the main factor dictating the frictional properties of plant proteins is their affinity towards the surface, followed by the degree of protein film hydration. Proteins with high surface affinity, such as pea and potato protein, have better lubricating performance than lupine at the nanoscale. Other minor factors that drive lubrication are surface interactions between sliding bodies, especially at low load, whilst jamming of the contact area caused by larger protein aggregates increases friction. Novel findings reveal that interactions between plant proteins and mucins lead to superior lubricating properties, by combining high surface affinity from the plant proteins and high hydration by mucins. We anticipate that fundamental understanding gained from this work will set the stage for the design of a plethora of sustainable biomaterials and food with optimum nanolubrication performance.

MoS2 nanoflower-decorated lignin nanoparticles for superior lubricant properties.

Lignin has been, for a long time, treated as a low-value waste product. To change this scenario, high-value applications have been recently pursued, e.g., the preparation of hybrid materials with inorganic components. Although hybrid inorganic-based materials can benefit from the reactive lignin phenolic groups at the interface, often responsible for optimizing specific properties, this is still an underexplored field. Here, we present a novel and green material based on the combination of hydroxymethylated lignin nanoparticles (HLNPs) with molybdenum disulfide (MoS2) nanoflowers grown via a hydrothermal route. By bringing together the lubricant performance of MoS2 and the structural stability of biomass-based nanoparticles, a MoS2-HLNPs hybrid is presented as a bio-derived additive for superior tribological performances. While FT-IR analysis confirmed the structural stability of lignin after the hydrothermal growth of MoS2, TEM and SEM micrographs revealed a homogeneous distribution of MoS2 nanoflowers (average size of 400 nm) on the HLNPs (average size of 100 nm). Regarding the tribological tests, considering a pure oil as reference, only HLNPs as bio-derived additives led to a reduction in the wear volume of 18%. However, the hybrid of MoS2-HLNPs led to a considerably higher reduction (71%), pointing out its superior performance. These results open a new window of opportunity for a versatile and yet underexplored field that can pave the way for a new class of biobased lubricants.

Genome assembly of the Brassicaceae diploid Orychophragmus violaceus reveals complex whole-genome duplication and evolution of dihydroxy fatty acid metabolism

Orychophragmus violaceus is a Brassicaceae species widely cultivated in China, particularly as a winter cover crop in northern China because of its low-temperature tolerance and low water demand. Recently, O.violaceus has also been cultivated as a potential industrial oilseed crop because of its abundant 24-carbon dihydroxy fatty acids (diOH-FAs), which contribute to superior high-temperature lubricant properties. In this study, we performed de novo assembly of the O.violaceus genome. Whole-genome synteny analysis of the genomes of its relatives demonstrated that O.violaceus is a diploid that has undergone an extra whole-genome duplication (WGD) after the Brassicaceae-specific α-WGD event, with a basic chromosome number of x= 12. Formation of diOH-FAs is hypothesized to have occurred after the WGD event. Based on the genome and the transcriptome data from multiple stages of seed development, we predicted that OvDGAT1-1 and OvDGAT1-2 are candidate genes for the regulation of diOH-FA storage in O.violaceus seeds. These results may greatly facilitate the development of heat-tolerant and eco-friendly plant-based lubricants using O.violaceus seed oil and improve our understanding of the genomic evolution of Brassicaceae.

Synergistic Lubricating Performance of Graphene Oxide and Modified Biodiesel Soot as Water Additives

The tribological performance of graphene oxide (GO) nanosheets, modified biodiesel soot (MBS) nanoparticles, and their mixture (MBS–GO) nanoparticles as lubricant additives in water was evaluated using a reciprocating ball-on-plate tribometer. The effects of different mass ratios of GO to MBS, additive concentrations, and loads, as well as corresponding lubrication mechanisms, were studied. The tribological measurements showed that the water-containing 0.5 wt% additives at a mass ratio of 60:40 (GO to MBS) resulted in larger reductions in friction coefficient (69.7%) and wear volume (60.5%) than water. Owing to the synergistic effect of GO nanosheets and MBS nanoparticles, the MBS–GO aqueous sample showed superior lubricating properties compared to water as well as GO and MBS aqueous samples. The good tribological properties of MBS–GO nanoparticles in water are attributed to the formation of a tribofilm of hybrid nanoparticles that effectively protects the friction interface. Moreover, the MBS nanoparticles can provide lubrication by acting as ball bearings.

Nanofriction Properties of Mono- and Double-Layer Ti3C2Tx MXenes.

Unique structure and ability to control the surface termination groups of MXenes make these materials extremely promising for solid lubrication applications. Due to the challenging delamination process, the tribological properties of two-dimensional MXenes particles have been mostly investigated as additive components in the solvents working in the macrosystem, while the understanding of the nanotribological properties of mono- and few-layer MXenes is still limited. Here, we investigate the nanotribological properties of mono- and double-layer Ti3C2Tx MXenes deposited by the Langmuir-Schaefer technique on SiO2/Si substrates. The friction of all of the samples demonstrated superior lubrication properties with respect to SiO2 substrate, while the friction force of the monolayers was found to be slightly higher compared to double- and three-layer flakes, which demonstrated similar friction. The coefficient of friction was estimated to be 0.087 ± 0.002 and 0.082 ± 0.003 for mono- and double-layer flakes, respectively. The viscous regime was suggested as the dominant friction mechanism at high scanning velocities, while the meniscus forces affected by contamination of the MXenes surface were proposed to control the friction at low sliding velocities.