Lubricant Loss Research Articles

Mao-based solid-like slippery composite coating with superior corrosion resistance and robust machinery performance upon magnesium-lithium alloy LA81

Slippery liquid-infused porous surface exhibits a great potential for corrosion management with super repulsive water properties, whilst their poor adhesion to underlying materials and durability of lubricants remains a challenge. In this work, a micro-arc oxidation (MAO)-based solid-like slippery composite coating (SSC) is developed upon Mg-Li alloy LA81 by combining mechanical pinning effects of MAO and super repulsive water performance of SSC, which maximizes adhesion strength, water repulsion and sustainable corrosion protection. The SSC coatings exhibit liquid-to-solid transition under the curing effect of epoxy resin. Efficient sealing of the MAO layer is yielded through high fluidity of the liquid phase of SSC. Cured SSC can further strengthen the interface bonding with respect to underlying MAO layer, and significantly alleviate lubricant loss.

Environmentally friendly SLIPS coating based on flexible sponge: A novel approach to antifouling for ships

To mitigate the attachment of fouling organisms, Slippery Liquid-Infused Porous Surfaces (SLIPS) hold tremendous potential as a green and broad-spectrum antifouling solution, capable of replacing traditional antifouling coatings. However, the complexity of current preparation methods and the limited lifespan of lubricating oils constrain their widespread application in marine antifouling for vessels. In this study, melamine sponge (MS) was used as a substrate, and modifications were made by introducing superhydrophobic silica nanoparticles (SiO2 NPs), a biocompatible adhesive (ethyl cyanoacrylate, ECA), and a highly stretchable polymer (poly-ε-caprolactone, PCL). By combining natural surface microstructures with additional nanomaterials, we successfully obtained a superoleophilic surface, effectively capturing liquid lubricants and maintaining their long-term stability. The sponge substrate possesses distinctive contractility, with the lubricant stored in the grid spontaneously compensating for the loss of surface lubricant, thereby effectively enhancing its durability. This study provides a straightforward fabrication method with reduced manufacturing costs for environmentally friendly marine anti-fouling coatings. The approach demonstrates a prolonged cyclic anti-fouling effect, effectively advancing the development of SLIPS for anti-fouling applications in shallow marine environments.

Durable bionic honeycomb slippery liquid-infused porous surfaces with anti-icing and water-collecting properties

The slippery liquid-infused porous surfaces with nanostructures have emerged as a high-performance multifunctional surface with super-liquid repellency, low contact angle hysteresis and self-healing. However, the amount of lubricant captured by the nanostructures is extremely low, and such oil-filled functional surfaces are susceptible to lubricant loss depletion. In this research, we developed a honeycomb-inspired multidimensional lubricant-infused surface that has a good ability to lock in lubricant while providing excellent mechanical durability. The honeycomb-shaped hexagonal micropores store lubricant to stabilize the smooth oil layer, while the pine-needle shaped nano-needles in the pores retain the lubricant in the pores, making it more difficult to lose the lubricant and increasing durability. Compared to conventional nanostructured slippery liquid-infused porous surfaces, this surface ensures excellent long-term lubrication performance under extreme conditions such as cooling, high shear and water spray impact. Meanwhile the honeycomb mesh lubricant injected into the surface is able to rapidly coalesce and remove water droplets during condensation due to the presence of coarsening effect, and it also retards the formation of ice. This structure provides a new idea for anti-icing and water collection research

Power Loss and Damage Behavior of Gears Operating Under Loss of Lubrication

Abstract Geared turbofans need to withstand loss of lubrication due to inevitable off-design conditions. Additionally, the loss of lubrication specifications that have to be fulfilled are getting stricter. For a loss of lubrication event, today's geared turbofans are equipped with secondary oil supply systems. Their omission would reduce space and weight and, consequently, carbon emissions. However, this requires geared transmissions to withstand loss of lubrication events. In order to enable this, knowledge of the power loss and damage behavior of gears under loss of lubrication is required first. In this study, power loss and bulk temperature measurements of test gears under loss of lubrication on an FZG gear efficiency test rig are presented. Hertzian pressures in the pitch point up to 1723 N/mm2 and circumferential speeds up to 20 m/s were considered. The experimental results show the characteristics of increasing power loss and bulk temperatures under loss of lubrication depending on load and speed. At moderate operating conditions, no damage occurs within 20 s under loss of lubrication, whereas a load increase results in slight scuffing, and a speed increase results in severe scuffing. Oil centrifugation has a strong effect on the loss of lubrication performance. Additional experiments under reduced quantity lubrication demonstrate the impact of the remaining oil on the survivability of gears facing the loss of lubrication.

Comparison of Anti-Icing, Antifouling, and Anticorrosion Performances of the Superhydrophobic and Lubricant-Infused Coatings Based on a Hollow-Structured Kapok Fiber.

The superhydrophobic surface and slippery liquid-infused porous surface (SLIPS)/lubricant-infused surface (LIS) have attracted increasing attention owing to their multifunctionality. However, their practical applications face several problems such as complex and inefficient preparation technology, loss of lubricant, and fragile microstructures. Therefore, new strategies for preparing microstructures must be developed for constructing superhydrophobic and lubricant-infused coatings. Herein, a low-cost and high-efficiency method for developing superhydrophobic and lubricant-infused coatings based on in situ grown TiO2 on the surface of a hollow kapok fiber (KF) is reported. The anti-icing, antifouling, and anticorrosion performance of the superhydrophobic and lubricant-infused coatings are compared. The superhydrophobic coating reduces the formation and accumulation of ice. The lubricant-infused coating exhibits an extremely low ice adhesion strength and durable anti-icing properties. The superhydrophobic and lubricant-infused coatings show the outstanding antifouling property of diatom; the superhydrophobic surface exhibits superior stability over LIS without an external force field. The lubricant-infused coating shows excellent corrosion resistance and durability when immersed in a 3.5% NaCl solution. The superhydrophobic coating loses its protection as a result of the corrosion media permeating the metal substrate via the electrolytic cell and coating interface, and the lubricant-infused coating provides lasting corrosion resistance because of the lubricant filling into the interface. Although the superhydrophobic coating is fragile and the lubricant-infused coating will lose lubricant, this simple and convenient approach can be repeated to keep the coatings active. This study provides new inspiration for the fabrication of superhydrophobic surfaces and LIS based on natural products.

Astringency perception in a red wine context – a review

Astringency is not considered one of the modern gustatory tastes. The understanding of astringency perception has evolved considerably over the past eighty years, but the exact mechanism is still undefined. This review aims to identify the current theory of astringency perception in the context of red wine. While astringency perception is a complicated mechanism that is not yet well understood, much research has focused on it. The studies discussed up to now have been done using red wine or wine-derived polyphenols. In a red wine context, astringency is driven by polyphenol concentration, galloylation and degree of polymerisation. Compounds that do not bind protein but are still strong astringent agonists are present in red wine. Among them, the role of polysaccharides and oligosaccharides is not clear, as these compounds are difficult to purify in quantities large enough for use in sensory studies. The literature strongly points to astringency being a compound perception. There is a stage of early protein binding, possibly as a “neutralising” effect for small amounts of dietary tannins with little actual perception, building into a more pronounced effect as tannin concentrations increase. A loss of lubrication in the oral cavity might announce the overpowering salivary protein capacity resulting from tannin concentrations, with direct detection of some astringent compounds once protein in the salivary fluid and the salivary pellicle are depleted.

Experimental study on boundary lubricity of superficial area of articular cartilage and synovial fluid

The boundary lubrication mechanism at the articulating surface of natural synovial joints has been the subject of much discussion in tribology. In this study, to elucidate the lubricating function of the superficial area of articular cartilage and synovial fluid (SF), cartilage specimens were processed with four different treatments: gentle and severe washing with detergent, incubation in NaCl solution, and trypsin digestion to selectively remove certain constituents from the cartilage surface. Subsequently, the frictional characteristics were examined in phosphate-buffered saline (PBS) and SF against glass. Angularly reciprocating sliding tests with a spherical glass probe and square articular cartilage specimens were performed at low contact loads in the mN range to extract the frictional behavior in the superficial area of the cartilage specimens. Meanwhile, the cartilage surface was observed to confirm the effects of treatments on the morphology of the cartilage surface using a fluorescence microscope and water-immersion methods. The coefficient of friction (COF) of the prepared cartilage specimens was varied from 0.05 to over 0.3 in PBS. However, a certain group of cartilage specimens exhibited a low COF of less than 0.1 with limited variation. For the low COF group of specimens, all four treatments increased the COF in PBS to different extents, and fluorescence microscopy revealed that the integrity of the cartilage surface was deteriorated by treatments. This means that the intact cartilage surface had lubricating constituents to maintain low friction, and the removal of such constituents resulted in the loss of the intrinsic boundary lubricity of the cartilage surface. The variation in the COF of the cartilage specimens was suppressed in SF because it had a clear boundary lubrication effect on the cartilage surface. The lubricating effect of SF could be confirmed even after degenerative treatment.

New insight in characterization of red wine astringency using soft tribology method

AbstractThe variation of friction coefficient (μ) of model wine and model saliva mixtures with entrainment speed (VR) on simulated oral surfaces was evaluated by oral tribology. Combined with techniques of dynamic light scattering (DLS), atomic force microscopy (AFM), rheometer, and quartz crystal microbalance with dissipation monitoring (QCM‐D), the correlation between characteristics of the model wine and model saliva mixtures (particle size and morphology, suspension viscosity, adsorption film thickness, and viscoelasticity) and the oral lubrication loss was established. The results showed that the higher the concentration of tannin in the model wine, the larger the size of the complexes with the model saliva, and the higher the thickness, viscoelasticity, and roughness of the adsorption film formed, which resulted in the increase of friction coefficient in the boundary lubrication regime. Different from previous results, it is found that the maximum value of the friction coefficient (μmax) in the boundary regime has the best positive correlation with the astringency perception intensity of the model wine accordingly.

On the Required Energy to Break Down the Thickener Structure of Lubricating Greases

The rheology of a conventional lithium-12 hydroxystearate bearing grease changes significantly when it is subjected to mechanical shear. Often this shear energy–along with the consequent entropy–is measured and used in engineering and thermodynamic models, leading to grease life models for predicting bearing seizure due to insufficiently thick film or loss of lubricity of the base oil/grease. In this degradation process, the bonds between the individual molecules, consisting mainly of the fairly weak van der Waals bonds and/or hydrogen bonds, are broken during this shearing process. In this article, we show that only a very small portion of the shear energy is needed to break these bonds and that the vast majority is dissipated as heat due to the lubricant viscosity, also known as viscous dissipation. We model the thickener as rod-shaped fibers, wherein the grease viscosity is reduced by a factor of 5 when the length of a fiber is reduced by a factor of 2.5. The energy needed to break the bonds between the molecules to shorten these fibers is 6 to 7 orders of magnitude smaller than the energy applied by shear. Hence, it is very difficult to measure this fiber structure breakage energy from grease shear aging experiments directly.

Durable anti-icing coating with stability based on self-regulating oil storage layer

In recent years, slippery liquid-infused porous surfaces (SLIPSs) have emerged as a potential alternative to superhydrophobic surfaces (SHSs) due to their exceptional anti-icing properties. However, the current challenge lies in the significant lubricant consumption of SLIPSs, which poses a major obstacle to coating durability. In this study, we developed a durable anti-icing coating with stability (DASS), which combines SHSs and SLIPSs. By incorporating high adsorption particles and low cross-linking density rubber into the oil storage layer, the coating achieves an increased oil storage capacity while effectively inhibiting lubricant loss. Additionally, a superhydrophobic layer is introduced on the surface to ensure surface lubrication and prevent lubricant depletion. The three-layer structure enables the coating to maintain a low τice (<20kPa) during 30 icing/deicing cycles, showcasing superior de-icing durability compared to conventional anti-icing coatings. Interestingly, the original anti-icing properties of the coating can be restored through external oil replenishment. Furthermore, this coating exhibits excellent resistance against fouling, mechanical stress, chemical exposure, temperature variations, and weathering effects, making it highly suitable for practical applications in anti-icing coatings.

Astringency and its sub-qualities: a review of astringency mechanisms and methods for measuring saliva lubrication.

Astringency is an important mouthfeel attribute that influences the sensory experiences of many food and beverage products. While salivary lubricity loss and increased oral friction were previously believed to be the only astringency mechanisms, recent research has demonstrated that nontactile oral receptors can trigger astringency by responding to astringents without mechanical stimulation. Various human factors have also been identified that affect individual responses to astringents. This article presents a critical review of the key research milestones contributing to the current understanding of astringency mechanisms and the instrumental approaches used to quantify perceived astringency intensity. Although various chemical assays or physical measures mimic in-mouth processes involved in astringent mouthfeel, this review highlights how one chemical or physical approach can only provide a single measure of astringency determined by a specific mechanism. Subsequently, using a single measurement to predict astringency perception is overly idealistic. Astringency has not been quantified beyond the loss of saliva lubrication; therefore, nontactile receptor-based responses must also be explored. An important question remains about whether astringency is a single perception or involves distinct sub-qualities such as pucker, drying, and roughness. Although these sub-quality lexicons have been frequently cited, most studies currently view astringency as a single perception rather than dividing it into sub-qualities and investigating the potentially independent mechanisms of each. Addressing these knowledge gaps should be an important priority for future research.

Ice‐Shedding Endurance Enhancement of Lubricated Polyurethane NP‐GLIDE Coating Through Dual Cross‐Linking with Covalent and Hydrogen Bonds

AbstractAn NP‐GLIDE coating, featuring a liquid‐like polymer brush layer on its surface and nanopools of a grafted liquid ingredient for dewetting enablement within its matrix, is normally covalently cross‐linked (CX). This paper introduces a dually cross‐linked (DX) NP‐GLIDE coating, employing urethane bonds and H─bonds for crosslinking. Both the DX and CX coatings, utilizing poly(dimethyl siloxane) (PDMS) as the dewetting enabler, exhibit low ice adhesion strengths (τ). Post‐lubrication with silicone oil (SO), ice is readily shed under gravity from the coatings. The DX coating maintains low τ over numerous icing/de‐icing cycles, outlasting the CX coating. This durability is likely due to the lubricant‐loss‐responsive nature of the DX matrix. The matrix increases its H─bond cross‐links responding to lubricant loss and the cross‐linking density increase triggers additional lubricant release into the PDMS brush layer. This cyclic process persists over time. Under optimal conditions after 31 icing/de‐icing cycles, the lubricated DX coating demonstrates an impressively low τ of 1.8 ± 0.5 kPa. In contrast, the lubricated CX counterpart has a τ of 32 ± 11 kPa, while plain glass records a τ of 325 ± 14 kPa. This study underscores the significant potential of dual cross‐linking for enhancing ice‐shedding endurance of coatings.

Slippery Porous-Liquid-Infused Porous Surface (SPIPS) with On-Demand Responsive Switching between "Defensive" and "Offensive" Antifouling Modes.

Slippery liquid-infused porous surfaces (SLIPS) have received widespread attention in the antifouling field. However, the reduction in antifouling performance caused by lubricant loss limits their application in marine antifouling. Herein, inspired by the skin of a poison dart frog which contains venom glands and mucus, a porous liquid (PL) based on ZIF-8 is prepared as a lubricant and injected into a silicone polyurethane (SPU) matrix to construct a new type of SLIPS for marine antifouling applications: the slippery porous-liquid-infused porous surface (SPIPS). The SPIPS consists of a responsive antifoulant-releasing switch between "defensive" and "offensive" antifouling modes to intelligently enhance the antifouling effect after lubricant loss. The SPIPS can adjust antifouling performance to meet the antifouling requirements under different light conditions. The wastage of antifoulants is reduced, thereby effectively maintaining the durability and service life of SLIPS materials. The SPIPS exhibits efficient lubricant self-replenishment, self-cleaning, anti-protein, anti-bacterial, anti-algal, and self-healing (97.48%) properties. Furthermore, it shows satisfactory 360-day antifouling performance in actual marine fields during boom seasons, demonstrating the longest antifouling lifespan in the field tests of reported SLIPS coatings. Hence, the SPIPS can effectively promote the development of SLIPS for neritic antifouling.

Multi-time scale thermal tribological dynamics coupling model of the helicopter intermediate reducer under severe loss of lubrication

There is no lubrication in the contact area, which leads to a significant influence of the thermal characteristics on the friction dynamics and life of the helicopter intermediate reducer because the helicopter experiences severe loss of lubrication. In this study, for evaluating the non-linear friction dynamics and transient thermal network models of the intermediate gearbox, a multi-time scale coupling method was proposed to establish a proportional allocation method between the oil film region and the rough peak contact region of the tooth surface by considering the effect of temperature and to study the adsorption film under the condition of severe lubrication loss. The coupled thermal and kinetic characteristics of the severe lubrication loss condition were obtained by calculating the friction coefficients in the lubricated and dry-friction regions. The results showed that the friction coefficient of the bevel gear tooth surface fluctuated between 0.1 and 0.6, and the degree of the gear axis trajectory shift was more evident owing to the increase in the friction force excitation caused by the increase in the friction coefficient.

Friction power loss of continuous sine tooth profile planetary reducer

In this paper, a sine tooth planetary reducer with one tooth difference is proposed. For the proposed reducer, the equations of the oil film thickness, the meshing sliding and rolling friction power loss, and the friction power loss of the bearings for the reducer are proposed. Using these equations, the oil film thickness distribution, the meshing sliding and rolling friction power loss of the sine gear reducer plus the friction power loss of the bearings on eccentric shaft section are analyzed. The power loss of the reducer is measured and compared to the calculated values. Results show that the measured ratio of the friction power loss to input power is 27.90 %, and the calculated one is 26.53 %. The difference between them is 1.65 %. This illustrates analysis about lubrication and friction power loss of the reducer.

Elastohydrodynamic lubrication performance of PUMA-PSMA supramolecular polymer gel lubricant

In this study, free radical polymerization was employed to prepare a supramolecular polymer gelator called PUMA-PSMA, containing urea groups. The incorporation of this gelator is anticipated to enhance the heat resistance of the gel lubricant. The resulting PUMA-PSMA gels demonstrate favorable mechanical strength and the ability to recover from deformation. Additionally, the PUMA-PSMA gel has a greater film thickness compared to the base oil when the oil supply is abundant. In cases of limited lubricant supply, the PUMA-PSMA gel effectively undergoes shear thinning, reducing the duration of oil starvation. These gel lubricants help prevent the loss of lubricant to some extent and are poised to serve as an innovative type of lubricant.

Robust solid slippery coating for anti-icing and anti-sticking

The slippery liquid-infused porous surface (SLIPS) inspired by the Nepenthes plants has received great attention due to the excellent water-repellency with ultra-low sliding angle. However, the practical application of SLIPS is restricted greatly due to the inevitable loss of lubricant trapped by the micro/nanostructures and the adverse environmental impact of the fluorinated lubricant. Herein, we report a simple and efficient strategy to form a solid slippery coating without loss of lubricant. A commercially available coating with the nominal active constituent of polysilazane (PSZ) was used as the matrix and was slippery with the water sliding angle of approx. 25°. To enhance the water repellency, α, ω- hydroxy silicone oil (HSO) was added into the PSZ solution and the sliding angle of the cured composite coating decreased to approx. 7.0°. The chemical interaction between the Si-H / Si-N bonds of PSZ and the -OH group of HSO produced strong inter-molecular attraction. Acrylic resin was further added to strengthen the overall integrity of the coating and the so-obtained composite coating was durable with no loss of lubricant. Moreover, the curing of PSZ at room temperature was accelerated greatly by HSO from longer than one week to less than one day due to the above-mentioned chemical interactions between the Si-H / Si-N bonds and the -OH group. The solid slippery coating showed promising potential in preventing ice adhesion and anti-sticking to adhesive paper due to its low adhesion properties.

P. pavoninus‐Inspired Smart Slips Marine Antifouling Coating Based on Coumarin: Antifouling Durability and Adaptive Adjustability of Lubrication

AbstractSlippery liquid‐infused porous surface (SLIPS) is received widespread attention in the antifouling field because of its dynamic slippery surface, but the limited effect of physical “anti‐adherence” and the problem of lubricant loss restrict its application for practical marine antifouling. Inspired by the self‐defensive function of P. pavoninus’s poisonous mucus, a SLIPS based on the reversible chemical bonds and the antibacterial effect of coumarin (CmSLIPS) is prepared, which addresses these disadvantages by responsively adaptive lubricity and durability. The CmSLIPS enables the “locking” and “unlocking” mode between lubricant and matrix via the reversible photodimerization of coumarin. It regulates the surface lubricity to adapt to the antifouling demand. The reversible chemical bonds of lubricant and matrix reduce lubricant loss and enhance the lubricant stability and antifouling durability. In addition to the physical anti‐adhesive barrier of SLIPS, the excellent antimicrobial property of coumarin groups further enhances the “biocidal” antifouling effect to improve long‐term antifouling durability. In summary, the CmSLIPS has surface stability, durability, responsively adaptive lubricity, efficient self‐cleaning, anti‐protein, anti‐bacterial, anti‐algae, self‐healing (92.85%) properties and 150‐day marine field antifouling performance during boom seasons, which maintains the satisfactory antifouling performance in the harsh marine environment and demonstrates the promising application in neritic sea equipment.

Difference in astringency of the main pea protein fractions

Interactions between food and saliva govern complex mouthfeel perceptions such as astringency. Herein, we present a study of the interactions of salivary proteins with the main pea protein fractions that are obtained by isoelectric and salt precipitation (legumin-rich, vicilin-rich and albumin-rich fractions). The sensory evaluations performed on protein solutions by trained panelists evidenced that all three protein fractions exhibit a basal level of astringency, but that the albumin fraction was perceived as the most astringent one. All three fractions induced significant but comparable loss of salivary lubrication. Yet, when compared to the other fractions, the albumin fraction showed the formation of a thicker and more rigid film on salivary conditioning film-coated sensors as measured using a quartz crystal microbalance with dissipation monitoring (QCM-D). We also present proteomics studies on the precipitates obtained from the mixtures of saliva and pea protein fractions. Protein identification finds a pool of salivary proteins involved in non-specific interactions with all the three pea protein fractions. Yet, 13 pea proteins specific to the albumin fraction were identified as being involved in specific interactions with salivary proteins. Several of these proteins are part of the plant defense mechanisms and are likely to interact with many salivary proteins. This could explain the higher number of salivary proteins found in the precipitate induced by the albumin fraction when compared to the other two. These quantitative results increase the understanding of the complex links between plant protein-salivary protein interactions and astringency.

Blue-ringed Octopus inspired slippery coating with physico-chemical synergistic antifouling properties

Bionic superhydrophobic and slippery liquid-infused porous surfaces (SLIPS) have attracted great interest due to their antifouling properties, while the poor stability, complex preparation of porous structures and rapid loss of lubricants, as well as only possessing physical antifouling capability, have hindered their further application. Herein, inspired by the Blue-ringed Octopus’ defensive equipment of slippery skin and toxin secretion when faced with predators, an antifouling slippery coating containing repellent is easily prepared. The repellent capsaicin physically connected to the slippery networks can be activated to accelerate release in response to the changes in pH caused by bacterial secretions, and the adhesion resistance of the coating is improved by 99 % compared to aluminum plates, both conclusions confirmed by experimental and computational data. The anti-adhesive properties of the slippery surface, combined with the repellent properties of capsaicin provides the coating with excellent synergistic physico-chemical antifouling performance. This is demonstrated by the fact that the surface of the coating remains clear after contamination with proteins, bacteria and diatoms, as well as after 65 days of marine field testing. Additionally, the slippery surface has self-healing and outstanding anticorrosion ability. Therefore, the eco-friendly coating has promising application prospects in marine field for antifouling purposes.