Lubricant Loss Research Articles

Slippery coating without loss of lubricant

Inspired by Nepenthes pitcher plant, slippery liquid-infused porous surface (SLIPS) has been received great concern. However, the fabrication and application of SLIPS generally cannot avoid the complicated construction of the micro/nanostructures and the loss of the lubricant. In addition, despite another slippery covalently surface can exhibit liquid-like properties of SLIPS, the chemical grafting reaction conditions are usually harsh and low-efficiency. To address these challenges, herein an easy, high-efficiency and non-fluorinated strategy to create a flat slippery coating without the loss of lubricant (SCLL) was reported. The better flatness and the own hydrophobicity of the cured polyorganosilazane (PSZ) combined with the silicone oil molecules on its surface endowed the SCLL excellent slippery property. Moreover, the strong intermolecular attraction and the large adhesion work originated from the chemical affinity between PSZ and silicone oil molecules allowed the proposed SCLL with no lubricant loss. We further showed the SCLL has promising application prospects in the ice resistance, indicated by its longer icing-delaying time and lower ice adhesion strength, compared with original Al surface. Our envision is that SCLL may be applied in the practical industry production.

Design of stable liquid infused surfaces: Influence of oil viscosity on stability

Slippery liquid-infused porous surfaces (SLIPS) have been used as a good alternative for superhydrophobic coatings due to their increased durability against mechanical forces and their ability to repel liquids with a wide range of surface tensions. SLIPS generally consists of a superhydrophobic porous structure infiltrated with a lubricant. The self-healing ability of SLIPS helps to maintain their water repellency longer than superhydrophobic surfaces. Even though SLIPS have great functionalities for practical applications, their stability is still insufficient due to the loss of lubricant from them. The oil loss from SLIPS depends mainly on the viscosity of the lubricant infiltrated into it. Even though plenty of research has been conducted over SLIPS with viscosities ranging from 1 cSt to 20, 000 cSt, a complete understanding of the oil loss mechanism is still not available. Therefore, in this work, we investigated the influence of silicone oil (lubricant) viscosity on the stability of SLIPS to determine a suitable viscosity range to fabricate stable SLIPS. Various SLIPS were fabricated by infiltrating silicone oils with a wide viscosity range. Stability studies were conducted by obtaining the volume of oil removed from the SLIPS with respect to the number of drops. Narrow SLIPS were also fabricated to understand the effect of self-healing speed on the oil loss process. Finally, a dynamic wicking experiment is conducted to determine the self-healing speed of silicone oils. SLIPS with silicone oil viscosities of 3000 cSt and 5000 cSt demonstrated lower loss rates and higher stability. However, the oil loss was fastest for SLIPS with 100 cSt silicone oil. Rapid self-healing of the lower viscosity oil was the main reason for the quick oil loss from lower viscosity SLIPS.

Heat-flow coupling variation in double-row tapered-roller bearings during the loss of lubrication process

Loss of lubrication (LOL) is a severe problem in transmission systems wherein the temperature increases continuously until failure. The temperature and flow-field distributions during this process are complicated. These distributions and the heat generation of the transmission system during LOL have not been adequately studied. In this study, we used computational fluid dynamics to establish an oil–gas, two-phase flow model for asymmetric bearings and calculated the oil volume fraction on the bearing surface. A dynamic heat generation calculation method was proposed based on the kinematic viscosity variation of the oil–air mixture during the LOL process. The temperature distributions of the large and small rollers and raceway surface during the LOL process were analyzed using a simulation method. The injection parameters were optimized to avoid the gluing of the large roller. The internal temperature distribution was found to have a strong positive correlation with the lubricant distribution during the LOL process. Moreover, the lubrication and temperature distributions on the large-roller side were worse than those on the small-roller side. A temperature reduction of approximately 25% can be achieved if the number of oil inlets is increased.

Management of osteoarthritis: From drug molecules to nano/micromedicines.

With the change in lifestyle and aging of the population, osteoarthritis (OA) is emerging as a major medical burden globally. OA is a chronic inflammatory and degenerative disease initially manifesting with joint pain and eventually leading to permanent disability. To date, there are no drugs available for the definitive treatment of osteoarthritis and most therapies have been palliative in nature by alleviating symptoms rather than curing the disease. This coupled with the vague understanding of the early symptoms and methods of diagnosis so that the disease continues as a global problem and calls for concerted research efforts. A cascade of events regulates the onset and progression of osteoarthritis starting with the production of proinflammatory cytokines, including interleukin (IL)‐1β, IL‐6, tumor necrosis factor (TNF)‐α; catabolic enzymes, such as matrix metalloproteinases (MMPs)‐1, ‐3, and ‐13, culminating into cartilage breakdown, loss of lubrication, pain, and inability to load the joint. Although intra‐articular injections of small and macromolecules are often prescribed to alleviate symptoms, low residence times within the synovial cavity severely impair their efficacy. This review will briefly describe the factors dictating the onset and progression of the disease, present the current clinically approved methods for its treatment and diagnosis, and finally elaborate on the main challenges and opportunities for the application of nano/micromedicines in the treatment of osteoarthritis. Thus, future treatment regimens will benefit from simultaneous consideration of the mechanobiological, the inflammatory, and tissue degradation aspects of the disease.This article is categorized under:Nanotechnology Approaches to Biology > Nanoscale Systems in BiologyImplantable Materials and Surgical Technologies > Nanotechnology in Tissue Repair and Replacement

Facilely Fabricated Self-Lubricated Photothermal Coating with Long-Term Durability and External-Replenishing Property for Anti-Icing/Deicing.

Icing has a severe negative impact on daily life and equipment stability. The slippery liquid-infused porous surface (SLIPS) has been widely studied for icephobicity. However, loss of lubrication leads to the failure of icephobicity. In this work, a self-lubricating photothermal surface (SLPS) based on multiwalled carbon nanotubes (MWNTs) and silicone oil was fabricated by a facile preparation method to realize passive anti-icing/deicing and active deicing simultaneously. SLPS can inhibit frost formation, delay freezing, and reduce ice adhesion strength (τice) under low-light and dark conditions. The τice value of SLPS-5-2 was 5.82 kPa in the absence of light at -20 °C. MWNTs improve the oil locking ability and inhibit oil loss, enhancing durability. The τice value of SLPS-5-2 remained within 20 kPa during 30 icing cycles. Meanwhile, SLPS has the excellent external replenishment capability to recover icephobicity. In addition, SLPS shows excellent photothermal deicing performance to melt frost, droplets, and ice layer quickly. Icing can be removed fast due to the oil layer. Silicone oil enhances the lateral heat transfer, improving the photothermal deicing. This all-in-one integration of the self-lubricating and photothermal effect finally boosts icephobicity compared to the traditional SLIPS or individual photothermal materials toward environmentally compatible and solar-driven icephobicity.

CFD-Based Analysis of Oil and Gas Two-Phase Flow Characteristics in Double-Row Tapered Roller Bearings with Different Rib Structures

In this study, two-row tapered roller bearings (TBR) with different rib structures were tested under the condition of loss of lubrication. It was found that the double-row TBR with outer ring rib structure worked normally after 40 min of the test, but the inner ring The bearing of the side structure has failed. In order to explain this phenomenon, computational fluid dynamics (CFD) numerical simulation models of two structural bearings were established, and the flow characteristics of the oil in the bearing cavity under the conditions of full lubrication and loss of lubrication were studied by the method of discrete inlet oil volume. The research results show that, in the fully lubricated state, the oil volume fraction of the double-row TBR outer ring wall of the outer ring rib structure is 11.296 times higher than that of the inner ring rib structure. Moreover, the volume fraction of oil on the roller surface is 2.07 times higher in the outer ring rib structure than the inner ring rib structure. The volume fraction of lubricating oil in the bearing cavity decreases as the speed increases; however, the double-row TBR with the outer ring rib structure still shows a better lubrication effect than the inner ring rib structure. In the final stage of the loss of lubrication, the volume fraction of the bearing flow field of the outer ring rib structure is twice that of the inner ring rib structure, making the outer ring rib structure double-row tapered roller bearing (TBR) more dry Operational ability.

Slippery Coating Without Loss of Lubricant

Slippery Coating Without Loss of Lubricant

Effect of the third body layer formed at different temperature on fretting wear behavior of 316 stainless steel in the composite fretting motion of slip and impact

316 SS is a commonly used material for steam generator tube. The object of this investigation is to study the influence of temperature, which is 95 °C and 250 °C, on the formation of the third body layer (TBL), and the role of TBL on the fretting wear behavior of 316 SS. Thus, the fretting wear experiment between 316 SS tube and 316 SS plate was carried out in the composite fretting motion of slip and impact in pure water environment. The experiment time was set as 24 h, 48 h, 72 h and 120 h. The results show that at 95 °C, TBL is hard and attaches closely to the surface, which can lead to uniform abrasion and result severe microploughing between the base materials. While at 250 °C, the existence of thick TBL can avoid direct contact between base materials, and it can be easily deformed by shear forces due to its ductility, which acts as a lubricant and reducing volume loss and wear coefficient. Finally, we can conclude that temperature affects the formation mechanism and properties of TBL, thus changing the fretting wear behavior.

Easily fabricated icephobic surface with external and self-replenishing properties

Ice accretion has adverse effects on outdoor equipment, and slippery liquid-infused surface has attracted increasing attention due to its low ice adhesion strength (τice) and great potential in practical application. However, the surface lubricant loss leads to the failure of icephobicity in this system. In this paper, the icephobic surface with external and self-replenishing properties (RDLS) is prepared to enhance anti-icing and deicing properties by the facile method with infusing the silicone oil and fumed silica into the epoxy resin adhesive. As an outcome, the prepared RDLS exhibit anti-icing and deicing properties, and it also shows mechanical durability. Meanwhile, the use of fumed silica is proposed to act as a reservoir for silicone oil to extend the lifetime of oil-releasing properties. The icephobicity of the coating can also be improved by the proper amount of fumed silica. Furthermore, obtained RDLS showed superior sustainability, and the silicone oil in the coating can be replenished easily. The problem of icephobic failure caused by lubricant loss is solved effectively. This work provides a new and facile way to fabricate an icephobic coating with external and self-replenishing properties.

An eco-impact design metric for water lubricated bearings based on anticipatory Life Cycle Assessment

Water lubricated bearings have been named in literature as a sustainable alternative to their oil-based counterparts. In order to clarify when water lubricated bearings are or are not a sustainable alternative, and inform design decisions, an analytical design tool is introduced based on anticipatory Life Cycle Assessment (LCA). This model is based on data from the bearing geometries, materials, and material combinations that have been the subject of research attention in the past 20 years in water lubricated bearing design. The model provides simple equations, fed with data from literature on materials, production and their tribological combination to provide initial insight on the sustainability of these types of bearings and future designs. A case study illustrates that quantifying environmental impacts can help determine when lubricant loss is more important than material choice, or vice-versa. The method aids bearing designers towards more sustainable designs.

Mathematical model of brush seals for gas turbine engines: A nonlinear analytical solution

Presented herein is a mathematical model employing differential equations formulation for brush seals used in gas turbine engines. These components are used to seal the bearing chamber from the environment and reduce the loss of lubricant in the atmosphere, ensuring a MTBR long enough to have required the change the seals only during the engine overhaul operation. The model assumes a single curved bristle loop in the form of a curved-bridge beam subjected to the influences of complex external loads (static and dynamic). Further, a model for clustered bristles is proposed. Specifically, the static forces acting on the curved-bridge beam include the weight of the oil capillary attached to the beam, the weight of the beam itself, the capillary force developed between the surfaces of the bristles in the brush and the temperature gradient. The dynamic forces include the leakage oil pressure and the rotation of the shaft. This complex loading induces a nonlinear large deflection on the curved-bridge beam. Also, the temperature gradient present on the bristles during the gas turbine engine operation generates a change in the geometry of the beam and in the magnitude of the forces acting on the bristles modeled as beams. In the present model, the weights are assumed as uniformly distributed forces on the surface of the beam while the capillary forces and the force generated by the rotating shaft are considered to be non-uniform. The equation expressing the curvature of the beam under general loading force is developed and one can choose the appropriate method of solving the generated differential equation after the expression of the general force is defined. Hence, the ordinary differential equation describing the nonlinear large deflection of the curved-bridge beam will be derived using general nonlinear elasticity theory.

Scalable Slippery Omniphobic Covalently Attached Liquid Coatings for Flow Fouling Reduction.

Fouling and accretion have negative impacts on a plethora of processes. To mitigate heterogeneous nucleation of a foulant, lowering the surface energy and reducing surface roughness are desired. Here, we develop a multilayer coating to mitigate solution-based heterogeneous fouling for internal flows. The first layer is a sol-gel silicon dioxide (SiO2) coating, which acts as a corrosion barrier, creates the surface chemistry needed for covalent bonding of the slippery omniphobic covalently attached liquid (SOCAL), and ensures an atomically smooth (<1 nm) interface. The second layer bonded to SiO2 is SOCAL, which further reduces the nucleation rate due to its low surface energy (<12 mJ/m2). The presence of a consistent sol-gel SiO2 base coating to bind to the SOCAL enables application to various metallic substrates. The coating is solid, making it more durable when compared to alternative slippery liquid-infused surfaces (LIS) that suffer from lubricant loss. To demonstrate performance and scalability, we apply our coating to the internal walls of aluminum (Al) tubing and test its fouling performance in a flow-fouling setup with single-phase flow of synthetic seawater. The seawater consists of saturated calcium sulfide (CaSO4), and fouling is characterized in both laminar and turbulent flow regimes (Reynolds numbers 1030 to 9300). Our coating demonstrated a reduction in salt scale fouling by 95% when compared to uncoated Al tubes. Furthermore, we show our coating to withstand turbulent flow conditions, mechanical abrasion loading, and corrosive environments for durations much longer than LIS. Our work demonstrates a coating methodology applicable to a variety of metal substrates and internal passages to achieve antifouling in single-phase flows.

An Evaporation Model for Base Oil from Grease-Lubricated Rolling Bearings including Breathing

The film thickness decay of grease-lubricated bearings is determined by a loss of lubricant from the bearing. One of these loss mechanisms is base oil evaporation. In this article, a model is presented for evaporation where the volatiles leave the bearing by breathing. The model is applied to a typical drive cycle where the temperature is varied in time. The impact of the volatility of base oils and quality of sealing on the evaporation losses can be quantified with this model.

Antibiotic-Impregnated Liquid-Infused Coatings Suppress the Formation of Methicillin-Resistant Staphylococcus aureus Biofilms.

Medical device-associated infections are an ongoing problem. Once an implant is infected, bacteria create a complex community on the surface known as a biofilm, protecting the bacterial cells against antibiotics and the immune system. To prevent biofilm formation, several coatings have been engineered to hinder bacterial adhesion or viability. In recent years, liquid-infused surfaces (LISs) have been shown to be effective in repelling bacteria due to the presence of a tethered liquid interface. However, local lubricant loss or temporary local displacement can lead to bacteria penetrating the lubrication layer, which can then attach to the surface, proliferate, and form a biofilm. Biofilm formation on biomedical devices can subsequently disrupt the chemistry tethering the slippery liquid interface, causing the LIS coating to fail completely. To address this concern, we developed a "fail-proof" multifunctional coating through the combination of a LIS with tethered antibiotics. The coatings were tested on a medical-grade stainless steel using contact angle, sliding angle, and Fourier transform infrared spectroscopy. The results confirm the presence of antibiotics while maintaining a stable and slippery liquid interface. The antibiotic liquid-infused surface significantly reduced biofilm formation (97% reduction compared to the control) and was tested against two strains of Staphylococcus aureus, including a methicillin-resistant strain. We also demonstrated that antibiotics remain active and reduce bacteria proliferation after subsequent coating modifications. This multifunctional approach can be applied to other biomaterials and provide not only a fail-safe but a fail-proof strategy for preventing bacteria-associated infections.

Facile fabrication of fluorine-free slippery lubricant-infused cerium stearate surfaces for marine antifouling and anticorrosion application

Marine biofouling is a major technical challenge in shipping industry. The construction of green antifouling surface is a feasible solution to inhibit the marine biofouling. Liquid-infused surfaces inspired by Nepenthes have attracted widespread research in recent years with broad applications. In this work, a facile and rapid electrodeposition process was used to fabricate superhydrophobic surfaces with different morphologies (bayberry and hyacinths like structures) by changing electrodeposition time, and subsequent infusion of fluorine-free lubricant to form lubricant-infused surfaces. The properties of two kinds of superhydrophobic surfaces and two kinds of slippery liquid-infused surfaces were studied. For the lubricant-infused surfaces, the hyacinths-like lubricant-infused surface exhibited the best antifouling properties by preventing 95% adhesion of Phaeodactylum tricornutum and 97% adhesion of Bacillus sp., due to the nanosheet structures on the top of the microspheres offered a strong capillary force to minimize lubricant loss. Compared with superhydrophobic surface, the lubricant-infused surfaces exhibited better antifouling and anticorrosion properties. This study could shed some light on the construction of green antifouling technology.

Simulation analysis of the effects of friction on the performance of pressure regulator for drip tape

Pressure regulators (PRs) are critical equipment to ensure the safety and uniformity of irrigation systems, and their performance and stability are affected by the friction produced by the seal rings. This paper addresses the effects of friction on the performance of a drip tape inlet PR sealed by an O-ring. A dynamic numerical model considering the friction force was developed. The performance of the PR and characteristics of motion of the internal moving parts under different friction levels, inlet pressures, and flow conditions were calculated and analyzed. The results show that the simulated precision for outlet pressure is improved by considering the friction and depends on the magnitude of the friction force and working stages of the PR. Compared with a corresponding model where the friction is neglected, for friction levels of 2.5 N and 5 N, the normalized root mean square error (nRMSE) of the outlet pressure decreases by 3.8% and 6.9% in the transition stage and by 0.8% and 4% in the regulating stage, respectively. According to the response characteristics of the displacement curve of the regulating cup with respect to the variation in the regulation performance curve, the performance curve can be divided into three stages: the pressure raising stage, the transition stage and the regulating stage. Friction causes obvious outlet pressure fluctuations in the latter two stages by affecting the displacement increments of the moving parts, especially in the transition stage. Greater friction corresponds to greater fluctuations (expressed in terms of the variation coefficient of outlet pressure, CV) in the regulation performance curve, and the fluctuation amplitude increases with increasing flow rate. A PR with greater friction has a smaller applicable flow rate range to remain below a certain CV limit. When the friction is less than 7.5 N, the PR is suitable for a flow range of 400–1000 L/h. The rate of variation in the outlet pressure (δPout) increases as the friction increment and flow rate increase and the inlet pressure decreases. δPout can be greater than 20%, mainly in the transition stage and when the friction increment is greater than 7.5 N. Considering the changes in outlet pressure caused by the lubricant loss and O-ring aging during long-term use of PRs, regular inspection and maintenance are recommended for PRs installed downstream of a submain, especially ones with long drip tapes.

Facile fabrication of slippery lubricant-infused porous surface with pressure responsive property for anti-icing application

In this research, a facile template method was developed to prepare the slippery lubricant-infused porous surface (SLIPS). The porous framework consisted of polydimethylsiloxane (PDMS) and softener, and inert dimethyl silicone oil was filled into the pores as the lubricant. Under small external pressure, the sample could be easily compressed, resulting in silicone oil being extruded to the sample surface to improve the surface lubricity. In the absence of pressure, the silicone oil was stored inside the SLIPS. This pressure responsive property avoided long-term exposure and rapid loss of lubricant. By adjusting the content of softener, the pressure responsive property was tuned. When the mass ratio of PDMS to softener increased to 1:1, the extrusion amount of lubricant enhanced significantly and the water sliding angle decreased to approximately 20°, showing good lubricity. This sample exhibited low ice adhesion strength and excellent anti-icing durability. After 25 cycles of icing/deicing tests, the ice adhesion strength was still less than 20 kPa, and the loss ratio of lubricant was only approximately 15%.

Slippery liquid-infused porous surfaces with inclined microstructures to enhance durable anti-biofouling performances

In the development of biocompatible materials for biomedical applications, infections and their resulting inflammation responses are important issues caused typically by the adhesion of micro-organisms on medical devices. Recently slippery liquid-infused porous surfaces (SLIPS) has provided a new strategy for anti-biofouling and low-adhesion surfaces, however, there are still some bottlenecks in practical uses, particularly the loss of lubricant significantly restricts the durability and stability of SLIPS. In this paper, we micro-fabricated well-controlled micro-cavities with different profiles (vertical or inclined walls) to investigate the long-term anti-biofouling effect of SLIPS. We explored microstructure geometries in two aspects: the aspect ratio and the slope angle relevant with the Laplace pressure and the oil contact area which lead to different oil-locking abilities. High aspect ratio and inclined slope were demonstrated with better oil-locking ability as well as significantly increased anti-fouling performances. Under the same experimental setup, the Escherichia coli and Staphylococcus aureus bacteria coverage on SLIPS with 80 μm-depth 20° inclined micro-cavities was only ∼30 % of that with vertical micro-cavities, while increasing aspect ratio by 4 times induced ∼3 times enhanced anti-fouling effect. On basis of these findings, we propose the enhanced SLIPS with inclined microstructures to achieve better oil-locking ability and long-term anti-biofouling performance, which may broaden many practical applications of SLIPS.

WO3-based slippery coatings with long-term stability for efficient fog harvesting

Inspired by Nepenthes pitcher plants, slippery liquid-infused porous surfaces (SLIPSs) have attracted wide attention and exhibited remarkable liquid repellency, droplet motion control and antifouling properties. However, lubricant-impregnated surfaces have poor durability, leading to loss of control of the movements of droplets during applications. Herein, WO3-based slippery coatings with high stability were prepared by the spray method and photocatalytic reaction. Notably, on the basis of the hierarchical structures, the strong intermolecular forces between the polydimethylsiloxane brush and silicone oil led to the formation of a stable lubricant layer on the WO3-based slippery coating, which can suppress lubricant loss during water collection. After a series of stability tests, such as high-speed centrifugation, long-term storage, acidic solution and multiple heating/cooling cycles, the biomimetic slippery surface still displays excellent surface-slippery stability. Furthermore, the slippery surface exhibits superior water mist capture, water droplet expansion and harvested water removal abilities, leading to good water collection performance. The silicone oil content in the collected water was 28 mg/L, demonstrating that the loss of oil was lower during the water collection process. Even under harsh environments, including multiple heating/cooling cycles, long-term storage and high shear force, lubricant-impregnated coatings can also maintain good water collection efficiency. Therefore, these slippery coatings are promising for widespread application.

Improving the lubricating properties of transmission oils by activating the processes of boundary films formation

The properties of the boundary lubricating films determine the performance of friction units, which is most important in the event of a loss of lubricant. It has been found that when sunflower oil is added to mineral transmission oil, strong boundary layers are formed during friction. These layers reduce wear and friction. Vegetable oils with the lowest iodine value have the best antiwear properties. The additional introduction of the product of the interaction of rosin with copper (II) hydroxide into the transmission oil makes it possible to form lubricating structured layers that improve the tribotechnical properties.