Lubricant Retention Research Articles

A Different Perspective on the Solid Lubrication Performance of Black Phosphorous: Friend or Foe?

Black phosphorous (BP), a promising 2D material with exceptional electronic and optical properties, has shown remarkable potential in tribology as an additive in liquid lubrication and a composite in solid lubrication. However, its potential as the standalone solid lubricant is still at its early stage. This study evaluates BP's solid lubrication performance as deposited coating (by drop casting) on a variety of metallic substrates (polished AISI 52 100 steel, aluminum, copper, and iron) under different contact pressures using a ball‐on‐disc linear‐reciprocating test machine in dry conditions. The results demonstrate that BP does not systematically reduce friction and wear. Depending on the contact pressure and the characteristic of the substrate material (particularly surface roughness), its friction and wear behavior vary a great deal. The best results observed are a 33% reduction in friction with increased surface roughness on iron and a 23% reduction in wear on aluminum. While no general trend is observed for contact pressure effects, increased substrate roughness proves beneficial, enhancing lubricant retention and exploiting BP's low interlayer shear mechanism. Therefore, this study demonstrates that while promising, BP's solid lubrication performance is not exceptional. It also highlights the importance of optimizing test conditions and materials for enhanced lubrication.

A fluorine-free bioinspired multifunctional slippery coating for ultra-long-term anticorrosion of Mg alloy, static/dynamic anti-icing, antibacterial and antifouling

Poor corrosion resistance limits the application of Mg alloy and it is meaningful to explore a surface coating technology for ultra-long-term corrosion protection of Mg alloy. Superhydrophobic surface (SHS) and smooth liquid-injected porous surface (SLIPS) have shown important application value in the field of Mg alloy corrosion protection. However, the unstable special interface of air layer or lubricant cannot act as stable corrosion barrier for the long term. Inspired by frog skin, a bionic fluorine-free multifunctional slippery coating (MSC) is prepared by one-step spraying a mixture of epoxy resin, silicone oil, modified nano TiO2 and modified micron mica powder. MSC exhibits a microstructure similar to frog skin, excellent slippery (sliding angle ∼ 3°) and strong lubricant retention. Different from anticorrosion mechanism of SHS and SLIPS by their special interface, MSC, storing silicone oil on the surface and inside the coating, demonstrates ultra-long-term anticorrosion to Mg alloy (both neutral salt spray and 3.5 wt% NaCl solution immersion for 60 days) due to excellent barrier effect throughout coating, and the scratch defect area of MSC is not significantly eroded after 14 days of salt spray. Moreover, MSC exhibits excellent static/dynamic anti-icing ability and low ice adhesion in a −20℃ environment, outstanding adhesion (level 4B), high hardness (3H), antibacterial (>94 %), antifouling, chemical stability and resistance to boiling water, ice water and UV radiation. All these excellent properties can promote the application of Mg alloy in a wider range of fields.

Phospholipid Nanoemulsion-Based Ocular Lubricant for the Treatment of Dry Eye Subtypes: A Multicenter and Prospective Study.

Dry eye disease (DED) is a multifactorial condition of the ocular surface (OS) characterized by loss of tear film homeostasis, ocular discomfort, and vision disturbances. Most available ocular lubricants target the aqueous deficiency of the tear, restoring only this layer, leaving the tear lipid stratum deficient, as occurs in most patients with evaporative DED. An innovative propylene glycol-hydroxypropyl guar enriched with a phospholipid nanoemulsion (PG-HPG-PH-N) is indicated to restore deficiencies in both the lipid and aqueous layers of the tear film, and its composition was designed to increase lubricant retention on the OS. The purpose of this study was to evaluate, through the Ocular Surface Disease Index (OSDI) and clinical assessment, the treatment of patients who had DED due to aqueous deficiency arising from mixed or evaporative DED subtypes with a PG-HPG-PH-N ocular lubricant at a reduced frequency of twice a day, in a prospective, multicenter, and single-arm study. Patients were screened from days - 7 to 0, and from day 1 (baseline and first day of treatment) to day 28 of treatment with this lubricant. After visit 1 (screening visit, days - 7 to 0), designed as pre-treatment OS assessment, patients returned to their research center on days 14 and 28 of treatment for a complete assessment, including anamnesis, the OSDI, corrected visual acuity, tear breakup time (TFBUT), OS staining evaluation, tolerability index, and environmental exposure questionnaire. Seventy patients were enrolled in this study (60 women, 10 men), with a mean age of 45 (range 27-64) years. TFBUT results showed an improvement in tear film stability as vital dyes sodium fluorescein and lysamine green showed a decrease in corneal staining after 14 and 28days of treatment. No significant adverse events were reported, demonstrating the good tolerability of the lubricant. The PG-HPG-PH-N nanoemulsion can be considered to be a safe and effective ocular lubricant for treating DED due to aqueous deficiency, both mixed and evaporative subtypes. Brazilian National Research Ethics Commission (ReBEC registration number 16055).

Can Microcavitated Slippery Surfaces Outperform Micropillared and Untextured?

Surface features' morphology is crucial in designing lubricant-infused slippery surfaces (LIS). Microcavities were hypothesized to provide lower physical pinning, reduced droplet normal adhesion, and superior lubricant retention as compared to micropillars and untextured surfaces. Micropillars and microcavities (h = 10 ± 3 μm, d = 8 ± 1 μm, p = 17 ± 3 μm, rw = 1.4 ± 0.2) were replicated on polydimethylsiloxane from Lotus leaf and were coated with 1000 cSt silicone oil films (530 nm-27 μm thick). Water wetting, water-oil thermodynamic stability, droplet's normal adhesion and oil shear drainage properties were investigated to evaluate the relative performance of microcavitated, micropillared and untextured LIS. For ≤7 μm thick oil films, cavitated and untextured LIS displayed superior slippery properties than micropillared LIS (16 ± 1°, 7 ± 1°, 30 ± 4° slide-off angles respectively). Also, normal adhesion is of the order: cavities < untextured < pillars, and smaller than their dry counterparts. Furthermore, the oil retention efficiency under the action of centrifugal forces and continuous shear flow of water is of the order: pillars > cavities > untextured. Thus, it can be concluded that microcavitated LIS can outperform micropillared and untextured LIS.

Direct visualization of viscous dissipation and wetting ridge geometry on lubricant-infused surfaces

Drops are exceptionally mobile on lubricant-infused surfaces, yet they exhibit fundamentally different dynamics than on traditional superhydrophobic surfaces due to the formation of a wetting ridge around the drop. Despite the importance of the wetting ridge in controlling drop motion, it is unclear how it dissipates energy and changes shape during motion. Here, we use lattice Boltzmann simulations and confocal microscopy to image how the wetting ridge evolves with speed, and construct heatmaps to visualize where energy is dissipated on flat and rough lubricated surfaces. As speed increases, the wetting ridge height decreases according to a power law, and an asymmetry develops between the front and rear sides. Most of the dissipation in the lubricant ( >75%) occurs directly in front and behind the drop. The geometry of the underlying solid surface hardly affects the dissipation mechanism, implying that future designs should focus on optimizing the surface geometry to maximize lubricant retention.

LASER SURFACE TEXTURING TO IMPROVE THE TRIBOLOGICAL PROPERTIES OF Ti ALLOYS

Friction and wear requirements in the aerospace/space industry or in biomedical applications are governed by life-limiting challenges: the wide range of contact stresses and sliding speeds in movable parts and operating conditions such as extreme temperature changes, humidity and abrasive wear caused by electrostatically attracted dust. Surface modification by laser texturing has been introduced to adjust the surface characteristics of the base material to overcome its tribological limitations of use via different surface topographies, allowing for the ability of lubricant retention. Laser surface texturing is therefore effective in enhancing the tribological performance of materials via controllable surface topographies acting as traps for wear debris and lubricant reservoirs, leading to reduced abrasion. This paper reviews the tribological behaviour of a laser-textured Ti6Al4V alloy with different textures: lines, crosshatch and dimples. The fiction and wear characteristics for dry sliding are discussed and compared.

Comparative Analysis of Microabrasive Film Finishing Effects across Various Process Variants.

The paper investigates various methods of microfinishing and arrives at the best technique to produce a very smooth surface. Various setups, with and without oscillation, were developed, together with a microfinishing attachment used on conventional lathes and milling machines. The workpiece material used was an amorphous nickel-phosphorus Ni-P alloy. The surface roughness parameters, such as Sa, Sv, and Sp, were measured with the TalySurf CCI6000 instrument. For the measurement of the surface protrusions, an "analysis of islands" technique was used at various levels of cut-off. The 2BA method-machining below the workpiece axis with oscillation-turned out to be the most effective method applied because it had the highest density of protrusions while having the smallest value of surface roughness. Non-oscillation with the machining zone below the axis also becomes effective, indicating that repositioning can compensate for a lack of oscillation. Already, the very compact surface structure achieved with minimized depths in the valleys by the 2BA method supported the improvement in tribological performance and increase in load-carrying capacity, together with lubricant retention enhancement. These results show that the microfinishing process can be optimized by parameter tuning, and also, non-oscillating methods could come to be a practical alternative, probably reducing the complexity of equipment and cutting costs. Further studies need to be aimed at the scalability of these methods and their application to other materials and fields.

PDMS-brush modified dual-phase lubricant-infused slippery oleogel for sustainable shear resistance

The strong potential of oleogel surfaces in marine environments is to reduce frictional drag. Conventional slippery surfaces, while resistant to water pollutants, face challenges in retaining infused lubricants under intense marine shear flows, rendering them vulnerable to fouling by marine foulants. Further, there is a critical need to develop a simple, rapid, and environmentally benign process for fabricating durable oleogel surfaces. In this study, we proposed a covalently cross-linked dual-phase (solid/liquid) lubricant-infused slippery oleogel for the first time to achieve excellent shear stable lubrication performance by rapid one-step grafting of poly(dimethylsiloxane) (PDMS) brushes (solid lubricant) on erucamide-crosslinked PDMS composite surface followed by infusion of liquid-lubricant. Covalent attachment of liquid-like slippery PDMS brushes on the dual-phase slippery oleogel (denoted as EPC-PB oleogel) further enhanced lubricant retention ability, resulting in longevity of lubrication property even after exposure to various physical abrasions, chemically-contaminated solutions, and high/low temperatures. The chemically modified oleogel exhibited droplet-sliding behavior, coupled with sustained high lubrication in marine environments, without any fouling adhesion for over 2 months during the summer season. Given its exceptional slippery performance and ease of manufacture, the proposed coating has immense potential to address the issue of lubricant depletion in high-speed marine flow scenarios.

Fabrication of a scalable slippery surface via novel sprayable breath figure technique for sustainable drag reduction and anti-biofouling in marine environments

The maritime industry has been seeking efficient solutions to combat hydrodynamic friction and biofouling, which increase operational costs and environmental issues. To address these concerns, we developed a novel sprayable breath figure (sBF) method to create a scalable and cost-effective lubricant-infused surface (LIS) for reducing frictional drag forces on marine vehicles. The proposed sBF method facilitated the rapid production of multilayered porous polymer films with micron-scale spherical cavities. It can be applied to large and curved surfaces, thus overcoming the limitations of traditional breath figure methods. Further surface treatment of oxygen plasma etching followed by polydimethylsiloxane (PDMS) brush grafting was employed to optimize the interfacial slip and lubricant retention of the slippery surface coating. The PDMS brush-grafted slippery surfaces demonstrated significant drag reduction under turbulent flow conditions. This was confirmed by direct velocity field measurements, showing nonzero slip velocity unlike conventional no-slip surfaces. The same surfaces also exhibited remarkable anti-biofouling performance, severely resisting marine biofouling in real-sea field tests over 50 days. The proposed sBF method was successfully applied to large-area and curved submerged bodies, and achieved a noticeable drag reduction under high-speed turbulent flows. This study is a critical step toward the practical implementation of this technology in the marine industry.

Tribological Synergism of Anodic Aluminum Oxide Surface Containing Micro-Holes and Nanopores under Lubricated Reciprocation

Micro-drilled aluminum surfaces containing micro-holes were anodized to produce nanopores over the machined and lapped surfaces. The anodized nanopores had an approximate diameter of 30–40 nm and a depth distribution of 20–30 μm from the surface. The diameter and depth of the machined micro-holes were 125 μm and 300 μm, respectively. Anodization itself did not change the surface roughness because the nanopores were very small. Ball-on-disk reciprocating tests were performed under lubricated conditions for 2 h using a frequency of 2 Hz, a load of 2 N, and a travel distance of 5 mm. The results showed that both the micro-drilled and anodized surfaces greatly reduced the coefficient of friction compared with the lapped bare surface; however, the coefficient of friction of the hole-textured specimen was not maintained till the end. Contrary to expectations, the lubricant retention capability of the textured structure declined because of hole failure that occurred during oscillation. This gradually increased friction until the end of the reciprocating test. When the micro-drilled surface was anodized, the coefficient of friction decreased again, implying that non-anodized micro-holes alone were ineffective for reducing friction. The surface hardness of Al increased owing to anodization, and thus the micro-holes remained intact. Therefore, it is concluded in this study that a prerequisite for friction reduction in Al is to increase the hardness to minimize the failure of micro-holes, which can be achieved by anodization. The synergistic lubricant retention capability can be maintained by the presence of both nanopores and micro-holes.

Multifunctional slippery photothermal coating

Slippery liquid-infused porous surface (SLIPS) has shown significant application values in various areas and has been commonly obtained by injecting the water-immiscible lubricant into a low-surface-energy modified micro/nano-structured surface. Constrained by the availability of desirable structured substrates or simple preparation schemes, the exploration of SLIPS with multifunctionality and universality that is facile to fabricate and robust in realistic applications remains challenging. Herein, we propose a one-step, fluoride-free and unconventional protocol based on a one-pot reaction of polysilazane (PSZ), silicone oils and multiwalled carbon nanotubes (MWCNT), which creates not only the favorable micro/nano-scale physical structures and surface chemistry for the excellent slippery property (sliding angle < 3°) and robust lubricant retention, but also the superior photothermal responsiveness for the potential multifunctional applications. It has been demonstrated that the proposed multifunctional slippery photothermal coating (MSPC) displayed outstanding potential in corrosion resistance, droplet manipulation and anti/de-icing. We envision that the proposed strategy could be realized in the real-life applications.

Infusing paraffin-based lubricant into micro-/nanostructures for constructing slippery marine antifouling coatings

Slippery liquid-infused porous surfaces (SLIPS) have enormous potential to substitute for traditional antifouling coatings due to green broad-spectrum antifouling properties. However, the serious loss of lubricants is a major problem in their applications. Herein, anodic aluminum oxides (AAO) with different morphologies were prepared, modified with siloxane and infused with paraffin-based lubricant to explore the lubricant retention capacity of specially-designed AAO. The results showed that pyramid-like cluster structures on the porous surface can offer large space to store more lubricant, forming a barrier to alleviate lubricant loss to a certain extent. Paraffin added to silicone oil crystallized and nucleated through a phase transition by temperatures to reduce the rheological properties of the lubricant and improve its stability. The combination of unique surface structures in AAO and the infusion of paraffin-based lubricant can ensure the long-lasting storage and conservation of the lubricant in AAO, moreover, the thermally sensitive paraffin-based framework can quickly switch and the dispersed silicone oil provided liquid-repellency properties. Antifouling tests showed that paraffin-based SLIPS demonstrated a reduced adhesion of the Phaeodactylum tricornutum to 96 % as compared to that of the flat aluminum alloy surface. This work shows that the combination of the geometric features of substrate and the fluid properties of paraffin-based lubricant can broaden the applications of SLIPS in marine antifouling technology.

Design of an anticorrosion/bactericidal dual functional organic coating based on the slippery liquid-infused porous surface

In this work, a long-lasting slippery liquid-infused porous surface (SLIPS) was fabricated on an organic coating to achieve both anticorrosion and antibacterial functions. Phenyl-modified etched basalt (PEB) scales were produced to construct micro-nano capillary structures and generate π electrons, which facilitated the retention of lubricant on the surface when assembled onto an epoxy resin layer. Plant oil was selected as a lubricant to introduce numerous –COOH, and was robustly trapped on the surface by π-COOH interactions, which enhanced the durability of the SLIPS coating. Based on the electrochemical tests, the coating displayed superior anticorrosion performance with |Z|0.01Hz values of 1.99 × 1010 Ω·cm2 after 14 days of immersion, which benefited from excellent barrier effect and liquid repellency. The zeta potential result proved that the corrosion resistance of SLIPS coating was further improved by the electrostatic repulsion. In addition, the antibacterial experiment results demonstrated only 0.32% of biofilm coverage and no live bacteria after 3 days of immersion, which implied the dual mechanisms of SLIPS coating in killing bacteria and inhibiting bacterial adhesion. The SLIPS coating with excellent lubricant retention and promising anticorrosion/bactericidal performance possesses tremendous application potential in marine protection.

Facile fabricant of slippery lubricant-infused porous foam-like surface for efficient fog harvesting

Inspired by pitcher plant, a variety of lubricant-infused surfaces have been created with unique properties. Owing to its high heat transfer performance and negligible contact angle hysteresis, the lubricant-infused surfaces are employed in fog harvesting. However, the loss of lubricant oil can result in performance degradation. Therefore, many surfaces with fine micro/nano structure have been created to increase the lubricant retention ability of lubricant-infused surface. Unfortunately, the procedures for preparing these surfaces are difficult or time-consuming. In this study, we synthesized a porous foam-like lubricant-infused surface (F-LIS). Porous copper foam was created on the surface of copper sheets through the dynamic bubble template method, and the pore walls were made of closely interlaced needle-like nano-dendrites. The fog harvesting efficiency of the surface can reach 2761.2 mgcm−2h−1. Additionally, F-LIS demonstrates excellent mechanical durability and chemical stability as a result of the micro/nano structure and the strong intermolecular force between PFPE as lubricant and the modifier layer, PFDT. After high-speed rotation, prolonged placement and UV irradiation etc., the surface still exhibits brilliant sliding ability and fog harvesting efficiency. This work offers a simple and effective approach for fabricating lubricant-infused surfaces with distinguished fog harvesting capability, providing a reference for relieving the crisis of freshwater resource scarcity.

Exploring the potential of nano technology: A assessment of nano-scale multi-layered-composite coatings for cutting tool performance

Nano-scale Multi-layered Composite Coatings (Nano scale MLCC) offer potential benefits for cutting tool performance. Such coatings can be designed to improve tool durability and cutting efficiency by providing additional wear protection and improved heat dissipation. The Nano coatings can also be tailored to reduce friction, which can enhance productivity and reduce tool wear. The unique Nano-scale topography of MLCC helps to reduce the contact area between the cutting tool and the workpiece, thus reducing friction and heat. The coatings also include specific additive components that enhance the properties of the coating, such as corrosion resistance, lubricant retention, and improved thermal stability.This critical review explores the potential of Nano-scale multi-layered-composite coatings for improving the performance of cutting tools. The literature in this field is reviewed and discussed with respect to the performance benefits and challenges associated with the implementation of these nanotechnology coatings. The latest progress in nanofabrication, nanomaterials, and other technologies are discussed in relation to their ability to provide new and improved cutting tool applications. The review summarizes the current state of the art on Nano-scale multi-layered-composite coatings and their influence on cutting tool performance, with particular focus on machining productivity, tool life, cutting forces and wear rates. Recommendations are provided on which Nano-scale coatings may best fit the demands of particular machining operations, and on future research directions in this field. The review also discusses the challenges and future advancements of Nano-scale coatings and other methods for improving cutting tool performance. In conclusion, this review provides a comprehensive insight into the future potential of MLCC for cutting tool performance enhancement.

Durability of Slippery Liquid-Infused Surfaces: Challenges and Advances

Slippery liquid-infused porous surfaces (SLIPS) have emerged as a unique approach to creating surfaces that can resist fouling when placed in contact with aqueous media, organic fluids, or biological organisms. These surfaces are composed of essentially two components: a liquid lubricant that is locked within the protrusions of a textured solid due to capillarity. Drops, immiscible to the lubricant, exhibit high mobility and very-low-contact-angle hysteresis when placed on such surfaces. Moreover, these surfaces are shown to resist adhesion to a wide range of fluids, can withstand high pressure, and are able to self-clean. Due to these remarkable properties, SLIPS are considered a promising candidate for applications such as designing anti-fouling and anti-corrosion surfaces, drag reduction, and fluid manipulation. These collective properties, however, are only available as long as the lubricant remains infused within the surface protrusions. A number of mechanisms can drive the depletion of the lubricant from the interior of the texture, leading to the loss of functionality of SLIPS. Lubricant depletion is one challenge that is hindering the real-world application of these surfaces. This review mainly focuses on the studies conducted in the context of enhancing the lubricant retention abilities of SLIPS. In addition, a concise introduction of wetting transitions on structured as well as liquid-infused surfaces is given. We also discuss, briefly, the mechanisms that are responsible for lubricant depletion.

Degradation analysis of tribologically loaded carbon nanotubes and carbon onions

Coating laser-patterned stainless-steel surfaces with carbon nanotubes (CNT) or carbon onions (CO) forms a tribological system that provides effective solid lubrication. Lubricant retention represents the fundamental mechanism of this system, as storing the particles inside the pattern prevents lubricant depletion in the contact area. In previous works, we used direct laser interference patterning to create line patterns with three different structural depths on AISI 304 stainless-steel platelets. Electrophoretic deposition subsequently coated the patterned surfaces with either CNTs or COs. Ball-on-disc friction tests were conducted to study the effect of structural depth on the solid lubricity of as-described surfaces. The results demonstrated that the shallower the textures, the lower the coefficient of friction, regardless of the applied particle type. This follow-up study examines the carbon nanoparticles’ structural degradation after friction testing on substrates patterned with different structural depths (0.24, 0.36, and 0.77 µm). Raman characterization shows severe degradation of both particle types and is used to classify their degradation state within Ferrari’s three-stage amorphization model. It was further shown that improving CNT lubricity translates into increasing particle defectivity. This is confirmed by electron microscopy, which shows decreasing crystalline domains. Compared to CNTs, CO-derived tribofilms show even more substantial structural degradation.

Surface roughness and morphology evaluation of bearing steel after grinding with multilayer graphene platelets dispersed in different base fluids

Bearings are widely used in different industries which demand different quality requirements to ensure a long life with low wear rates. In this sense, bearing components should present combination of low surface roughness and tight dimensional deviations, as well as good lubricant retention capacity. So, grinding is an alternative to achieve this combination, however, one of the challenges is the large amount of heat generated in the grinding wheel-workpiece interface when using conventional abrasives grinding wheels, which can lead to surface finish deterioration and thermal damages, thereby reducing the component's life. Thus, several cooling-lubrication techniques have been tested in the past decades to enhance the cooling-lubrication properties of cutting fluids, with a highlight in recent years for the benefits of adding solid particles with good tribological properties to improve grinding efficiency. In this context, this work sought to evaluate the roughness and surface morphology of the bearing steel SAE 52100 (60 ± 2 HRC) after grinding with multilayer graphene (MLG) platelets dispersed in two different cutting fluids (synthetic and semi-synthetic). Tests with traditional MQL (without solid particles) and conventional techniques (flood) were also carried out for comparison. The output variables investigated were surface roughness parameters Ra, Rz, Rku, Rsk, Rk, Rpk, and Rv, images of machined surfaces through a scanning electron microscope (SEM), and the specific grinding energy. The results indicated that the base fluid type significantly affected the grinding performance. Tests with semi-synthetic fluid having MLG decreased the Ra parameter of the ground surface by 9% compared to the traditional MQL technique, with a higher Rvk and negative skewness. For the synthetic fluid also with MLG, about 29% increase in the Ra parameter was observed compared to MQL without nanoparticles, although it resulted in higher values of Rpk with more positive skewness. Presence of MLG in semi-synthetic and synthetic fluids reduced the specific grinding energy by 7% and 14%, respectively. Also, less intense plastic deformation and material adhesion was observed when grinding with MLG.

Sustainable Drag Reduction of Fatty Acid Amide‐Based Oleogel Surface Under High‐Speed Shear Flows

AbstractNepenthes alata‐inspired micro/nano‐textured lubricant‐infused surface (LIS) has shown strong potential in the fields of drag reduction (DR), anti‐biofouling, and self‐cleaning. However, its surface‐slippery property is largely degraded under turbulent shear flow conditions due to the loss of the impregnated oil. This condition inhibits its practical applications to marine vehicles. The mucus‐impregnated tissue systems of marine creatures are primarily based on fatty acid amides (FAAs), such as erucamide or oleamide, which have been commercially utilized as solid‐slip additives. A stable lubricant interface of erucamide‐PDMS composite (EPC) oleogel is formed by cross‐linking erucamide with PDMS gel network prior to infusion of silicon oil. In this study, the surface stability and lubricant retention of EPC are investigated in consideration of DR applications. The fabricated EPC‐oleogel surface exhibits shear stable DR under harsh conditions, such as high pressure, temperature, and shear flow conditions. The surface shows a shear stable DR performance of about 14% even up to a high‐speed flow of 12 ms−1, corresponding to friction Reynolds number (Reτ) of approximately 5000. The superior lubrication stability of FAA‐oleogel at the flow conditions of cruising ships ensures its strong potential for sustainable fuel economy of marine vehicles.

Characterization of the Liquid–Lubricant Interface in a Dovetail Cavity for a Viscous Laminar Flow

Lubricant-infused surfaces (LISs) have application in diverse fields based on their liquid-repellent properties. In bulk flow, LISs, however, are susceptible to drainage failure caused by external shear imposed at the liquid–lubricant interface. In this study, the shear-flow-induced lubricant depletion in a dovetail-shaped cavity microchannel has been numerically examined. Lubricant is exposed to five external liquids with different viscosities (μr = 0.2–1) in the laminar range (100 ≤ Re ≤ 1000). Temporal variations in the lubricant depletion from the microchannel and cavities were observed with time. Meniscus shapes were characterized for flows at different viscosity ratios. The results show that when the lubricant is kept fixed, a less viscous external liquid aids in better lubricant retention. Due to the shear imparted, three stable and two failure meniscus shapes have been distinguished. The results are further supported by vortex formation within the cavity and interface velocities contributing to meniscus shapes based on the magnitude of external shear. Additionally, it was evident that, as the viscosity ratio was reduced, the effect of the cavity opening was no longer dependent on the flow rate. It was envisaged that the results will help in the design of a robust LIS system.