Lubricant-infused Surfaces Research Articles

Self-Adjusting Lubricant-Infused Porous Hydrophobic Sticky Surfaces: Programmable Time Delay Switch for Smart Control of the Drop's Slide.

Although strategies for smart control of droplets by utilizing slippery surfaces that are typically made by infusing lubricants into porous surfaces are booming, no surface can smartly control the start or stop of droplet sliding without external environmental stimuli. A strategy for how surfaces alone, if constituted by lubricant-infused porous hydrophobic sticky surfaces (LIPHSS) with a specific interface self-adjusting system, can achieve the target of smart control of a drop's slide is presented here. The continuous self-adjustment of the interface formed by droplets and LIPHSS leads to the occurrence of droplet sinking behavior. The droplet's sinking reduces its sliding angle (SA) and thus can trigger the sliding of the droplet deposited on LIPHSS with a tilt base angle between the SA after sinking and the SA before sinking. Furthermore, regulating lubricant layer thickness and tilt base angle is an important way to achieve smart control of the time required to initiate the sliding of the droplet. The uniqueness of the study is focused on the clever extension of the sinking behavior of droplets on LIPHSS to achieve a programmable time delay switch to smart control the sliding of droplets.

Fabrication of multifunctional wax infused porous PVDF film with switchable temperature response surface and anti corrosion property

The discovery of the lubricant infused surface (LIS) embarked a promising approach on the active surface applications. Demonstrated here is an intricately designed multifunctional film influenced by bottom-up approach, utilizing the underlying features of the compounding materials to provide greater functionalities and opportunities for various applications. Through facile fabrication method, a porous film was generated by incorporating ZnO nanoparticle as a porogen onto PDVF polymer prior casting followed by simple acid washing for the removal of ZnO. Wax was used to lubricate the porous thin film; the design was inspired by the advantageous property of the wax that will enhance surface wetting properties, exhibiting the surface with thermal responsiveness, anticorrosion protection and robust structure. By taking advantage onto the lubricant’s rheological property, droplet motion control in response with the temperature variation was explored. Surface responses on different kinds of liquids were also studied. The multifunctional film manifested anticorrosion protection, which is supported by electrochemical measurement technique. The film’s stability was explored through exposure on harsh condition that successfully preserve its robust architecture.

Durable deicing lubricant-infused surface with photothermally switchable hydrophobic/slippery property

Lubricant infused surfaces (LISs) are promising platforms to address the icing problems, but their long-term stability remains a significant challenge. In this study, a durable LIS with photothermal response and reversible solid/liquid transformation was fabricated to rapidly thaw frost accumulation and reduce ice accretion. The newly designed LIS was manufactured by infusing low-melting cocoa oil and efficient photothermal Fe3O4 nanoparticles into anodized aluminum oxide substrate. Upon irradiation with infrared light, the Fe3O4 nanoparticles could absorb light energy and melt the solid lubricant into slippery liquid. The dual actions of surface heating and slipperiness of melted lubricant promoted the thawing of frost/ice and de-adhesion of ice block. Additionally, the durability of LIS was strengthened by the combination of the self-healing effect of the melted lubricant, and the robustness of the solid state. The hydrophobic lubricant diminished the lubricant loss during repeating freezing/unfreezing cycles and withstood longtime flowing water impact. The proposed concept of switchable hydrophobic/slippery lubricant will advance the design of durable LISs and provide a promising LIS platform for deicing application.

Fabrication of transparent icephobic surfaces with self-reparability: Effect of structuring and thickness of the lubricant-elastomer layer

Biomimetic lubricant-infused slippery surface (LISS) has attracted extensive attention as an alternative to a superhydrophobic surface (SHS) for icephobic applications. In this work, the impact of the material parameters of LISS with a lubricant-elastomer layer on icephobic performance is reported. A layer of polydimethylsiloxane elastomer and silicone oil on smooth and structured polypropylene (PP) surfaces was spin-coated by a simple one-step procedure. Results demonstrate that the ultra-smooth lubricant-elastomer layer (LEL) has an extremely low water contact angle hysteresis. Compared to SHS and smooth surface, the LISSs reduced ice adhesion by an order of magnitude due to its molecular homogeneity, low contact area, and strain mismatch. The LISSs exhibited excellent dynamic mobility at −10 °C, shear stability, evaporation resistance, mechanical robustness, and transparency. Physically damaged LISS can self-repair at 80 °C. The change in structures and LEL thickness of structured PP has little effect on ice adhesion. As the LEL thickness on a smooth PP increases, the ice adhesion decreases. The smooth PP with a thick LEL has very low ice adhesion, indicating that the roughness is not necessary for maintaining the slippery properties. Transparent, stable, anti-dusting, and self-repairing LELs on smooth materials have potential for icephobic applications.

Icephobic performance of one-step silicone-oil-infused slippery coatings: Effects of surface energy, oil and nanoparticle contents

HypothesisState-of-the-art superhydrophobic surfaces (SHSs) usually do not function in high humidity and frosty climate conditions. Lubricant-infused slippery surfaces (LISSs) with a homogeneous and ultraslippery surface are expected to be a reliable icephobic technique. Hence, the fabrication of simple and scalable bioinspired LISSs is important for practical applications. ExperimentsDurable one-step LISSs consisting of silicone oil and polymer mixtures were fabricated. A grid map based on added oil and silica nanoparticles was developed to tune wettability, morphology, and slippery behavior of surfaces. A similar framework for ice adhesion of lubricant-infused coatings was also presented for the design of optimal icephobic materials. FindingsLISSs with slight hydrophobicity yield slippery properties, resulting in an order of magnitude lower ice adhesion compared to SHSs. The stable 20-w% silicone-oil-infused slippery coating with slight hydrophobicity and silica nanoparticles was found to be effective in anti-icing. The nanoparticles firmly anchor the oil overlayer and eliminate contamination by drying the surface. The LISSs made of polymers with surface energy ranging from 29 to 31 mJ/m2 show the potential to achieve low ice adhesion. As a result, the use of systematic frameworks highlights the role of material parameters. One-production strategy can be broadly used to design icephobic materials.

Photothermal Actuation of Diverse Liquids on an Fe3O4-Doped Slippery Surface for Electric Switching and Cell Culture.

The photoinduced manipulation of liquids on a slippery lubricant-infused porous surface (SLIPS) has attracted a tremendous amount of attention because of its merits of contactless stimulation and excellent spatial and temporal control. However, tedious fabrication methods by a combination of template transfer and fluorination for a photothermal-material-doped SLIPS and the lack of deeper systematically quantitative analysis with respect to droplet hydrokinetics are greatly perplexing in both academic research and industrial applications. Here we demonstrate a kind of Fe3O4-doped SLIPS by one-step femtosecond laser cross-scanning, which can readily steer diverse liquids toward arbitrary directions with a fast velocity of up to 1.15 mm/s in the presence of a unilateral NIR stimulus. The underlying mechanism is that the wettability gradient force (Fwet-grad) induced by the temperature gradient arising from asymmetric near-infrared-irradiation (NIR) loading would be generated within 1 s to actuate a targeted droplet's sliding behavior. Through tuning the NIR irradiating sites, we can slide a targeted droplet with controllable directions and routes. On the basis of fundamental physics, we have quantitatively analyzed the relationship among Fe3O4-doped content, lubricant rheological performance, droplet wettability variations, Fwet-grad, and the sliding velocity for diverse liquid species. Accordingly, we can remotely steer liquid droplets to realize the on-off state of an electrical circuit on demand, the droplet fusion of a microfluidic reactor, and the culture/inhibition of biological cells.

Epidermal Gland Inspired Self-Repairing Slippery Lubricant-Infused Porous Coatings with Durable Low Ice Adhesion

The limited durability of slippery lubricant-infused porous surfaces (SLIPS) restricts their practical applications. Inspired by the epidermal glands of skins, we developed a facile approach to durable SLIPS with gland-like storage and release functions for icephobicity. By introducing a hybrid surfactant as a lubricant into the polydimethylsiloxane (PDMS) matrix, lubricant capsules were formed and mono-dispersed in the matrix, working as gland-like structures to release lubricant. The obtained SLIPS showed durable low ice adhesion strength and thermal durability simultaneously. In detail, the enhanced durability for icephobicity was demonstrated by 20 icing/deicing tests, in which the lubricant remains on the surface; the coatings showed negligible weight loss when stored at 100 °C for 60 h, displaying pronounced thermal durability of the slippery effect. Our current strategy sheds new light on a facile fabrication of mechanically and thermally durable SLIPS for icephobicity.

Hydration lubrication of polyzwitterionic brushes leads to nearly friction- and adhesion-free droplet motion

Recently, there has been much progress in the design and application of oil-repellent superoleophobic surfaces. Polyzwitterionic brush surfaces are of particular interest, because of their ability to repel oil under water, even in the absence of micro-/nanostructures. The origin of this underwater superoleophobicity is attributed to the presence of a stable water film beneath the oil droplet, but this had not been demonstrated experimentally. Here, using optical interferometric techniques, we show that an oil droplet effectively hydroplanes over a water film, whose thickness is between one hundred and hundreds of nanometres. In addition, using a custom-built droplet force apparatus, we find the friction and adhesion forces to be in the nN range for millimetric-sized droplets. These forces are much lower than for other classes of well-known liquid-repellent surfaces, including the lotus-leaf effect and lubricant-infused surfaces, where the typical force is on the order of μN.

Guided droplet transport on synthetic slippery surfaces inspired by a pitcher plant

We show how anisotropic, grooved features facilitate the trapping and directed transport of droplets on lubricated, liquid-shedding surfaces. Capillary action pins droplets to topographic surface features, enabling transport along the feature while inhibiting motion across (or detachment from) the feature. We demonstrate the robustness of this capillary-based mechanism for directed droplet transport on slippery surfaces by combining experiments on synthetic, lubricant-infused surfaces with observations on the natural trapping surface of a carnivorous pitcher plant. Controlling liquid navigation on synthetic surfaces promises to unlock significant potential in droplet-based technologies. Our observations also offer novel insight into the evolution of the Nepenthes pitcher plant, indicating that the 'pitfall' trapping mechanism is enhanced by the lubricant-infused, macroscopic grooves on the slippery peristome surface, which guide prey into the trap in a way that is more tightly controlled than previously considered.

Stable Dropwise Condensation of Ethanol and Hexane on Rationally Designed Ultrascalable Nanostructured Lubricant-Infused Surfaces.

Vapor condensation is a widely used industrial process for transferring heat and separating fluids. Despite progress in developing low surface energy hydrophobic and micro/nanostructured superhydrophobic coatings to enhance water vapor condensation, demonstration of stable dropwise condensation of low-surface-tension fluids has not been achieved. Here, we develop rationally designed nanoengineered lubricant-infused surfaces (LISs) having ultralow contact angle hysteresis (<3°) for stable dropwise condensation of ethanol (γ ≈ 23 mN/m) and hexane (γ ≈ 19 mN/m). Using a combination of optical imaging and rigorous heat transfer measurements in a controlled environmental chamber free from noncondensable gases (<4 Pa), we characterize the condensation behavior of ethanol and hexane on ultrascalable nanostructured CuO surfaces impregnated with fluorinated lubricants having varying viscosities (0.496 < μ < 5.216 Pa·s) and chemical structures (branched versus linear, Krytox and Fomblin). We demonstrate stable dropwise condensation of ethanol and hexane on LISs impregnated with Krytox 1525, attaining about 200% enhancement in condensation heat transfer coefficient for both fluids compared to filmwise condensation on hydrophobic surfaces. In contrast to previous studies, we use 7 h of steady dropwise condensation experiments to demonstrate the importance of rational lubricant selection to minimize lubricant drainage and maximize LIS durability. This work not only demonstrates an avenue to achieving stable dropwise condensation of ethanol and hexane, it develops the fundamental design principles for creating durable LISs for enhanced condensation heat transfer of low-surface-tension fluids.

Highly transparent and robust slippery lubricant-infused porous surfaces with anti-icing and anti-fouling performances

Recently, taking advantage of slippery liquid-infused surfaces (SLIPS) has been proposed as a simple passive ice removal method. However, the process of frost formation and ice freeze on SLIPS is accompanied by the lubricant migration from the structured substrate to the surface of frozen droplets which would lead to the sacrifice of lubricant. In this paper, highly transparent and robust slippery coatings were carried out by infusing lubricant into tube-like SiO2 composite structure. The tubular material and a stack-hole composite structure contribute a lot to lock the lubricating oil, thus reducing the loss of lubricant during the icing/deicing cycles. The ultra-low ice adhesion strength (∼17 kPa) encourages the SLIPS to be a promising candidate for anti-icing applications. Moreover, capillary action within the unique structure as well endows SLIPS with the self-healing property. As a consequence, the as-prepared samples achieve long-term anti-icing stability while ensuring a glass substrate transmittance of up to 92.01%. In addition, surfaces maintain all the slippery characteristics after being directly exposed to running water for 30 min. Such good stability offers a possibility of applying SLIPS to everyday life.

Mobility of Aqueous and Binary Mixture Drops on Lubricating Fluid-Coated Slippery Surfaces.

The mobility of liquid drops on lubricant-infused slippery surfaces depends strongly on various system parameters, for example, surface energy and roughness of the underlying solid surface and surface tension and viscosity of the test and the lubricating fluids. Here, we investigate lubricant-coated slippery surfaces fabricated on smooth hydrophobic solid surfaces and examine the influence of thickness and viscosity of the lubricating oil on the velocity of aqueous drops. We also investigate the effect of surface tension of the test liquid using a binary mixture of water and ethanol, on the apparent contact angle, which further affects their slip velocity. A theoretical model, based on various dissipative forces acting in different regions of the lubricating oil and a test drop, is also presented, which elucidates the dependence of drop velocity on lubricating oil viscosity and base radius of drops of test liquids.

A novel coating system with self-reparable slippery surface and active corrosion inhibition for reliable protection of Mg alloy

Inspirations from nature have led to extensive developments of biomimetic nonwetting surfaces and intelligent self-healing technologies toward corrosion protection of metals. Integration of both intriguing features contributes to achieving diversified protections. In this work, we engineered a novel anticorrosion system composed of a plasma electrolytic oxidation (PEO) film, a layered double hydroxide (LDH) film and a lubricant-infused slippery surface on Mg alloy. The PEO film grown in situ on Mg alloy could render a moderate corrosion barrier, and the sandwiched LDH film integrated ternary roles involving loading corrosion inhibitor, anchoring lubricant and sealing PEO defects. The outermost slippery surface exhibited durable repellence against water and also self-reparable capability to surface damage. The robust and self-reparable film barrier coupled with active corrosion inhibition endowed this system with superb anticorrosion performance. The dynamic self-healing processes associated with barrier regeneration and corrosion inhibition were substantiated at microscale using scanning Kelvin probe and scanning vibrating electrode technique, respectively. It is expected that this research would shed light on the design of multifunctional anticorrosion systems for Mg alloy.

Biofilm Bridges Forming Structural Networks on Patterned Lubricant-Infused Surfaces.

Despite many decades of research, biofilm architecture and spreading mechanisms are still not clear because of the heterogenous 3D structure within biofilms. Here, patterned “slippery” lubricant‐infused porous surfaces are utilized to study biofilm structure of Pseudomonas aeruginosa, Stenotrophomonas maltophilia, and Staphylococcus aureus. It is found that bacteria are able to spread over bacteria‐repellent lubricant‐infused regions by using a mechanism, termed “biofilm bridges”. Here, it is demonstrated that bacteria use bridges to form interconnected networks between distant biofilm colonies. Detailed structure of bridges shows a spatial distribution of bacteria with an accumulation of respiratory active bacteria and biomass in the bridges. The core–shell structure of bridges formed by two‐species mixed population is illustrated. It is demonstrated that eDNA and nutrients have a strong effect on biofilm bridges formation. Thus, it is believed that biofilm bridging is important to reveal the structure and communication within biofilms.

Corrosion Protection Application of Liquid-Infused Surface with Regional Growth of LDH Films on Al Alloys

Al alloys with their easy accessibility and good workability have been extensively used in oceanic engineering area [1]. However, corrosion failure of Al alloys is a major challenge. Although Al alloys are easily oxidized to protect themselves from corrosion, reactive anions can erode metallic substrates thereby leading to corrosion failures in wet conditions [2]. There are three different strategies that can be exploited to address the challenge. First, LDH films on Al substrate and their alloys demonstrate better corrosion protection effect because the film itself also works as a strong physical barrier [3]. Second, when the superhydrophobic surface was immersed in solution, an “air valley” film was generated on the surface, acting as a protective layer against water molecules and aggressive ions in wet conditions. According to the study of By Yuekun Lai [4], a discrete TCL is energetically advantageous to drive a droplet off a superhydrophobic surface, showing lower surface adhesion. Hence, to further decrease the surface adhesive forces, we proposed the regional growth of LDH films to reduce the continuity of the three-phase (solid-air-liquid) contact line (TCL). Finally, Nepenthes pitcher survives by using micro-structure to lock in an intermediary liquid [5], so we can exploit lubricant-infused roughness surface acts as an effective self-protective layer. Here, we design a combination of these above strategies and fabricate the slippery liquid-infused surface with regional growth of LDH films on Al alloys (denoted as sample LR). The chemical compositions and morphologies of sample LR were characterized by energy-dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). Fig. 1 shows the composition and distribution of elements after hydrothermal reaction for 3h. In Fig 1(a), we can conclude that the surface consists of Zn (58.6%), O (29%), Al (11.77%), and C (0.63%), respectively. To further study the flower-like substance on the top of surface, the SEM-EDS plan scan analysis is used in Fig.1(b)~(f). From the mapping of sample, the elements concentrated on the top are Zn and O, so the flower-like structure is Zn-Al LDH layer [6]. The preparation schematic of sample LR is showed in Fig.2(a). The morphologies of the sample LR after laser engraving and hydrothermal synthesis were characterized by SEM in Fig.2(b~d), which shows the regional growth of Zn-Al LDH layer. After chemically modified by FAS, the surface exhibits an excellent superhydrophobic property. Then the krytox100 is impregnated on the hydrophobic surfaces to form lubricant-infused surface. Polarization curves obtained by electrochemical experiments are applied to investigate the anti-corrosion ability. In Fig.3, the Tafel curves are tested after the sample LR were immersed in 3.5% NaCl aqueous solution for 10 min, 5 h, 10 h and 24 h. The corrosion current density of the sample LR reduces from 3.6´10-8 A/cm2 to 1.15´10-8 A/cm2 with the corrosion time, which means that sample LR has the stronger anti-corrosion ability owing to the existence of lubricant. With the increases of corrosion time, the lubricant spreads to form a protective film on the surface. On the contrary, the corrosion current density of Al alloys increases from 1.09´10-6 A/cm2 to 1.74´10-7 A/cm2 when the corrosion time varies from 10 min to 24 h. To further explore the corrosion inhibition capability of the sample, the electrochemical impedance spectra (EIS) is measured by an electrochemical method. As shown in Fig.4, although the corrosion time increases from 10 min to 24 h, the impedance spectra of the sample LR always show a large impedance semicircle whose diameter is around several thousands of W×cm2, which is bigger than the untreated Al alloys (200~400 W×cm2). In addition, the impedance of sample LR increases and Al alloys decreases with the corrosion time. After immersed in seawater for 24 h, the Zre of sample LR augments from 1088 W×cm2 to 1411 W×cm2. Conversely, the Zre of Al alloys decreases from 401 W×cm2 to 132 W×cm2. The results are consistent well with Tafel curves. These results indicate that sample has excellent corrosion resistance in simulated seawater. Reference [1] Wan H , Lin J , Min J . Surface and Coatings Technology, 2018, 345:13-21. . [2] Olajire, A.A. J. Mol. Liq. 2018, 269:572–606. [3] Cao Y, Zheng D, Li X, et al. ACS Applied Materials & Interfaces, 2018: acsami.8b02280. [4] Lai Y, Gao X, Zhuang H, et al. Advanced Materials, 2010, 21(37):3799-3803. [5] Wang P, Zhang D, Lu Z. Colloids and Surfaces B: Biointerfaces, 2015, 136: S0927776515301880. [6] Vega, J. M.; Granizo, N.; de la Fuente, D.; Simancas, J.; Morcillo, M. Prog. Org. Coat. 2011, 70: 213-219. Figure 1

Droplet Sorting and Manipulation on Patterned Two-Phase Slippery Lubricant-Infused Surface.

Slippery lubricant-infused surfaces are composite materials consisting of a solid matrix permanently infused by a lubricant. Such surfaces have proved to be highly repellent to various liquids immiscible with the lubricant. Depending on the underlying surface chemistry, different lubricants can be used, including perfluorinated or alkylated oils. Here, we construct patterned slippery surfaces that consist of virtual channels permanently impregnated with an organic oil and surrounded by areas permanently impregnated with a perfluorinated oil. We demonstrate that water droplets preferentially occupy the organic-oil-lubricated virtual channels. Based on a simple model, we evaluate the forces acting on droplets crossing over to the regions impregnated with perfluorinated oil and show that the cloaking of the droplets plays an important role. We study the actuation of droplets in virtual oil-in-oil channels based on gravity and magnetic fields. Finally, we construct a variety of organic-oil-lubricated channel architectures permitting droplet sorting according to size. We believe that this novel approach for the formation of virtual all-liquid surface-tension-confined channels based on lubricant-infused surfaces, channel networks, or patterns will advance the field of droplet-based microfluidics. The approach presented can be potentially useful for applications in biotechnology, diagnostics, or analytical chemistry.

Durable lubricant-infused anodic aluminum oxide surfaces with high-aspect-ratio nanochannels

Recently, lubricant-infused surfaces (LIS) have emerged as a prominent class of surface technology for antifouling, anti-icing and anticorrosion applications. However, long-term corrosion exposure and mechanical damages may deteriorate the practical performance of LIS during application. In this study, a robust LIS was fabricated by the vacuum impregnation of mineral oil into anodized aluminum oxide (AAO) nanochannels with a depth of 50 μm. The impregnation of the lubricant through the entire depth of the high-aspect-ratio nanochannels was visualized under cryo-scanning electron microscopy (cryo-SEM) and also confirmed by weight gain measurements. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) tests showed that the lubricant stored in the deep nanochannels of LIS can provide excellent corrosion protection during long-term immersion. Furthermore, the as-prepared LIS demonstrated superior resistance to mechanical damage due to a self-healing effect by the lubricant. As shown by cryo-SEM observation and PDP tests, the micro-cracks formed on the LIS can be instantaneously repaired by the in-flow of the oil from the surrounding surface. In the tribological tests, the LIS also presented high wear resistance and superior mechanical durability.

Review of Micro–Nanoscale Surface Coatings Application for Sustaining Dropwise Condensation

Condensation occurs in most of the heat transfer processes, ranging from cooling of electronics to heat rejection in power plants. Therefore, any improvement in condensation processes will be reflected in the minimization of global energy consumption, reduction in environmental burdens, and development of sustainable systems. The overall heat transfer coefficient of dropwise condensation (DWC) is higher by several times compared to filmwise condensation (FWC), which is the normal mode in industrial condensers. Thus, it is of utmost importance to obtain sustained DWC for better performance. Stability of DWC depends on surface hydrophobicity, surface free energy, condensate liquid surface tension, contact angle hysteresis, and droplet removal. The required properties for DWC may be achieved by micro–nanoscale surface modification. In this survey, micro–nanoscale coatings such as noble metals, ion implantation, rare earth oxides, lubricant-infused surfaces, polymers, nanostructured surfaces, carbon nanotubes, graphene, and porous coatings have been reviewed and discussed. The surface coating methods, applications, and enhancement potential have been compared with respect to the heat transfer ability, durability, and efficiency. Furthermore, limitations and prevailing challenges for condensation enhancement applications have been consolidated to provide future research guidelines.

How Slippery are SLIPS? Measuring Effective Slip on Lubricated Surfaces with Colloidal Probe Atmoc Force Microscopy.

Lubricant-infused surfaces have attracted great attention recently and are described as slippery liquid-infused porous surfaces (SLIPS). Here, we measured the hydrodynamic drainage forces on SLIPS by colloid probe atomic force microscopy (AFM) and quantified the effective slip length over a nanothin silicone oil layer on hydrophobized [octadecyltrichlorosilane (OTS)-coated] silicon wafers. The thickness of a stable silicone oil film on OTS-Si under sucrose solution was determined to be 1.8 ± 1.3 nm and was found to induce an average effective slip length of 29 ± 3 nm, very close to that of an uninfused OTS substrate. These relatively low values of effective slip are confirmed by the relatively large macroscopic roll-off angle values of water droplets on the same substrates. Both nano- and macroscale results reflect the immobilized nature of a silicone oil layer of thickness around 2 nm within an underlying monolayer. These results have important implications in the design of drag-reducing coatings using lubricant infusion.

Slip flow through microchannels with lubricant-infused bi-dimensional textured surfaces

Lubricant-infused textured surfaces, where a secondary liquid impregnates textures, have been employed as an alternative to gas-cushioned textured surfaces. However, the drag reduction capabilities of this new class of textured surfaces in the laminar regime have not been explored. In this work, a pressure-driven flow through microchannels containing lubricant-infused bi-dimensional textures was numerically investigated to assess their slippage properties. A large parameter ranges, Reynolds numbers 1–1000; viscosity ratio 0–1; constriction ratio 0.1–10; lubricant fraction 0–1, were employed in the simulations. Upon balancing the velocity continuity and shear stress at the liquid–lubricant interface, we could capture the viscous effects of lubricant on the amount of slippage. The effective slip length was computed as a function of relevant non-dimensional flow and geometrical parameters for texture configurations such as posts and holes. A significant amount of dissipation in the lubricant phase was observed for a viscosity ratio greater than 0.1 for both the texture configurations investigated. However, an increased viscosity ratio between the lubricant and liquid bettered the performance of the posts compared to holes at low-lubricant fractions. The inertial effects on the effective slip length were alleviated with an increase in viscosity of the underlying lubricant, for a surface covered with holes compared to posts. Furthermore, it was shown that the validity of scaling laws for the effective slip length from the gas-cushioned textured surfaces to liquid-infused textured surfaces could be extended upon incorporating the effects of inertia and viscosity ratio. The results presented here will help in designing efficient lubricant-infused textured surfaces for drag reduction both in internal and external flow settings.