Lubricant-infused Surfaces Research Articles

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.

Fabrication of stable slippery lubricant-infused porous surface on polymethyl methacrylate/thermoplastic polyurethane by supercritical CO2 foaming

The development of sustainable and efficient methods to prepare slippery lubricant-infused porous surface (SLIPS) is a profound work. In this study, using bilayer polymers restricting foaming mutually, bimodal cells were prepared through bilayer poly(methyl methacrylate) (PMMA). At the same time, uniform cells were prepared by bilayer PMMA /thermoplastic polyurethane (TPU). The prepared porous surfaces exhibited a high porosity (57% or more). TPU as dispersed phase increased the cell density of the PMMA/TPU surface with a maximum cell density of 5.5 × 107 cells/cm2 and an average cell size of 1.0 μm. SLIPS prepared on PMMA/TPU surface with high porosity and uniform microcellular had better stability, and the sliding angle (SA) remained less than 10° after centrifugal rotation at 8000r/min. Therefore, this work provides an approach to improve the surface cell density and produce SLIPS sustainably and efficiently.

A facile approach to fabricate a stabilized slippery lubricant-infused porous surface with dynamic omniphobicity for self-cleaning.

Developing a slippery lubricant-infused porous surface (SLIPS) is an important strategy for fabricating dynamically omniphobic surfaces. In this study, biocompatible and non-toxic liquid silicone rubber, TiO2 nanoparticles, and dimethyl silicone oil were used to fabricate a SLIPS. Subsequently, systematic investigation was conducted to explore its associated properties and address existing challenges in this field. The chosen lubricant exhibited a strong chemical affinity towards the substrate, eliminating the need for any functionalization treatment prior to infusion. In addition, the fabricated SLIPS exhibited excellent dynamic omniphobicity as well as shear stability, thermal stability, chemical stability, and mechanical stability. Moreover, it demonstrated good self-cleaning performance for droplets, with varying surface energies, temperatures, and pH values, as well as for common dyes and contaminants. In addition, damage from external forces could self-repair on the SLIPS, which is beneficial for extending the service life and application range.

Molecular Interaction Mechanisms Between Lubricant-Infused Slippery Surfaces and Mussel-Inspired Polydopamine Adhesive and DOPA Moiety.

Lubricant-infused slippery surfaces have recently emerged as promising antifouling coatings, showing potential against proteins, cells, and marine mussels. However, a comprehensive understanding of the molecular binding behaviors and interaction strength of foulants to these surfaces is lacking. In this work, mussel-inspired chemistry based on catechol-containing chemicals including 3,4-dihydroxyphenylalanine (DOPA) and polydopamine (PDA) is employed to investigate the antifouling performance and repellence mechanisms of fluorinated-based slippery surface, and the correlated interaction mechanisms are probed using atomic force microscopy (AFM). Intermolecular force measurements and deposition experiments between PDA and the surface reveal the ability of lubricant film to inhibit the contact of PDA particles with the substrate. Moreover, the binding mechanisms and bond dissociation energy between a single DOPA moiety and the lubricant-infused slippery surface are quantitatively investigated employing single-molecule force spectroscopy based on AFM (SM-AFM), which reveal that the infused lubricant layer can remarkably influence the dissociation forces and weaken the binding strength between DOPA and underneath per-fluorinated monolayer surface. This work provides new nanomechanical insights into the fundamental antifouling mechanisms of the lubricant-infused slippery surfaces against mussel-derived adhesive chemicals, with important implications for the design of lubricant-infused materials and other novel antifouling platforms for various bioengineering and engineering applications.

Temperature-driven sustainable anti-scaling on phase-change lubricant-infused surface

Temperature-driven sustainable anti-scaling on phase-change lubricant-infused surface

A rationally designed polymer brush/lubricant coating system for effective static and dynamic marine antifouling

Bioinspired slippery surfaces have garnered significant attention as promising solutions to mitigate biofouling. Unlike traditional lubricant-infused porous surfaces, recent research has focused on the integration of lubricants within polymer brush-grafted surfaces. The combination of polydimethylsiloxane (PDMS) polymer brush and silicone oil has gradually become the most prevalent choice due to their outstanding chemical affinity. However, this conventional coating system also has the potential for improvement to meet the needs of long-lasting and efficient marine antifouling, including i) precisely designing the polymer brush’s chemical structure to match the polarity of a specific lubricant enhances their chemical affinity, and ii) appropriately reduce the coating system’s surface energy to improve the fouling desorption performance. Here, we introduce a systematically engineered polymer brush/lubricant coating system that incorporates fluorinated polysiloxane and perfluoropolyether fluid. This novel coating system exhibits enhanced adhesion strength coupled with reduced surface energy, resulting in superior stability and omniphobic properties. Additionally, it showcases excellent corrosion resistance and significantly deters marine microorganism adhesion, achieving reductions of 98.8 % for P. tricornutum and 99.8 % for Bacillus sp.. Marine field trials, conducted over a 90-day static immersion period, confirm the remarkable antifouling performance, which surpasses most existing slippery coatings. Moreover, under dynamic conditions, organisms adhering for 150 days are readily dislodged by shear force. These findings underscore the pivotal role of systematic design in polymer brush/lubricant coating systems for the advancement of high-performance slippery surfaces tailored for marine antifouling applications.

Micro- and Nanoengineered Metal Additively Manufactured Surfaces for Enhanced Anti-Frosting Applications.

The greater geometrical design freedom offered by additive manufacturing (AM) as compared to the conventional manufacturing method has attracted increasing interest in AM to develop innovative and complex designs for enhanced performance. However, the difference in material composition and surface properties from conventional alloys has made surface micro-/nanostructuring of AM metals challenging. Frost accretion is a safety hazard in numerous engineering applications. To expand the application of AM, this study experimentally investigates the antifrosting performance of superhydrophobic and slippery lubricant-infused porous surfaces (SLIPSs) generated on AM alloy, AlSi10Mg. By strategically utilizing the subgrain structure in the metallography of the AM alloy, the functionalized superhydrophobic AM surface featuring hierarchical structures was shown to greatly reduce frost formation as compared to functionalized single-tier structured surfaces, hierarchical structures formed on conventional aluminum alloy surfaces, and SLIPSs. Optical observation of frost propagation demonstrated that the mechanism of frost delay is governed by the inhibition of spontaneous droplet freezing through exceptional Cassie state stability during condensation frosting. The Cassie stability results from the unique AM structure morphology, which creates a higher structural energy barrier to prevent condensate from infiltrating the cavities. This phenomenon also enables the formation of a high surface-to-droplet thermal resistance, which eliminates spontaneous droplet freezing down to a -15 °C surface temperature. Our work demonstrates a scalable structuring method for AM metals, which can result in delayed frost formation, and it also provides guidelines for the development of engineered surfaces requiring the antifrosting function for several industries.

Contact-angle hysteresis provides resistance to drainage of liquid-infused surfaces in turbulent flows

Lubricated textured surfaces immersed in liquid flows offer tremendous potential for reducing fluid drag, enhancing heat and mass transfer, and preventing fouling. According to current design rules, the lubricant must chemically match the surface to remain robustly trapped within the texture. However, achieving such chemical compatibility poses a significant challenge for large-scale flow systems, as it demands advanced surface treatments or severely limits the range of viable lubricants. In addition, chemically tuned surfaces often degrade over time in harsh environments. Here, we demonstrate that a lubricant-infused surface (LIS) can resist drainage in the presence of external shear flow without requiring chemical compatibility. Surfaces featuring longitudinal grooves can retain up to 50% of partially wetting lubricants in fully developed turbulent flows. The retention relies on contact-angle hysteresis, where triple-phase contact lines are pinned to substrate heterogeneities, creating capillary resistance that prevents lubricant depletion. We develop an analytical model to predict the maximum length of pinned lubricant droplets in microgrooves. This model, validated through a combination of experiments and numerical simulations, can be used to design chemistry-free LISs for applications where the external environment is continuously flowing. Our findings open up new possibilities for using functional surfaces to control transport processes in large systems. Published by the American Physical Society 2024

The preparation and characterization of lubricant-infused silicone rubber surface based on laser-splicing-scan microstructure

Slippery surface, as the most cutting-edge function surface, has aroused the extensive attention ascribed to excellent hydrophobicity and self-cleaning property. Micro/nanostructure (functional carrier) and lubricant fluid (functional layer) collectively constitute slippery bi-phase surface. To our best knowledge, we firstly validate the preparation feasibility of lubricant-infused silicone rubber surface (LISRS) based on nanosecond laser splicing scan. Comprehensive characterizations demonstrate that laser splicing traces will break the uniformity of microstructures resulting in droplet pinning. However, the lubricant infusion can significantly endow the whole microstructure surfaces with droplet depinning effect, which directly improves the process compatibility of the laser splicing machining. The capillary infiltration and unstable loss of the lubricant on the microstructure surfaces not only confirm the stable lubricant layer of LISRS conformal with microstructures, but also reveal capillary stabilization mechanism of microgroove structures under gravity environment. Then, after being subjected to comprehensive stability tests (including mechanical abrasion, water droplet and jet impacts), the water droplet sliding behaviors of impacted surfaces show that the lubricant-infused microstructure surface has a certain degree of resistance to external impacts. These results show that it is extremely feasible to create large-scale LISRS using a laser splicing scan. With the rapid development of laser micro/nanofabrication, it is promising to break through the tough issue of large-scale and high-efficiency preparation of slippery silicone rubber surfaces, and bring slippery surfaces to the practical applications of anti-corrosion, anti-fouling and anti-icing materials or products.

Comparison and investigation of edible hydrophobic coatings on beeswax and carnauba wax oil gels

In our daily life, it often uses all kinds of liquid food, such as cola, fruit juice and other drinks. Whenever you finish using these, you will find that there will inevitably be residual liquid at the bottom of the bottle that cannot be poured out, resulting in a considerable waste. However, in recent years, the emergence of lubricant infused surface (LIS) can be used to solve this problem. In this research, LIS is prepared by forming an oleogel with shellac and linseed oil, which has the advantage that the experimental raw materials require low cost, the materials are easily available, and do not cause health hazards to human beings. To gain a deeper understanding of the mechanism of LIS antifouling, the effects of optimal Brazilian carnauba wax content and beeswax content on the surface morphology, water contact angle and sliding angle, chemical functional groups, transmittance, and oil-holding rate of LIS were investigated, and the effects of liquid foodstuffs antifouling were tested with optimal Brazilian carnauba wax and beeswax content, respectively.

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.

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

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

Underwater Bubble Manipulation on Surfaces with Patterned Regions with Infused Lubricants.

The flexible manipulation of underwater gas bubbles on solid substrates has attracted considerable research interest from scientists in the fields of water electrolysis, bubble microreactions, drug delivery, and heat transfer. Inspired by the oxygen-binding mechanisms of aquatic organisms, scientists have designed a series of interfacial materials for use in collecting gases, detecting and grading bubbles, and conducting microbubble reactions. Aerophilic surfaces are commonly used in underwater bubble manipulation platforms due to their excellent gas-trapping properties. However, during bubble transport, some of the bubbles are retained in the rough structure of the aerophilic surface and cause gas loss, which in the long run reduces the gas transport function. In addition, the aerophilic surface is prone to failure in high-humidity and high-pressure underwater environments. The lubricant-infused surface features an oil layer that remains stable on a rough substrate and is immiscible with water. Additionally, the bubbles are transported over the oil layer without causing losses other than those dissolved in water. These attributes make it more favorable than the aerophilic surface. Inspired by the unique properties of Nepenthes and cactus spines, we developed a patterned slippery surface [patterned lubricant-infused surface (PLIS)] through laser etching and ammonia etching that facilitates the coexistence of superaerophobic and aerophilic surfaces. The PLIS executes bubble capture utilizing a difference in wettability measuring 78°, transports bubbles through Laplace force and buoyancy, and regulates bubble release by restricting the contact area on the PLIS. The PLIS can be prepared rapidly and affordably in just about an hour, and its potential for large-scale production is high. Following tests for shear, acid and alkali resistance, and corrosion resistance, the PLIS exhibited impressive weathering resistance and appears to have potential for application in some extreme environments.

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

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

Bioactivated lubricant-infused surfaces: A dual-action strategy for enhancing osseointegration and preventing implant-associated infections

Implant-associated infections (IAIs), caused by bacterial adhesions and biofilm formations on the implant surfaces, have been the most critical threat for orthopedic surgeries. A promising strategy to prevent IAIs involves modifying the implant surface to inhibit undesirable adhesions. In particular, lubricant-infused surfaces demonstrate exceptional anti-fouling and antibacterial properties. However, their extreme anti-fouling nature also hinders the adhesion of essential biomolecules and cells, including osteogenic cells vital for bone-implant integration. Successful implantation of orthopedic implants demands strong osseointegration as well as antibacterial properties. In this study, we designed a bone morphogenetic protein 2 (BMP-2) immobilized lubricant-infused surface (BILS) that promotes selective osteoblast adhesion while effectively preventing undesired biosubstance adhesions. BILS exhibits excellent repellency against various liquids (sliding angle less than 5°), proteins (coverage less than 1%), and bacteria (colony-forming units 10-fold less than bare substrate). Notably, BILS enhances osteoblast adhesion, reaching 30% coverage after one day and proliferating up to 70% after three weeks. We also confirmed osteoblast differentiation on BILS through alkaline phosphatase activity and calcium assays as early and late markers, respectively. BILS-applied intramedullary nails were implanted into a rabbit femoral fracture model to investigate the antibacterial and osteogenic effects of BILS in vivo. Through histological, radiographic, and biomechanical tests, BILS was confirmed to exhibit both antibacterial as well as osseointegration properties, suggesting that BILS is a rational approach to orthopedic implants without side effects.

Nanorough Is Not Slippery Enough: Implications on Shedding and Heat Transfer.

Lowering droplet-surface interactions via the implementation of lubricant-infused surfaces (LISs) has received important attention in the past years. LISs offer enhanced droplet mobility with low sliding angles and the recently reported slippery Wenzel state, among others, empowered by the presence of the lubricant infused in between the structures, which eventually minimizes the direct interactions between liquid droplets and LISs. Current strategies to increase heat transfer during condensation phase-change relay on minimizing the thickness of the coating as well as enhancing condensate shedding. While further surface structuring may impose an additional heat transfer resistance, the presence of micro-structures eventually reduces the effective condensate-surface intimate interactions with the consequently decreased adhesion and enhanced shedding performance, which is investigated in this work. This is demonstrated by macroscopic and optical microscopy condensation experimental observations paying special attention at the liquid-lubricant and liquid-solid binary interactions at the droplet-LIS interface, which is further supported by a revisited force balance at the droplet triple contact line. Moreover, the occurrence of a condensation-coalescence-shedding regime is quantified for the first time with droplet growth rates one and two orders of magnitude greater than during condensation-coalescence and direct condensation regimes, respectively. Findings presented here are of great importance for the effective design and implementation of LISs via surface structure endowing accurate droplet mobility and control for applications such as anti-icing, self-cleaning, water harvesting, and/or liquid repellent surfaces as well as for condensation heat transfer.

Room-temperature endogenous lubricant-infused slippery surfaces by evaporation induced phase separation.

We present a novel approach to fabricate endogenous slippery lubricant-infused porous surfaces (eSLIPS) at room temperature using an evaporation-induced phase separation process. The ternary coating system, comprising ethylene-propylene copolymer, caprylyl methicone, and n-hexane, forms a porous structure in situ infiltrated with lubricant, resulting in surfaces with remarkable anti-fouling and anti-icing properties.

Simple fabrication of anisotropic slippery lubricant-infused surface for directional transportation and anti-corrosion by metal-metal laminated composites

Slippery lubricant-infused surfaces with anisotropy for directional transportation have been widely researched and fabricated. However, the preparation of the required surface morphology remains complex and challenging. Inspired by the laminated structure found on natural shell nacre and slippery characteristics of nepenthes, a simple and universal method was provided to fabricate anisotropic slippery lubricant-infused surface. 304/TC4 metal-metal laminated composites were prepared by diffusion bonding 304 stainless steel and TC4 titanium alloy foils. A regular micro array with grooves was obtained through simple chemical etching. The widths of grooves and bulges, as well as the depths of grooves could be adjusted as needed. After the chemical modification, the lubricant was infused into grooves to obtain anisotropic slippery lubricant-infused surfaces. The directional transportations along the grooves of water droplet in air and bubbles underwater were achieved on the fabricated surfaces. Furthermore, the achieved surfaces demonstrated outstanding performance in anti-corrosion and anti-fouling. A noteworthy advantage of using laminated composites to fabricate anisotropic slippery lubricant-infused surfaces lies in its simplicity, universality, and repeatability. Based on the previous reports about laminated composites, the structure with grooves can been obtained by simple chemical etching. This method is suitable for various materials, including metal, ceramic, carbon material, and polymers. It has great potential application in water collection, directional transportations, anti-corrosion and anti-fouling.

Lubricant-infused anodic aluminum oxide surface (AAO-LIS) for durable slipperiness under harsh conditions

The wettability of surfaces plays a crucial role in determining their applications, and slippery surfaces have been utilized in various fields. Especially, lubricant-infused surface (LIS) has been undergone extensive research over the past decade. However, LIS tends to lose its infused lubricant and consequently lose its slippery properties when exposed to harsh conditions. Therefore, there is a strong need to enhance the durability of the infused lubricant. Herein, two strategies are adopted to improve the durability of slippery properties against centrifugal forces and high-speed shear flows. One strategy is using re-entrant shaped nanocavities, and the other is grafting PDMS brush onto the surface. Anodic aluminum oxide (AAO) is employed to fabricate the re-entrant shaped nanocavities, and the durability of the infused lubricant is improved when the cavities have a smaller diameter. Furthermore, the re-entrant shape of nanocavity significantly improves the durability compared to nanocavity with a constant diameter. The grafting of PDMS brush is essential for enhancing the durability, and an increase in the length of the PDMS brush also improves the durability. The fabricated AAO-based LIS (AAO-LIS) maintains the slippery properties for 50 min under a high-speed water flow of 12 m/s. In addition, it maintains its superior slipperiness for more than a few days when exposed to actual seawater. Furthermore, the frictional drag reduction performance of the fabricated AAO-LIS is assessed. The proposed AAO-LIS maintains a certain drag reduction performance durably even after losing its superior slipperiness, demonstrating its strong potential for practical applications across various industrial fields.