Slippery Liquid-infused Porous Surfaces Research Articles

A biomimetic approach towards a universal slippery liquid infused surface coating.

One biomimetic approach to surface passivation involves a series of surface coatings based on the slick surfaces of carnivorous pitcher plants (Nepenthes), termed slippery liquid-infused porous surfaces (SLIPS). This study introduces a simplified method to produce SLIPS using a polydopamine (PDA) anchor layer, inspired by mussel adhesion. SLIPS layers were formed on cyclic olefin copolymer, silicon, and stainless steel substrates, by first growing a PDA film on each substrate. This was followed by a hydrophobic liquid anchor layer created by functionalizing the PDA film with a fluorinated thiol. Finally, perfluorodecalin was applied to the surface immediately prior to use. These biomimetic surface functionalization steps were confirmed by several complimentary surface analysis techniques. The wettability of each surface was probed with water contact angle measurements, while the chemical composition of the layer was determined by X-ray photoelectron spectroscopy. Finally, ordering of specific chemical groups within our PDA SLIPS layer was determined via sum frequency generation spectroscopy. The hemocompatibility of our new PDA-based SLIPS coating was then evaluated by tracking FXII activation, fibrin generation time, clot morphology, and platelet adhesion to the surface. This hemocompatibility work suggests that PDA SLIPS coatings slow or prevent clotting, but the observation of both FXII activation and the presence of adherent and activated platelets at the PDA SLIPS samples imply that this formulation of a SLIPS coating is not completely omniphobic.

Functionalized porous 316 L stainless-steel with oil reservoir against ice adhesion

Slippery liquid-infused porous surfaces (SLIPSs) are used in anti-fouling, anti-icing and anti-corrosion, but lack of long-term durability is a challenge due to lubricant depletion. SLIPS with self-lubricating properties can achieve extended durability without reapplying the lubricant. Generally, lubricant is stored close to surface, thus lubricant reservoir is limited. Here bulk of porous material acts as lubricant reservoir in 316L stainless-steel SLIPS with self-lubricating properties for lowering ice adhesion. The reservoir was fabricated by using a space holder technique in metal injection molding (MIM) with lubricant reservoir volume up to 17.3%. Surface was activated with vinyltrimethoxysilane (VTMS) to attract lubricant. Ice adhesion strength was increased up to three times against non-porous reference in ice adhesion testing using porous surface without lubrication. The best performing SLIPS showed 6.7 times lower ice adhesion against counterpart porous surface without lubricant and 1.7 times lower than non-porous reference. This self-lubrication was achieved on mechanically durable structure having an adjustable lubricant storage capacity by temperature-driven phenomenon during de-icing.

Anticorrosion strategy for magnesium alloys through a superhydrophobic approach utilizing slippery liquid-infused porous surface coating

Anticorrosion strategy for magnesium alloys through a superhydrophobic approach utilizing slippery liquid-infused porous surface coating

Slippery Liquid-Infused Porous Surfaces Containing UiO-66 Incorporated with 8-Hydroxyquinoline for Excellent Corrosion Protection of AZ31 Mg Alloys.

The conventional slippery liquid-infused porous surfaces (SLIPSs) provide relatively limited corrosion protection and self-healing performance for AZ31 Mg alloys. To this end, 8-hydroxyquinoline (8-HQ) was incorporated into a zirconium-based metal-organic framework UiO-66 through coordination (8-HQ@UiO-66), which was then dispersed into silicone oil to fabricate nanoparticle-enhanced-SLIPSs (8-HQ@UiO-66-SLIPSs). Especially, the influences of 8-HQ@UiO-66 concentration on the surface morphology, surface hydrophobicity, and corrosion resistance were studied. It was found that the surface hydrophobicity first increased and then decreased with increasing concentration, showing the highest water contact angle of 121.2° at a concentration of 1 mg mL-1 (8-HQ@UiO-66-SLIPS-1). This was attributed to the development of well-constructed hierarchical micro/nanostructures. Moreover, it also exhibited the best anticorrosion property, with the lowest corrosion current density of 1.24 × 10-10 A cm-2 and the highest impedance modulus of 9.88 × 108 Ω cm2 at 0.01 Hz, primarily associated with the synergistic interaction of 8-HQ and UiO-66. Further, the self-healing performance was evaluated using the scanning vibration electrode technique (SVET), verifying the superior self-healing performance of 8-HQ@UiO-66-SLIPS-1. Hence, the nanoparticle-enhanced-SLIPSs exhibit considerable potential in the corrosion protection of Mg alloys, thereby accelerating their extensive applications in industry.

Anti-icing performance of SLIPSs injected with different lubricants

Abstract Transmission line icing is seriously threatening the power grid to operate safely. Slippery Liquid-infused Porous Surface (SLIPS) is a latent application to solve transmission line ice cover. The matrix structure and lubricant are important components of SLIPS. However, a variety of lubricants have been used to prepare SLIPS, and there is a lack of certain theoretical guidance for selecting lubricants to prepare anti-icing SLIPS. In this paper, the effects of three lubricants on the wettability, anti-icing performance, and anti-icing durability of SLIPS were investigated. It was found that dimethyl silicone oil was more favorable for preparing anti-icing SLIPS. The SLIPS prepared from silicone oil had a complete frosting time of about 10 min longer than that of mineral oil and safflower oil and had the lowest ice adhesion strength of 4.5 ± 0.8 kPa. It also has better anti-icing durability; even after 30 repetitions of icing/deicing, ice adhesion strength is still below 20 kPa.

Surface morphology-controlled poly(ε-caprolactone) nanofiber anti-fouling coating: A promising approach for marine applications

Abstract To effectively combat marine biofouling, biomimetic anti-fouling coatings have garnered widespread attention as a novel anti-fouling method. Based on this biomimetic concept, this study adjusted the electrospinning process parameters and selected different solvent systems to effectively modify the surface morphology of poly (ॉ-caprolactone) (PCL) nanofiber coatings, developing a non-toxic anti-fouling smooth surface. These biodegradable slippery liquid-infused porous surfaces (SLIPS) coatings offer a simple way to prepare maritime anti-fouling coatings in an eco-friendly manner. They can withstand a variety of liquid, material, and microbiological contaminations.

Amyloid Proteins Adhesive for Slippery Liquid-Infused Porous Surfaces.

Biomimetic slippery liquid-infused porous surfaces (SLIPS) have emerged as a promising solution to solve the limitations of superhydrophobic surfaces, such as inadequate durability in corrosion protection and a propensity for frosting. However, the challenge of ensuring strong, lasting adhesion on diverse materials to enhance the durability of the lubricant layer remains. The research addresses this by leveraging amyloid phase-transitioned lysozyme (PTL) as an adhesive interlayer, conferring stable attachment of SLIPS across a variety of substrates, including metals, inorganics, and polymers. The silica-textured interface robustly secures the lubricant with a notably low sliding angle of 1.15°. PTL-mediated adhesion fortifies the silicone oil attachment to the substrate, ensuring the retention of its repellent efficacy amidst mechanical stressors like ultrasonication, water scrubbing, and centrifugation. The integration of robust adhesion, cross-substrate compatibility, and durability under stress affords the PTL-modified SLIPS exceptional anti-fouling, anti-icing, and anti-corrosion properties, marking it as a leading solution for advanced protective applications.

Patterned Ultraslippery Surfaces of Stainless Steel Prepared by Femtosecond Laser Ablation for Directional Manipulation of Liquid Droplets.

Slippery liquid-infused porous surfaces (SLIPS) have promising applications in chip laboratories, nanofriction power generation, and microfluidics due to their excellent properties such as good hydrophobicity and low adhesion. However, the self-driven stability of conventionally lubricated surfaces is not high, and the velocity of liquid droplets is difficult to regulate. This greatly limits the potential applications of SLIPS. A strategy is offered to prepare microporous structures of SLIPS directly on a stainless-steel substrate using femtosecond laser processing technology as the main means to realize exhibiting smoothness to liquids. At the same time, the principle of bionics is utilized, the porous structure of SLIPS is combined with the groove structure of rice leaves, or porous structures are combined with the wedge structure of shorebird beak to prepare the three-dimensional structure of SLIPS. Droplets exhibit significant individual anisotropy on three-dimensional (3D) SLIPS of leaf-like groove stripe structure in rice, enabling the precise control of droplet motion direction. When droplets are transported in wedge-shaped SLIPS with an asymmetric structure, the wedge edge can limit the direction of droplet motion while squeezing the droplet to generate Laplace pressure gradient, which achieves continuous self-driven transport of droplets. In addition, based on the above two processing strategies, an information transfer device is designed: the splicing of the self-driven transport surface with anisotropic topological channels enables the differential drive for liquid transport, which provides the conditions for the information transfer of the droplets. This strategy not only is simple and efficient but also provides new ideas for the effective development of multifunctional SLIPS as well as lab-on-a-chip and microfluidic domains.

Preparation of slippery liquid-infused porous surface with high stability by SiO2-assisted polyimide porous membrane

Preparation of slippery liquid-infused porous surface with high stability by SiO2-assisted polyimide porous membrane

Effect of lubricant loading in slippery liquid-infused surface for persistent anti-icing performance

Due to the vast applications in biomedical materials and aerospace industry, smart slippery liquid-infused porous surfaces (SLIPSs) have attracted remarkable attention. However, there are still challenges in the fabrication of durable SLIPS. In this work, based on linear polyurea and silicone oil, a series of durable anti-icing surface were fabricated. Based on the long-lasting secretion of lubricant, the ice adhesion strength of 60-PUa was 2.7 ± 0.5 kPa and could remain below 10 kPa even after 30 icing-deicing cycles. And the icing delay time of 60-PUa could be extended up to 870 s at a temperature of −15 °C. The introduction of large numbers of reversible hydrogen bonds in the system and silicone oil made it possible to achieve high self-healing efficiency under natural conditions. The coating system not only improved the ice removal ability, but also had excellent water-sliding properties, the droplet could slide under its own weight on 60-PUa at a tilt angle of 4.7°. This work provides an easy way to fabricate multi-functional SLIPS with durability.

A robust antagonistically assembled triboelectric nanogenerator based on dead‐end closed pore through a one‐step improved phase separation

AbstractThe ongoing global energy crisis presents a significant challenge all over the world. In this study, triboelectric nanogenerator (TENG) made of recyclable thermoplastic polycarbonate has been proposed as a promising environmentally friendly solution due to its potential capability to convert low‐frequency mechanical energy sources such as human motion and ocean waves into electricity with potential applications including powering wearable electronic devices and self‐powered sensors. We introduce an antagonistically structured TENG (A‐TENG) composed of honeycomb porous polycarbonate (hc‐PC) and convex‐patterned dimethylsiloxane, employing a novel one‐stage improved phase separation method. This A‐TENG overcomes the demerits of others thanks to its high surface contact area, simplified fabrication process, enhanced energy conversion efficiency, and cost‐effectiveness, requiring minimal investment. More importantly, this work utilized hc‐PC as a framework for slippery liquid‐infused porous surface (SLIPS) based TENG owing to the special honeycomb porous structure to impregnate silicon oil within pore arrays and mechanically support the whole system. The practical application of SLIPS‐TENG was demonstrated while deployed on the house rooftop to harvest raindrop energy and act as a rain detection sensor.

UV-driven self-replenishing liquid-infused surface with promising anti-algal adhesion performance.

Slippery liquid-infused porous surfaces (SLIPSs) inspired by Nepenthes have attracted much attention owing to their potential application in various cutting-edge fields. However, the performance of SLIPSs is impeded by surface damage and lubricant depletion, thereby limiting their further application. Herein, a UV-responsive slippery surface (SMEMG) was fabricated by introducing the UV-responsive functional group coumarin into the polymer side chain through random copolymerization, followed by crosslinking, curing and impregnation with vegetable oil. The self-healing ability and lubricant self-replenishing performance of the SMEMG were investigated. The results show that upon exposure to UV light, the damaged surface substrate can be repaired through a reversible photodimerization reaction between coumarin groups. Meanwhile, the lubricant oil within the bulk of the SMEMG substrate can be extruded to the surface during the photodimerization reaction, facilitating the recovery of surface wettability. The SMEMG exhibited excellent self-cleaning and anti-algal properties as well as durability in a harsh environment, demonstrating its promising application in marine anti-fouling.

Estimation of the Structure of Hydrophobic Surfaces Using the Cassie-Baxter Equation.

The effect of extreme water repellency, called the lotus effect, is caused by the formation of a Cassie-Baxter state in which only a small portion of the wetting liquid droplet is in contact with the surface. The rest of the bottom of the droplet is in contact with air pockets. Instrumental methods are often used to determine the textural features that cause this effect-scanning electron and atomic force microscopies, profilometry, etc. However, this result provides only an accurate texture model, not the actual information about the part of the surface that is wetted by the liquid. Here, we show a practical method for estimating the surface fraction of texture that has contact with liquid in a Cassie-Baxter wetting state. The method is performed using a set of ethanol-water mixtures to determine the contact angle of the textured and chemically equivalent flat surfaces of AlSI 304 steel, 7500 aluminum, and siloxane elastomer. We showed that the system of Cassie-Baxter equations can be solved graphically by the wetting diagrams introduced in this paper, returning a value for the texture surface fraction in contact with a liquid. We anticipate that the demonstrated method will be useful for a direct evaluation of the ability of textures to repel liquids, particularly superhydrophobic and superoleophobic materials, slippery liquid-infused porous surfaces, etc.

Environmentally benign bioinspired oleogel infused surface based on edible sunflower seed oil: Preparation and corrosion mitigating for Mg-Li alloy

The production of metals is an essential process to contribute carbon dioxide emission. Being exposed in natural and industrial environment, metal endures corrosion, which in turn leads to significant material loss. Thus, protecting metal from corrosion is not just a matter of material preservation but also a critical aspect for promoting environmental sustainability. Acting as a barrier, traditional organic coating is widely adopted to prevent metal from corrosion. However, over time, the coating degradation contributes to the growing problem of microplastic pollution. Given these concerns, the challenge lies in developing sustainable, environmentally friendly methods for protecting metals from corrosion. Bioinspired slippery liquid-infused porous surface (SLIPS) has emerged as advantageous solutions for corrosion protection. In this study, firstly, a bioinspired superhydrophobic coating is constructed onto a highly active Magnesium-lithium (Mg-Li) alloy via a one-step electrodeposition. Following that, an edible beeswax-sunflower seed oil is used to form a composite oleogel-infused surface (OIS), one category of SLIPS. Traditional characterization, such as high-resolution transmission electron microscopy (HRTEM), and sophisticated X-ray computed tomography (X-CT) reveal the detailed microstructure and composition of the coatings. The corrosion resistance of OIS surfaces significantly surpasses that of superhydrophobic surfaces, as evaluated by scanning Kelvin probe (SKP), electrochemical impedance spectroscopy, and potentiodynamic polarization curve. The OIS exhibits a high corrosion inhibition efficiency of 99.99%, far exceeding that of the superhydrophobic surface. Furthermore, the OIS demonstrates self-healing capability, with waxy components undergoing phase transition to repair surface damage caused by scratching. This environmentally sustainable biomimetic coating affords versatility and long-term corrosion protection for Mg-Li alloy, paving a new way for their extensive utilization in various fields.

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

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

Pinning Forces on the Omniphobic Dry, Liquid-Infused, and Liquid-Attached Surfaces.

Omniphobic coatings effectively repelling water, oils, and other liquids are of great interest and have a broad number of applications including self-cleaning, anti-icing surfaces, biofouling protection, selective filtration, etc. To create such coatings, one should minimize the pinning force that resists droplet motion and causes contact angle hysteresis. The minimization of the free surface energy by means of the chemical modification of the solid surface is not enough to obtain a nonsticky slippery omniphobic surface. One should minimize the contact between the solid and the droplet. Besides coating the surface with flat polymer films, among the major approaches to create omniphobic coatings, one can reveal "lotus effect" textured coatings, slippery liquid-infused porous surfaces (SLIPS), and slippery omniphobic covalently attached liquid (SOCAL) coatings. It is possible to turn one surface type into other by texturizing, impregnating with liquids, or grafting flexible liquid-like polymer chains. There are a number of models describing the pinning force on surfaces, but the transitions between states with different wetting regimes remain poorly understood. At the same time, such studies can significantly broaden existing ideas about the physics of wetting, help to design coatings, and also contribute to the development of generalized models of the pinning force. Here we review the existing pinning force (contact angle hysteresis) models on various omniphobic substrates. Also, we discuss the current studies of the pinning force in the transitions between different wetting regimes.

Facile fabrication of slippery liquid infused porous surface with self-repairing mesoporous structure and slippery attributes for magnesium alloy corrosion protection

The slippery liquid infused porous surface (SLIPS) with excellent anti-corrosion properties have been widely reported in recent years. Unfortunately, most of the previously reported SLIPS struggles to provide long-term effective corrosion protection for magnesium (Mg) alloys owing to the lack of effective mesoporous structure self-repairing capability. Herein, a SLIPS with a self-repair microstructure and slippery attributes was fabricated, which consisted of a MnOOH layer and a superhydrophobic active carbon/hydroxyl-modified hexagonal boron nitride (AC/BNO) coating. The abundant mesoporous structure of the AC favors the formation of a dense lubricant layer on the SLIPS. The addition of BNO as a two-dimensional filler creates a “labyrinth effect” within SLIPS, which enhances its overall corrosion resistance. In addition, MnOOH offers a self-repair microstructure and slippery attribute ability for SLIPS. Once the SLIPS is damaged, the damaged area undergoes structural and slippery attributes repair through the spontaneous reaction of MnOOH with Mg2+ and OH− to form Mn-Mg layered double hydroxides (LDH) with mesoporous structure for restoration. Moreover, the SLIPS not only exhibited excellent mechanical stability and anti-contamination performance, but electrochemical experiments also indicated that the corrosion protection efficiency of both the original and self-repaired SLIPS was greater than 99 %, demonstrating excellent corrosion resistance. Therefore, compared with traditional SLIPS, this study not only utilizes AC as storage container to avoid the complex mesoporous structure preparation process but also provides new insights for the sustainable development of SLIPS by regenerating new mesoporous structures and restoring the slippery attributes.

Flexible, transparent, and durable slippery liquid‐infused porous surface achieved by void‐centered PVDF‐co‐HFP membrane for self‐cleaning antifog coating

AbstractBioinspired smart surfaces, such as slippery liquid‐infused porous surfaces (SLIPS), have garnered significant attention due to their efficacy in self‐cleaning, antifouling, and antibacterial applications. Despite their advantages, SLIPS exhibit limitations such as compromised transparency, insufficient stability, and limited slippery performance, which have hindered their widespread practical use. To address these challenges, this article proposes a rational design utilizing a void‐centered poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF) membrane for slippery liquid‐infused porous surfaces with exceptional flexibility, transparency, durability, and superior slippery performance. These advancements promise to enhance high‐performance, self‐cleaning, and antifogging coatings. The membranes, featuring large‐area, thickness‐customizable void‐centered PVDF, are fabricated through a two‐step process involving phase separation and selective etching. The utilization of PVDF polymer, which has a refractive index similar to that of silicon‐based lubricant oil, enhances transparency, while macrovoids positioned at the membrane's center, acting as oil reservoirs, improve the stability and performance of the SLIPS surfaces. Experimental findings demonstrate remarkable transparency of up to 93% in the visible light range and a lubricant oil uptake of 2.32 at a porosity of 70%. Moreover, the developed SLIPS exhibit outstanding durability, maintaining slippery performance with sliding angles of <10° following exposure to either 400 consecutive droplets or aging for up to 40 days. This study significantly contributes to the development of future SLIPS, particularly for applications such as antifogging coatings on vehicle glass and solar panels, and self‐cleaning surfaces.

Fabrication of Stable Liquid-like Wetting Buckled Surfaces as Bioinspired Antibiofouling Coatings by Using Silicon-Containing Block Copolymers.

Inspired by animals with a slippery epidermis, durable slippery antibiofouling coatings with liquid-like wetting buckled surfaces are successfully constructed in this study by combining dynamic-interfacial-release-induced buckling with self-assembled silicon-containing diblock copolymer (diBCP). The core diBCP material is polystyrene-block-poly(dimethylsiloxane) (PS-b-PDMS). Because silicon-containing polymers with intrinsic characters of low surface energy, they easily flow over and cover a surface after it has undergone controlled thermal treatment, generating a slippery wetting layer on which can eliminate polar interactions with biomolecules. Additionally, microbuckled patterns result in curved surfaces, which offer fewer points at which organisms can attach to the surface. Different from traditional slippery liquid-infused porous surfaces, the proposed liquid-like PDMS wetting layer, chemically bonded with PS, is stable and slippery but does not flow away. PS-b-PDMS diBCPs with various PDMS volume fractions are studied to compare the influence of PDMS segment length on antibiofouling performance. The surface characteristics of the diBCPs─ease of processing, transparency, and antibiofouling, anti-icing, and self-cleaning abilities─are examined under various conditions. Being able to fabricate ecofriendly silicon-based lubricant layers without needing to use fluorinated compounds and costly material precursors is an advantage in industrial practice.

Industrial and biomedical applications of slippery liquid-infused porous surfaces

Abstract Slippery liquid-infused porous surfaces (SLIPS) are biomimetic interface materials that consist of a porous structure or polymer network substrate with a high specific surface area and a perfused liquid lubricant. This surface has an extremely low coefficient of friction and a high degree of antifouling property, which can effectively repel various liquids, oils, ice, biofilms, etc. The tunable performance of SLIPS endows it with promising application prospects in various fields, thus emphasizing the importance of designing diverse SLIPS materials tailored to specific application scenarios in the future. However, owing to the inherent fluid properties of lubricating oil, the surface may encounter challenges associated with lubricant depletion during practical utilization. This review paper focuses on elucidating the principles, design strategies, and fabrication techniques employed for developing SLIPS materials in anti-ice applications, drag reduction applications, and biomedicine. Furthermore, a comprehensive summary of challenges encountered by SLIPS in different domains is provided along with potential avenues for future research to improve the stability and durability of SLIPS. In conclusion, SLIPS shows significant potential for diverse applications, yet necessitates comprehensive research to address its inherent challenges and extend its versatility and functionality across various domains.