Oil-Infused Superhydrophobic Silicone Material for Low Ice Adhesion with Long-Term Infusion Stability

Adhesion and Contact Aging of Acrylic Pressure-Sensitive Adhesives to Swollen Elastomers

Fluid-infused (or swollen) elastomers are known for their antiadhesive properties. The presence of excess fluid at their surface is the main contributor to limiting contact formation and minimizing adhesion. Despite their potential, the mechanisms for adhesion and contact aging to fluid-infused elastomers are poorly understood beyond contact with a few materials (ice, biofilms, glass). This study reports on adhesion to a model fluid-infused elastomer, poly(dimethylsiloxane) (PDMS), swollen with silicone oil. The effects of oil saturation, contact time, and the opposing surface are investigated. Specifically, adhesion to two different adherents with comparable surface energies but drastically different mechanical properties is investigated: a glass surface and a soft viscoelastic acrylic pressure-sensitive adhesive film (PSA, modulus ∼25 kPa). Adhesion between the PSA and swollen PDMS [with 23% (w/w) silicone oil] retains up to 60% of its value compared to contact with unswollen (dry) PDMS. In contrast, adhesion to glass nearly vanishes in contact with the same swollen elastomer. Adhesion to the PSA also displays stronger contact aging than adhesion to glass. Contact aging with the PSA is comparable for dry and unsaturated PDMS. Moreover, load relaxation when the PSA is in contact with the PDMS does not correlate with contact aging for contact with the dry or unsaturated elastomer, suggesting that contact aging is likely caused by chain interpenetration and polymer reorganization within the contact region. Closer to full saturation of the PDMS with oil, adhesion to the PSA decreases significantly and shows a delay in the onset of contact aging that is weakly correlated to the poroelastic relaxation of the elastomer. Additional confocal imaging suggests that the presence of a layer of fluid trapped at the interface between the two solids could explain the delayed (and limited) contact aging to the oil-saturated PDMS.

Uniformly Hybrid Surface Containing Adjustable Hydrophobic/Hydrophilic Components Obtained by Programmed Strain for Synergistic Anti-Icing

Sufficient efforts have been put into the design of anti-icing materials to eliminate the icing hazard. Among the currently approved anti-icing concepts, hydrophilic/hydrophobic hybrid anti-icing materials inspired by antifreeze proteins show excellent properties in inhibiting ice nucleation, inhibiting ice crystal growth, and reducing ice adhesion. However, it is still a great challenge to accurately regulate the hydrophilic and hydrophobic hybrid components of the coating surface to clarify the synergistic mechanism. This work proposes a strain-manipulated surface modification strategy, and an anti-icing coating with adjustable hydrophilic/hydrophobic hybrid components prepared by combining chemical vapor deposition and siloxane chemistry is obtained. According to the ice resistance experiment at -15 °C, the performance of anti-icing is closely related to the proportion of hydrophilic and hydrophobic hybrids. The icing delay time and ice adhesion strength of the material with the optimal hydrophilic/hydrophobic components are 280 s and 18.6 kPa, respectively. These unique properties can be attributed to the synergistic effect of hydrophilic and hydrophobic structures on the regulation of interfacial water.

Design of a Liquid Impregnated Surface with a Stable Lubricant Layer in a Mixed Water/Oil Environment for Low Hydrate Adhesion

Clathrate hydrate is a naturally occurring icelike solid that forms in the water phase under suitable temperature and pressure conditions in the presence of one or more hydrophobic molecules. It also forms inside the oil and gas pipes, leading to higher pumping cost, flow blockage, and even catastrophic accidents. Engineered surfaces with low hydrate adhesion can provide an effective solution to this problem. Liquid impregnated surfaces are examples of engineered surfaces that have already shown tremendous potential for reducing the nucleation and adhesion of solids. Here, we report the design and synthesis of liquid impregnated surfaces with extremely low hydrate adhesion under an oil and water mixed environment. The most challenging aspect of designing these surfaces was to stabilize a lubricant layer simultaneously under water and oil. A detailed methodology to make such lubricant-stable surfaces from a theoretical perspective was described and experimentally validated for lubricant stability. Experimental measurements on such surfaces showed extremely low hydrate accumulation and 1 order of magnitude or more reduction in hydrate adhesion force.

Anti-Icing Mechanism for a Novel Slippery Aluminum Stranded Conductor

The icing of transmission conductor seriously threatens the safe operation of power grids. Slippery lubricant-infused porous surface (SLIPS) has shown great potential for anti-icing applications. However, aluminum stranded conductors have complex surfaces, and the current SLIPSs are almost prepared and studied on small flat plates. Herein, the construction of SLIPS on the conductor was realized through anodic oxidation and the anti-icing mechanism of the slippery conductor was studied. Compared to the untreated conductor, the SLIPS-conductor reduces the icing weight by 77% in the glaze icing test and shows very low ice-adhesion strength (7.0 kPa). The excellent anti-icing performance of the slippery conductor is attributed to the droplet impact dynamics, icing delay, and lubricant stability. The dynamic behavior of water droplets is most affected by the complex shape of the conductor surface. Specifically, the impact of the droplet on the conductor surface is asymmetric and the droplet can slide along the depression in low-temperature and high-humidity environments. The stable lubricant of SLIPS increases both the nucleation energy barriers and the heat transfer resistance, which greatly delays the freezing time of droplets. Besides, the nanoporous substrate, the compatibility of the substrate with the lubricant, and the lubricant characteristics contribute to the lubricant stability. This work provides theoretical and experimental guidance on anti-icing strategies for transmission lines.

A Slippery Liquid-Infused Network-like Surface with Anti/De-icing Properties Constructed Based on the Phosphating Reaction

The excessive accumulation of ice seriously threatens various industrial facilities and production activities. Currently, slippery liquid-injected porous surfaces (SLIPS) have been developed as a new strategy for anti/de-icing; however, the lack of research on the adsorption and storage capacity for lubricating fluids has limited the development of SLIPS in the anti/de-icing field to some extent. In this work, a slippery liquid-infused phosphate network-like surface (SLIPNS) is prepared that adjusts the texture of the surface by varying the phosphating time to control the adsorption and storage of lubricating fluids. The as-obtained surface structure gives the SLIPNS excellent oil-storage/locked properties, can delay the freezing time of sessile droplets up to 436 s, which is almost 10 times that of an untreated aluminum sheet, and exhibits one-tenth the ice adhesion strength of untreated aluminum substrates (14.39 kPa). In addition, the SLIPNS shows effective durability and antifouling ability and has great potential in solving long-term anti/de-icing problems.

Adhesion of fluid infused silicone elastomer to glass

Elastomers swollen with non-polar fluids show potential as anti-adhesive materials. We study the effect of oil fraction and contact time on the adhesion between swollen spherical probes of PDMS (polydimethylsiloxane) and flat glass surfaces. The PDMS probes are swollen with pre-determined amount of 10 cSt silicone oil to span the range where the PDMS is fluid free (via solvent extraction) up to the limit where it is oil saturated. Probe tack measurements show that adhesion decreases rapidly with an increase in oil fraction. The decrease in adhesion is attributed to excess oil present at the PDMS-air interface. Contact angle measurements and optical microscopy images support this observation. Adhesion also increases with contact time for a given oil fraction. The increase in adhesion with contact time can be interpreted through different competing mechanisms that depend on the oil fraction where the dominant mechanism changes from extracted to fully swollen PDMS. For partially swollen PDMS, we observe that adhesion initially increases because of viscoelastic relaxation and at long times increases because of contact aging. In contrast, adhesion between fully swollen PDMS and glass barely increases over time and is mainly due to capillary forces. While the relaxation of PDMS in contact is well-described by a visco-poroelastic model, we do not see evidence that poroelastic relaxation of the PDMS contributes to an increase of adhesion with glass whether it is partially or fully swollen.

Thermo-responsive Fluorinated Organogels Showing Anti-fouling and Long-Lasting/Repeatable Icephobic Properties

Accumulations of ice on modern infrastructures often cause severe consequences. As such, there is significant interest in developing functional coatings/surfaces that can prevent this. One such approach has been demonstrated with slippery liquid-infused porous surfaces (SLIPS) and organogels where the ice adhesion strength is reduced to the critical point (less than 10 kPa) where it can be removed by natural forces such as gravity, wind, vibrations, and so forth. However, both designs are limited by lubricant depletion. If lubricant release and reabsorption (syneresis) of organogels can be arbitrarily controlled by the surrounding temperature, the loss due to unfavorable evaporation and drainage of infused lubricants can be minimized and its durability can be extended. This study demonstrates the tunable thermo-responsive syneresis of transparent fluorinated organogels (F-ORGs) prepared from a commercial silicone elastomer and a lubricant mixture of fluorinated silicone oil and either poly(dimethylsiloxane) or poly(methylphenylsiloxane). By carefully tuning the ratio of the two lubricants in the mixture, the corresponding F-ORGs demonstrated arbitrarily tunable critical syneresis temperatures from -15 to 40 °C, below which the lubricant is released on the surface and above which the lubricant is re-absorbed. The resulting surfaces showed not only exceptionally long-lasting/repeatable low ice adhesion strengths (≤10 kPa over 50 icing/de-icing cycles) but also significant improvements in their repellency toward a variety of organic liquids. Compared to non-fluorinated organogels, F-ORGs could offer improved protection against outdoor pollutants to further enhance their practicality.

Durable Icephobic Slippery Liquid-Infused Porous Surfaces (SLIPS) Using Flame- and Cold-Spraying

Icing and ice accretion cause severe problems in different industrial sectors, e.g., in aircrafts, aviation traffic, ships, solar panels, and wind turbines. This can lead to enormous economic losses and serious safety issues. Surface engineering can tackle these problems by designing surface structures to work as icephobic coatings and, this way, act as passive anti-icing solutions. In this research, slippery liquid-infused porous structures were fabricated using flame- and cold-spraying to produce polymer (LDPE and PEEK) coatings, and impregnated with a silicone lubricant. Microstructural details, surface properties, wetting behavior, and cyclic icing–deicing behavior were evaluated via ice adhesion measurements, which show the potential performance of SLIPS designs. All these SLIPS showed low or medium-low ice adhesion after the first icing-deicing cycle and the best candidate showed stable performance even after several icing-deicing cycles.

Effect of Polydimethylsiloxane Oil Lubrication on the Friction of Cross-Country UHMWPE Ski Bases on Snow

Silicone oils are known for their excellent lubricating properties, low toxicity and are ice-, snow-, and hydrophobic. With the upcoming ban on fluorine-containing glide products imposed by the International Ski Federation (FIS), novel glide enhancers for skis are desperately needed. Here, the effect of four silicone oil viscosities (10, 20, 50, and 100 cSt) have been evaluated at three temperatures and snow conditions ranging from −10 °C dry snow to +5 °C wet snow. In dry snow conditions, the shear forces introduced by the silicone oil film increased friction significantly compared to a ski without any treatment. On wet snow, the increased hydrophobicity from the silicone oils reduced the friction by 10%. While commercial glide wax outperformed the silicone oils, this study reports the silicone oils do have desirable friction reducing properties for wet conditions.

Mechanically durable anti-bacteria non-fluorinated superhydrophobic sponge for highly efficient and fast microplastic and oil removal

Microplastics (MPs) pollution evolves into a global environmental problem to be solved urgently. Although many studies are exploring ways to remove MPs from water environment, most of them are lack of selectivity and low efficiency. Herein, considering the fascinating absorption selectivity of superwetting materials, a robust magnetic-responsive superhydrophobic and superoleophilic sponge was firstly used to quickly eliminate MPs from water with very high efficiency. The functional sponge was fabricated by a non-fluorinated coating technique that consisted of polydimethylsiloxane (PDMS) grafted Fe₃O₄ particle, PDMS grafted halloysite nanotubes, and PDMS binder. The coated sponge achieved excellent mechanically durable and chemically stable superhydrophobicity that resisted a series of severe treatments. It was unquestionable to show very fast oil absorption. What's more, it especially showed very high adsorption capacity (24.3-48.2 mg/g) and could quickly adsorb almost 100% MPs (polypropylene, polyvinyl chloride, and polyethylene) from aqueous suspensions. Moreover, the removal rates remained almost 100% for these MPs after 50 cycles. Besides, the coated sponge had excellent salt tolerance and antibacterial activity to Escherichia coli (E. coli) (99.91%) and Staphylococcus aureus (S. aureus) (90.46%). The adsorption mechanism of the coating was discussed from the perspectives of molecular structure, electronic effect, steric hindrance, and size-scale effect. The absorption driving force mainly derived from the intra-particle diffusion under capillary attraction, whilst slight electrostatic interaction, hydrogen bond interaction, and σ-p (or p-p) conjugation between PDMS and MPs. This functional sponge was destined to be a new strategy in the removal of MPs and other solid pollutants, especially in the high-salinity and rich-microorganism water environment.

Mechanical Durability of Low Ice Adhesion Polydimethylsiloxane Surfaces

Elastomeric surfaces and oil-infused elastic surfaces reveal low ice adhesion, in part because of their deformability. However, these soft surfaces might jeopardize their mechanical durability. In this work, we analyzed the mechanical durability of elastic polydimethylsiloxane (PDMS) surfaces with different balances between elasticity and deicing performances. The durability was studied in terms of shear/tensile ice adhesion strength before and after different wear tests. These tests consisted of abrasion/erosion cycles using standard procedures aimed to reproduce different environmental wearing agents. The main objective is to evaluate if our PDMS surfaces can become long-lasting solutions for ice removal in real conditions. We found that our elastic surfaces show excellent durability. After the wear tests, the ice adhesion strength values remained low or even unaltered. Although the oil-infused PDMS surface was the softest one, it presented considerable durability and excellent low ice adhesion, being a promising solution.

Overview of the development of slippery surfaces: Lubricants from presence to absence

The superhydrophobic surfaces inspired by the lotus have excellent performances and are known for their low contact angle hysteresis and smooth surfaces. However, there are still some problems, such as the unstable structure, poor durability, high product cost and so on that need to be improved. Those issues can be avoided via liquid-infused surfaces(LIS), which are inspired by Nepenthes and consist of a mico-nano structured substrate and a smooth continuous atomic-grade lubricant. Compared with superhydrophobic surfaces, LIS not only achieves the same hydrophobic properties but also has smaller contact angle hysteresis, smoother surface, more stable structure and lower preparation cost. Although the existence of a lubricant layer improves the performance of the material, it also leaves a hidden danger, which is easy to lose and leads to the deterioration of the durability of the material. Therefore, the lubricant-free slipper materials have attracted more and more attention in recent years due to their low volatility, good durability and excellent lubrication performance. In this review, the types of LIS lubricants and their physicochemical properties were summarized at the beginning and then the applications of LIS in various fields were introduced. At the end of this paper, some solid lubricants and their applications were described, and the future development prospects of LIS lubricants also were expected.

Ice adhesion of PDMS surfaces with balanced elastic and water-repellent properties

HYPOTHESIS

Ice adhesion to rigid materials is reduced with low energy surfaces of high receding contact angles. However, their adhesion strength values are above the threshold value to be considered as icephobic materials. Surface deformability is a promising route to further reduce ice adhesion.

EXPERIMENTS

In this work, we prepared elastomer surfaces with a wide range of elastic moduli and hydrophobicity degree and we measured their ice adhesion strength. Moreover, we also explored the deicing performance of oil-infused elastomeric surfaces. The ice adhesion was characterized by two detachment modes: tensile and shear.

FINDINGS

The variety of elastomeric surfaces allowed us to simultaneously analyze the ice adhesion dependence with deformability and contact angle hysteresis. We found that the impact of these properties depends on the detachment mode, being deformability more important in shear mode and hydrophobicity more relevant in tensile mode. In addition, oil infusion further reduces ice adhesion due to the interfacial slippage. From an optimal balance between deformability and hydrophobicity, we were able to identify surfaces with super-low ice adhesion.

Ice-Shedding Polymer Coatings with High Hardness but Low Ice Adhesion

Ice readily sheds from weak oil-swollen polymer gels but tends to adhere to mechanically robust coatings. This paper reports bilayer coatings that simultaneously possess high bulk hardness but low ice adhesion. These coatings are prepared by cocuring a triisocyanate, P#'-g-PDMS [a methacrylate polyol bearing poly(dimethylsiloxane) (PDMS) side chains with # being 1, 2, or 3 and g denoting graft], and optionally a methacrylate polyol P#. The self-assembly of the system during coating formation yields a PDMS brush layer on the surface of the cross-linked polyurethane matrix. After the surface PDMS layer is lubricated with a silicone oil, this coating exhibits an ice adhesion τ that is 10 000-fold lower than that of a triisocyanate/P# coating. Ice slides under its own weight on such a coating at a tilt angle of 3°. Yet, the coating matrix is harder than poly(ethylene terephthalate), a widely used plastic. Additionally, such a coating maintains its low τ values for more than 10 consecutive icing/deicing cycles. Subsequent increases in τ are reversed by allowing time for the replenishment of the depleted surface lubricant with that released from the coating matrix. This design opens the door for effective yet hard ice-shedding polymer coatings.

Multifunctional Slippery Polydimethylsiloxane/Carbon Nanotube Composite Strain Sensor with Excellent Liquid Repellence and Anti-Icing/Deicing Performance

In this paper, a multifunctional slippery polydimethylsiloxane/carbon nanotube composite strain sensor (SPCCSS) is prepared using a facile template method. Benefitting from the slippery surface, the SPCCSS shows excellent liquid repellence properties, which can repel various liquids such as oil, cola, yogurt, hot water and some organic solvents. Meanwhile, the SPCCSS has a large strain sensing range (up to 100%), good sensitivity (GF = 3.3) and stable response with 500 cyclic stretches under 20% strain. Moreover, it is also demonstrated that the SPCCSS displays outstanding corrosion resistance (from pH = 1 to pH = 14) and anti-icing (8 min at −20 °C)/photothermal deicing (104 s with NIR power density of 1 W/cm²) properties, broadening its application in extreme acid, alkali and low-temperature conditions. Therefore, the multifunctional SPCCSS with the liquid repellence, anti-corrosion, and anti-icing/deicing properties has potential applications in wearable human motion monitoring tools under complex harsh environments.

Enhanced Surface Icephobicity on an Elastic Substrate

Ice accumulation on exposed surfaces is unavoidable as time elapses and the temperature decreases sufficiently. To mitigate icing problems, various types of icephobic substrates have been rationally designed, including superhydrophobic substrates (SHSs), aqueous lubricating layers, organic lubricating layers, organogels, polyelectrolyte brush layers, electrolyte-based hydrogels, elastic substrates, and multicrack initiator-promoted surfaces. Among these surfaces, elastic substrates show excellent enhanced surface icephobicity during dynamic processes (i.e., water-impacting and de-icing tests). Herein, we summarize recent progress in elastic icephobic substrates and discuss the reasons that surface icephobicity can be enhanced on elastic substrates in terms of enhanced water repellency and further lowering the ice adhesion strength. For enhanced water repellency, we focus on reducing the contact time of water impacting such that water droplets can be easily shed from an elastic substrate before ice occurs. Reducing the contact time of water impacting various substrates (i.e., micro/nanostructured rigid SHSs, macrotextured rigid SHSs, and elastic SHSs) is discussed, followed by exploring their mechanisms. We argue that the ice adhesion strength can be further lowered on an elastic substrate by rationally tuning the elastic modulus and surface textures (i.e., surface textured and hollow subsurface textured) and combining elastic substrate with other passive anti-icing strategies (or functioning passive icephobic substrates with an electrothermal or photothermal stimulus). In short, the introduction of an elastic substrate into a passive or active icephobicity surface opens an avenue toward designing a versatile icephobic surface, providing great potential for outdoor anti-icing applications.

Design of Icephobic Surfaces by Lowering Ice Adhesion Strength: A Mini Review

Ice accretion can lead to severe consequences in daily life and sometimes catastrophic events. To mitigate the hazard of icing, passive icephobic surfaces have drawn widespread attentions because of their abilities in repelling incoming water droplets, suppressing ice nucleation and/or lowering ice adhesion strength. As time elapses and temperature lowers sufficiently, ice accretion becomes inevitable, and a realistic roadmap to surface icephobicity for various outdoor anti-icing applications is to live with ice but with the lowest ice adhesion strength. In this review, surfaces with icephobicity are critically categorized into smooth surfaces, textured surfaces, slippery surfaces and sub-surface textured surfaces, and discussed in terms of theoretical limit, current status and perspectives. Particular attention is paid to multiple passive anti-icing strategies combined approaches as proposed on the basis of icephobic surfaces. Correlating the current strategies with one another will promote understanding of the key parameters in lowering ice adhesion strength. Finally, we provide remarks on the rational design of state-of-the-art icephobic surfaces with low ice adhesion strength.

Nature-inspired slippery polymer thin film for ice-repellent applications

In this study, the authors investigated the anti-icing performance of a hierarchical slippery polymer thin film that is inspired by structures of the lotus leaf and Nepenthes pitcher plant. The polymer solution was mixed with the lubricant at the appropriate concentration to achieve slippery properties. The dry etching method followed by the spin-coating process was used to generate a uniform polymer microstructure on the thin film. The polymer nanostructure was then yielded by an additional plasma-etching method using carbon tetrafluoride (CF4) gas. The anti-icing efficiency was then compared with that of the non-functional samples to demonstrate the advantages of combination in all criteria. Moreover, a theoretical prediction based on the free-energy approach was used to measure the nucleation time at the interface and illustrated good agreement with real-time measurement. The results propose a new and facile approach for outdoor anti-icing applications.

Recent Progress of Bioinspired Scalephobic Surfaces with Specific Barrier Layers

Bioinspired superwettable surfaces have been widely harnessed in diverse applications such as self-cleaning, oil/water separation, and liquid transport. So far, only a little work is focused on scalephobic capability of those superwettable surfaces. However, the troublesome scale deposition will inevitably be observed in our daily production and life, greatly reducing heat transfer efficiency and inhibiting the liquid transport. To address this annoying problem, as the emerging strategy, specific barrier layers are introduced onto superwettable surfaces to reduce or even avoid the direct contact between scale and the surfaces. In this feature article, we first provide the basic concept of bioinspired scalephobic surfaces with specific barrier layers. Then, we briefly introduce the typical fabrication methods of scalephobic surfaces. Later, we summarize recent progress of bioinspired scalephobic surfaces with specific barrier layers. Furthermore, we point out the guiding theory and criteria for the stability of barrier layers. Finally, we put forward the forecast on the existing problems and future direction in bioinspired scalephobic surfaces.

Contact line relaxation of sessile drops on PDMS surfaces: A methodological perspective

HYPOTHESIS

Characterization of contact angle hysteresis on soft surfaces is sensitive to the measurement protocol and might present adventitious time-dependencies. Contact line dynamics on solid surfaces is altered by the surface chemistry, surface roughness and/or surface elasticity. We observed a "slow" spontaneous relaxation of static water sessile drops placed on elastic surfaces. This unexpected drop motion reveals unresolved equilibrium configurations that may affect the observed values of contact angle hysteresis. Drop relaxation on deformable surfaces is partially governed by a viscoelastic dissipation located at the contact line.

EXPERIMENTS

In this work, we studied the natural relaxation of water drops formed on several smooth PDMS surfaces with different elastic moduli. We monitored in time the contact angle and contact radius of each drop. For varying the initial contact angle, we used the growing-shrinking drop method.

FINDINGS

We postulate that the so-called "braking effect", produced by the surface deformability, affects the contact line velocity and in consequence, the contact angle measurements. We conclude that the wetting properties of elastic surfaces should be properly examined with reliable values of contact angle measured after drop relaxation.

Slippery liquid infused porous surfaces with corrosion resistance potential on aluminum alloy

The slippery liquid infused porous surface has developed into a potential technology to solve the problem of poor durability in corrosion resistance. Herein, a kind of slippery liquid infused porous surface is created on 7075 aluminum alloy by wire electrical discharge machining for corrosion resistant applications. The hardness of the constructed porous microstructure is similar to the aluminum alloy substrate material, which ensures the stability of the slippery liquid infused porous surface. The modification of low surface energy substance fluorosilane avoids the direct contact between corrosive liquid and porous surface, and improves the lyophobic performance of the porous microstructure surface. The corrosion resistance of the porous microstructure surface is enhanced by the injection of perfluorinated lubricating oil. The experimental results show that the created slippery liquid infused porous surface can display super-slippery properties and durable corrosion resistance. The average sliding velocity of a water droplet is 0.48 ± 0.05 mm s⁻¹ at a sliding angle of 5°. The corrosion current density of the surface is 3.116 × 10⁻⁶ A cm⁻², which is 2 orders of magnitude lower than that of the polished surface. And the impedance radius reaches 90 kΩ cm², which is about 20 times that of the polished surface.

The slippery liquid infused porous surface has developed into a potential technology to solve the problem of poor durability in corrosion resistance.

Robust Photothermal Coating Strategy for Efficient Ice Removal

Preventing ice formation and ice swift removal from the solid surface are essential in numerous application fields. Superhydrophobic coating is an effective way to delay the icing phenomenon. However, the superhydrophobic coating was wetted easily after icing-deicing cycles that led to the failure of anti-icing. In this study, a robust, amphiphobic coating consisted of fluorinated multiwalled carbon nanotubes (FMWCNTs) and commercial polyurethane was constructed by a simply spray process. Because of the addition of FMWCNTs, the coating demonstrated a good amphiphobic feature and highly efficient photothermal conversion, which endowed the coating surface with excellent deicing and defrosting characteristics under sunlight irradiation. In addition, self-cleaning and self-healing properties of the coating under sunlight ensured its efficient photothermal conversion and long service life. To further improve the photothermal deicing effect, a coating system containing a photothermal layer (P), thermal-conductive layer (C), and thermal-protective layer (P) was constructed. The heat generating from the photothermal layer can transfer the whole coating surface by the conductive layer, but with limited transmission to substrate materials by a thermal-protective layer. The coating system can still deice and defrost rapidly on the whole surface and only a small portion of photothermal coating was irradiated under extremely low temperature. The outdoor experiment has confirmed that the coating melted and removed snow rapidly in a winter environment. The multifunctional photothermal deicing coating may have a wide application in outdoor surrounding.

Fabrication of a Porous Slippery Icephobic Surface and Effect of Lubricant Viscosity on Anti-Icing Properties and Durability

A breakdown caused by the icing of power generation infrastructure is one of the serious disasters occurring in the power system. Slippery lubricant-infused porous surfaces (SLIPSs), whose ice adhesion strength is extremely low, have a promising application in the anti-icing field. In the present study, we fabricated SLIPSs with low ice adhesion strength by infusing silicone oil into an anodic aluminum oxide (AAO) substrate. In addition, the effects of the viscosity of silicone oil on the anti-icing properties and durability of the SLIPSs were investigated. The results show that a lower viscosity silicone oil brings about more slippery surfaces and lower ice adhesion strength. The ice adhesion strength was reduced by 99.3% in comparison with the bare Al alloy. However, low-viscosity silicone oil has worse de-icing resistance and heat resistance. Additionally, the porous films filled with low-viscosity silicone oil possess a better self-healing property after icing/de-icing cycles and followed by exposure to the atmosphere. When the viscosity of silicone oil is 50 mPa·s, the SLIPSs exhibit the best durability for anti-icing. Even after 21 de-icing tests or 168 h of heating at 90 °C, the ice adhesion strength still remains below 10% compared with that of bare Al. This work provides some useful advice for the design and fabrication of anti-icing SLIPSs.

Robust Slippery Liquid-Infused Porous Network Surfaces for Enhanced Anti-icing/Deicing Performance

Slippery liquid-infused porous surfaces (SLIPSs) have recently been intensively investigated because of promising potential in various applications that require water repellency. However, the use of SLIPS is limited by its unsatisfactory oil-storage and -replacement capabilities. Here we designed network surface structures with interconnected microchannels and cross-linked nanosheets, which acted as natural oil reservoirs and vessels. A lubricant can be firmly locked and stored into the networks, leading to an efficient water repellency as well as improved mechanical durability and stability. We further show the surface structures can be applied to anti-icing/deicing, demonstrated by its improved icing-delaying, anti-icing, and deicing properties even after multiple cycles, compared to those on superhydrophobic surfaces (SHSs) and the conventional SLIPSs. We envision that this unique design of the slippery liquid-infused porous network surface (SLIPNS) with robust stability and durability may expand its application in extreme environments.

Effect of Ageing on the Structure and Properties of Model Liquid-Infused Surfaces

Liquid-infused surfaces (LISs) exhibit unique properties that make them ideal candidates for a wide range of applications, from antifouling and anti-icing coatings to self-healing surfaces and controlled wetting. However, when exposed to realistic environmental conditions, LISs tend to age and progressively lose their desirable properties, potentially compromising their application. The associated ageing mechanisms are still poorly understood, and results reflecting real-life applications are scarce. Here, we track the ageing of a model LIS composed of glass surfaces functionalized with hydrophobic nanoparticles and infused with silicone oil. The LISs are fully submerged in aqueous solutions and exposed to acoustic pressure waves for set time intervals. The ageing is monitored by periodic measurements of the LIS's wetting properties. We also track the changes to the LIS's nanoscale structure. We find that the LISs rapidly lose their slippery properties because of a combination of oil loss, smoothing of the nanoporous functional layer, and substrate degradation when directly exposed to the solution. The oil loss is consistent with water microdroplets entering the oil layer and displacing oil away from the surface. These mechanisms are general and could play a role in the ageing of most LISs.

Icephobic, Pt-Cured, Polydimethylsiloxane Nanocomposite Coatings

To explore novel coatings with potential for easy release of ice (icephobicity), a series of platinum-cured silicone coatings was prepared incorporating SYL-OFF 7210, designated MQ-R, as a nanoscale reinforcing component. These optically transparent coatings are designated according to cure temperature and MQ-R wt %, for example, Pt-PDMS(25)-20 for 25 °C cure and 20 wt % MQ-R. Surface characterization included dynamic contact angles and morphology by atomic force microscopy. Bulk characterization was accomplished with stress-strain measurements at 25 °C and dynamic mechanical analysis from -110 to 150 °C. Ice adhesion tests at -10 °C showed modulus had a dominant effect in increasing τ_ice, the peak removal force. At -30 °C, storage modulus was greater for coatings cured at 100 °C compared to 25 °C, but ice removal tests at -30 °C (-22 °F) consistently showed τ_ice for Pt-PDMS(100) MQ-R compositions was less than τ_ice for corresponding Pt-PDMS(25) coatings. This unexpected result was explained by proposing that supercooled water at hydrophilic interfacial sites (-10 °C) does not impede ice removal but frozen water pins ice at -30 °C. Interestingly, MQ-R was found to be a reactive filler that increased modulus after 100 °C cure especially for Pt-PDMS(100)-30 (3 MPa) and Pt-PDMS(100)-40 (5 MPa). In summary, by virtue of resistance to ice adhesion Pt(PDMS) coatings with low MQ-R content have potential for conferring energy savings and safety while high MQ-R content results in noteworthy mechanical properties.

Life and death of liquid-infused surfaces: a review on the choice, analysis and fate of the infused liquid layer

We review the rational choice, the analysis, the depletion and the properties imparted by the liquid layer in liquid-infused surfaces – a new class of low-adhesion surface.

Liquid infused surfaces with anti-icing properties

Ice accretion on solid surfaces, a ubiquitous phenomenon that occurs in winter, brings much inconvenience to daily life and can even cause serious catastrophes. Icephobic surfaces, a passive way of processing surfaces to prevent surface destruction from ice accumulation, have attracted much attention from scientists because of their special ice-repellent properties, and many efforts have been made to rationally design durable icephobic coatings. This review is aimed at providing a brief and crucial overview of ice formation processes and feasible de-icing strategies. Here, the excellent anti-icing performance of liquid infused surfaces (LIS) inspired from Nepenthes is emphatically introduced. After a short introduction, the recent progresses in ice nucleation theory and ice adhesion decrease mechanism are comprehensively reviewed to gain a general understanding of the long freeze process and low ice adhesion on LIS. Subsequently, the anti-icing performance of LIS is systematically evaluated from four aspects regarding water repellence, condensation-frosting, long freeze process, and low ice adhesion. Finally, this review focuses on discussing the advantages and disadvantages of LIS and the potential measures to eliminate and alleviate these drawbacks.

Droplet Morphology and Mobility on Lubricant-Impregnated Surfaces: A Molecular Dynamics Study

Slippery liquid-infused porous surfaces (SLIPS) are gaining remarkable attention and have advanced performance in many fields. Although all SLIPS are related to lubricant-impregnation within nano/microstructures on a surface, they differ in many aspects, such as the morphology of droplets, the state of cloaking, the wetting edge, and the lubricant thickness. Requirements of the droplet morphology on SLIPS might change according to a specific application. A molecular-dynamics-based numerical model that can correctly simulate SLIPS is developed and is validated by comparing against the theoretical predictions for all possible stable states for a given droplet, lubricant, and solid surface. On the basis of this model, a detailed analysis of the equilibrium states is conducted. In particular, we discover that the four possible stable states on SLIPS predicted by theoretical studies can be extended to eight states by considering the effects of lubricant thickness and surface geometry in addition to the interfacial tension and surface wettability. These findings could be used to determine the conditions under which a thermodynamically stable state exists on SLIPS. The dynamic behavior of a nanodroplet on SLIPS is also studied, which provides insight into how a proper increase in the lubricant thickness might increase the sliding velocity. The above findings and developed model are expected to provide significant guidelines for designing SLIPS.

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

HYPOTHESIS

State-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.

EXPERIMENTS

Durable 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.

FINDINGS

LISSs 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.

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.

Liquid-Infused Surfaces: A Review of Theory, Design, and Applications

Due to inspiration from the Nepenthes pitcher plant, a frontier of devices has emerged with unmatched capabilities. Liquid-infused surfaces (LISs), particularly known for their liquid-repelling behavior under low tilting angles (<5°), have demonstrated a plethora of applications in medical, marine, energy, industrial, and environmental materials. This review presents recent developments of LIS technology and its prospective to define the future direction of this technology in solving tomorrow's real-life challenges. First, an introduction to the different models explaining the physical phenomena of these surfaces, their wettability, and viscous-dependent frictional forces is discussed. Then, an outline of different emerging strategies required to fabricate a stable liquid-infused interface is presented, including different substrates, lubricants, surface chemistries, and design parameters which can be tuned depending on the application. Furthermore, applications of LIS coatings in the areas of anticorrosion, antifouling, anti-icing, self-healing, droplet manipulation, and biomedical devices will be presented followed by the limitations and future direction of this technology.

Combining the geometry of folded paper with liquid-infused polymer surfaces to concentrate and localize bacterial solutions

Point-of-care (POC) detection and diagnostic platforms provide critical information about health and safety conditions in austere and resource-limited settings in which medical, military, and disaster relief operations are conducted. In this work, low-cost paper materials commonly used in POC devices are coated with liquid-infused polymer surfaces and folded to produce geometries that precisely localize complex liquid samples undergoing concentration by evaporation. Liquid-infused polymer surfaces were fabricated by infusing silicone-coated paper with a chemically compatible polydimethylsiloxane oil to create a liquid overlayer. Tests on these surfaces showed no remaining bacterial cells after exposure to a sliding droplet containing a concentrated solution of Escherichia coli or Staphylococcus aureus, while samples without a liquid layer showed adhesion of both microdroplets and individual bacterial cells. Folding of the paper substrates with liquid-infused polymer surfaces into several functional 3D geometries enabled a clean separation and simultaneous concentration of a liquid containing rhodamine dye into discrete, predefined locations. When used with bacteria, which are known for their ability to adhere to nearly any surface type, functional geometries with liquid-infused polymer surfaces concentrated the cells at levels significantly higher than geometries with dry control surfaces. These results show the potential of synergistically combining paper-based materials with liquid-infused polymer surfaces for the manipulation and handling of complex samples, which may help the future engineering of POC devices.

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.

Influence of long-range forces and capillarity on the function of underwater superoleophobic wrinkled surfaces

Underwater superoleophobic surfaces can be considered a particular type of lubricant-infused surface, that have anti-fouling properties by virtue of a trapped water layer that repels oils. However, as their function relies on a water layer being trapped in the surface roughness, it is crucial to understand the factors that determine the layer stability. In this work, the forces that are responsible for the stability of thin liquid films within structured surfaces were quantified, and the conclusions were tested against the performance of wrinkled surfaces as underwater superoleophobic coatings. Here, the system studied was a family of wrinkled surfaces made of hydrophilic poly(4-vinylpyridine) (P4VP), whereby the wrinkle width could be controllably tuned in the range 90 nm to 8000 nm. The van der Waals free energy was quantified and the capillary forces trapping water in the surface micro- and nano-wrinkle structure were estimated. P4VP surfaces with micro-scale wrinkles had underwater superoleophobic properties, and low adhesion to different oils with droplet roll-off angle below 6° ± 1°. Despite the van der Waals free energy of the system pointing to the dewetting of a water film under oil on top of a smooth P4VP film, the wrinkled structure is sufficient to induce a Cassie state with a trapped water layer. The micro-scale wrinkles (average width 4-12 μm) were found to be particularly effective in the trapping of the water in a Cassie non-adhesive state. The P4VP wrinkled surfaces are superamphiphobic, as when they were first infused with oil, and then exposed to a droplet of water under oil, they exhibited superhydrophobic behavior. The P4VP wrinkles have the additional useful feature of being transparent underwater, which makes them useful candidates for the protection of underwater cameras and sensors.

Directional Passive Transport of Microdroplets in Oil-Infused Diverging Channels for Effective Condensate Removal

Condensation widely exists in nature and industry, and its performance heavily relies on the efficiency of condensate removal. Recent advances in micro-/nanoscale surface engineering enable condensing droplet removal from solid surfaces without extra energy cost, but it is still challenging to achieve passive transport of microdroplets over long distances along horizontal surfaces. The mobility of these condensate droplets can be enhanced by lubricant oil infusion on flat surfaces and frequent coalescence, which lead to fast growth but random motion of droplets. In this work, we propose a novel design of diverging microchannels with oil-infused surfaces to achieve controllable, long-distance, and directional transport of condensing droplets on horizontal surfaces. This idea is experimentally demonstrated with diverging copper and silicon microchannels with nanoengineered surfaces. Along these hierarchical surface structures, microdroplets condense on the top channel wall and submerge into microchannels owing to the capillary pressure gradient in infusing oil. Confined by the microchannel walls, the submerged droplets deform and maintain the back-front curvature difference, which enables the motion of droplets along the channel diverging direction. Subsequent droplet coalescences inside the channel further enhance this directional transport. Moreover, fast-moving deformed droplets transfer their momentum to downstream spherical droplets through the infusing oil. As a result, simultaneous passive transport of multiple droplets (20-400 μm) is achieved over long distances (beyond 7 mm). On these oil-infused surfaces, satellite microdroplets can further nucleate and grow on an oil-cloaked droplet, demonstrating an enlarged surface area for condensation. Our findings on passive condensate removal offer great opportunities in condensation enhancement, self-cleaning, and other applications requiring directional droplet transport along horizontal surfaces.