Hydrophobic Solid Photothermal Slippery Surfaces with Rapid Self-repairing, Dual Anti-icing/Deicing, and Excellent Stability Based on Paraffin and Etching

Ice and snow disasters have greatly affected both the global economy and human life, and the search for efficient and stable anti-icing/deicing coatings has become the main goal of much research. Currently, the development and application of anti-icing/deicing coatings are severely limited due to their complex preparation, structural fragility, and low stability. This work presents a method for preparing hydrophobic solid photothermal slippery surfaces (SPSS) that exhibit rapid self-repairing, dual anti-icing/deicing properties, and remarkable stability. A photothermal layer of copper oxide (CuO) was prepared by using chemical deposition and etching techniques. The layer was then impregnated with stearic acid and solid paraffin wax to create a hydrophobic solid photothermal slippery surface. This solves the issue of low stability on superhydrophobic surfaces caused by fragile and irretrievable micro/nanostructures. In addition, the underlying photothermal superhydrophobic surface provides good anti-icing/deicing properties even if the paraffin on the surface evaporates or is lost during operation. The findings indicate that when subjected to simulated light irradiation, the coating's surface temperature increases to 80 °C within 12 min. The self-repair process is completed rapidly in 170 s, and at -15 °C, it takes only 201 s for the ice on the surface to melt completely. The surface underneath the paraffin exhibited good superhydrophobic properties, with a contact angle (CA) of 154.1° and a sliding angle (SA) of 6.8° after the loss of paraffin. Simultaneously, the surface's mechanical stability and durability, along with its self-cleaning and antifouling properties, enhance its service life. These characteristics provide promising opportunities for practical applications that require long-term anti-icing/deicing surfaces.

Visualization and Experimental Characterization of Wrapping Layer Using Planar Laser-Induced Fluorescence

Droplets on nanotextured oil-impregnated surfaces have high mobility due to record-low contact angle hysteresis (∼1-3°), attributed to the absence of solid-liquid contact. Past studies have utilized the ultralow droplet adhesion on these surfaces to improve condensation, reduce hydrodynamic drag, and inhibit biofouling. Despite their promising utility, oil-impregnated surfaces are not fully embraced by industry because of the concern for lubricant depletion, the source of which has not been adequately studied. Here, we use planar laser-induced fluorescence (PLIF) to not only visualize the oil layer encapsulating the droplet (aka wrapping layer) but also measure its thickness since the wrapping layer contributes to lubricant depletion. Our PLIF visualization and experiments show that (a) due to the imbalance of interfacial forces at the three-phase contact line, silicone oil forms a wrapping layer on the outer surface of water droplets, (b) the thickness of the wrapping layer is nonuniform both in space and time, and (c) the time-average thickness of the wrapping layer is ∼50 ± 10 nm, a result that compares favorably with our scaling analysis (∼50 nm), which balances the curvature-induced capillary force with the intermolecular van der Waals forces. Our experiments show that, unlike silicone oil, mineral oil does not form a wrapping layer, an observation that can be exploited to mitigate oil depletion of nanotextured oil-impregnated surfaces. Besides advancing our mechanistic understanding of the wrapping oil layer dynamics, the insights gained from this work can be used to quantify the lubricant depletion rate by pendant droplets in dropwise condensation and water harvesting.

On the Durability of Icephobic Coatings: A Review

Ice formation and accumulation on surfaces has a negative impact in many different sectors and can even represent a potential danger. In this review, the latest advances and trends in icephobic coatings focusing on the importance of their durability are discussed, in an attempt to pave the roadmap from the lab to engineering applications. An icephobic material is expected to lower the ice adhesion strength, delay freezing time or temperature, promote the bouncing of a supercooled drop at subzero temperatures and/or reduce the ice accretion rate. To better understand what is more important for specific icing conditions, the different types of ice that can be formed in nature are summarized. Similarly, the alternative methods to evaluate the durability are reviewed, as this is key to properly selecting the method and parameters to ensure the coating is durable enough for a given application. Finally, the different types of icephobic surfaces available to date are considered, highlighting the strategies to enhance their durability, as this is the factor limiting the commercial applicability of icephobic coatings.

Innovative Solid Slippery Coating: Uniting Mechanical Durability, Optical Transparency, Anti-Icing, and Anti-Graffiti Traits

Slippery coatings, such as the slippery liquid-infused porous surface (SLIPS), have gained significant attention for their potential applications in anti-icing and anti-fouling. However, they lack durability when subjected to mechanical impact. In this study, we have developed a robust slippery coating by blending polyurethane acrylate (PUA) with methyltriethoxysilane (MTES) and perfluoropolyether (PFPE) in the solvent of butyl acetate. The resulting mixture is homogeneous and allows for uniform coating on various substrates using a drop coating process followed by drying at 160 °C for 3 h. The cured coating exhibits excellent water repellency (contact angle of ~108° and sliding angle of ~8°), high transparency (average visible transmittance of ~90%), exceptional adherence to the substrate (5B rating according to ASTMD 3359), and remarkable hardness (4H on the pencil hardness scale). Moreover, the coating is quite flexible and can be folded without affecting its wettability. The robustness of the coating is evident in its ability to maintain a sliding angle below 25° even when subjected to abrasion, water jetting, high temperature, and UV irradiation. Due to its excellent nonwetting properties, the coating can be employed in anti-icing, anti-graffiti, and anti-sticking applications. It effectively reduces ice adhesion on aluminum substrates from approximately 217 kPa to 12 kPa. Even after 20 cycles of icing and de-icing, there is only a slight increase in ice adhesion, stabilizing at 40 kPa. The coating can resist graffiti for up to 400 cycles of writing with an oily marker pen and erasing with a tissue. Additionally, the coating allows for easy removal of 3M tape thereon without leaving any residue.

Bio-inspired microfluidics: A review

Biomicrofluidics, a subdomain of microfluidics, has been inspired by several ideas from nature. However, while the basic inspiration for the same may be drawn from the living world, the translation of all relevant essential functionalities to an artificially engineered framework does not remain trivial. Here, we review the recent progress in bio-inspired microfluidic systems via harnessing the integration of experimental and simulation tools delving into the interface of engineering and biology. Development of "on-chip" technologies as well as their multifarious applications is subsequently discussed, accompanying the relevant advancements in materials and fabrication technology. Pointers toward new directions in research, including an amalgamated fusion of data-driven modeling (such as artificial intelligence and machine learning) and physics-based paradigm, to come up with a human physiological replica on a synthetic bio-chip with due accounting of personalized features, are suggested. These are likely to facilitate physiologically replicating disease modeling on an artificially engineered biochip as well as advance drug development and screening in an expedited route with the minimization of animal and human trials.

Interdependence of Surface Roughness on Icephobic Performance: A Review

Ice protection techniques have attracted significant interest, notably in aerospace and wind energy applications. However, the current solutions are mostly costly and inconvenient due to energy-intensive and environmental concerns. One of the appealing strategies is the use of passive icephobicity, in the form of coatings, which is induced by means of several material strategies, such as hydrophobicity, surface texturing, surface elasticity, and the physical infusion of ice-depressing liquids, etc. In this review, surface-roughness-related icephobicity is critically discussed to understand the challenges and the role of roughness, especially on superhydrophobic surfaces. Surface roughness as an intrinsic, independent surface property for anti-icing and de-icing performance is also debated, and their interdependence is explained using the related physical mechanisms and thermodynamics of ice nucleation. Furthermore, the role of surface roughness in the case of elastomeric or low-modulus polymeric coatings, which typically instigate an easy release of ice, is examined. In addition to material-centric approaches, the influence of surface roughness in de-icing evaluation is also explored, and a comparative assessment is conducted to understand the testing sensitivity to various surface characteristics. This review exemplifies that surface roughness plays a crucial role in incorporating and maintaining icephobic performance and is intrinsically interlinked with other surface-induced icephobicity strategies, including superhydrophobicity and elastomeric surfaces. Furthermore, the de-icing evaluation methods also appear to be roughness sensitive in a certain range, indicating a dominant role of mechanically interlocked ice.

Photo-Thermal Superhydrophobic Sponge for Highly Efficient Anti-Icing and De-Icing

Ice accretion always brings much inconvenience in the field of production and life. How to anti-ice or de-ice easily on solid surfaces becomes research focus in the engineering material fields. In this work, a kind of photo-thermal superhydrophobic polyurethane sponge (PSP-SPONGE) was developed by depositing Fe₃O₄ nanoparticles and polydopamine and simple fluorination treatment to realize anti-icing and de-icing fast under faint sunlight irradiation. Utilizing the thermal insulation of porous PSP-SPONGE, the photo-thermal energy was located at the sunlight irradiation area, which heated PSP-SPONGE surface rapidly under sunlight irradiation in cold surroundings. Water droplets on PSP-SPONGE surface would never freeze under faint 0.3 kW/m² ("0.3 sun") sunlight illumination in -30 °C damp surroundings, and the ice melts entirely within 18 min under "1 sun" illumination. Furthermore, PSP-SPONGE has excellent self-cleaning and self-healing properties that can cope with the complex and volatile natural environment to guarantee durable anti-icing and de-icing performances. The simulated outdoor snow removal test also proved that snow on PSP-SPONGE surface could melt under "0.5 sun" sunlight illumination in -30 °C damp surroundings. The PSP-SPONGE fabricated with simple preparation and easy access has wide application prospects in anti-icing and de-icing.

Hydro- and Icephobic Properties and Durability of Epoxy Gelcoat Modified with Double-Functionalized Polysiloxanes

Anti-icing coatings have provided a very good alternative to current, uneconomic, active deicing methods, and their use would bring a number of significant benefits to many industries, such as aviation and energy. Some of the most promising icephobic surfaces are those with hydrophobic properties. However, the relationship between hydrophobicity and low ice adhesion is not yet clearly defined. In this work, chemical modification of an epoxy gelcoat with chemical modifiers from the group of double organofunctionalized polysiloxanes (generally called multifunctionalized organosilicon compounds (MFSCs)) was applied. The anti-icing properties of manufactured coatings were determined by means of measurements of shear strength between the ice layer and the modified surface, conducted using a tensile machine. In the work, tests were also performed on the roughness, wettability, and durability of the properties in an aging chamber. It was found that the performed modifications of the coating's chemical composition by the addition of polysiloxanes enabled us to reduce ice adhesion by 51% and to increase the water contact angle by 14% in comparison to the neat gelcoat. A reduction in ice adhesion was also observed with the increasing water contact angle and with decreasing surface roughness. In addition, only one modification recorded an increase in ice adhesion after exposure in the aging chamber.

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.

Effective Icephobicity of Silicone Oil-Infused Oleamide-Polydimethylsiloxane with Enhanced Lubrication Lifetime

Icing and freezing phenomena in cold weather cause serious damage and economic losses. Thus, the development of a new effective icephobic surface with low ice adhesion strength (τ_ice) that can easily remove ice by wind or gravity force is essentially required. In this study, we propose a silicone oil-infused oleamide-polydimethylsiloxane (SiOP) by a facile fabrication method to achieve the effective icephobic performance with enhanced lubrication lifetime. The proposed SiOP is composed of a composite containing oleamide and polydimethylsiloxane (PDMS) and silicone oil impregnated into the polymeric networks of the composite. Oleamide has been used as a slip agent in industries to reduce the skin friction of polymer films. The weight of the oil impregnated in SiOP is approximately three times higher than that of silicone oil-infused PDMS (SiPDMS). Different from the SiPDMS surface on which oil dries easily, a slippery oil layer is stably formed on the SiOP surface. The fabricated SiOP surfaces have very low τ_ice values of approximately 1 kPa, which is much smaller than that of the SiPDMS surface. The SiOP with an oleamide content of 5 wt % exhibits the smallest τ_ice value of 0.88 kPa. The fabricated SiOP surfaces maintain their superior icephobicity for more than 30 icing/deicing cycles, demonstrating their enhanced lubrication lifetime. In addition, the ice freezing time of a water droplet of 7 μL in volume is significantly delayed on the SiOP surface compared with that on the SiPDMS surface. The present results demonstrate that the proposed SiOP surface can help provide superior icephobic performance with the aid of the incorporation of oleamide into the conventional SiPDMS. The developed icephobic SiOP can be utilized to satisfactorily resolve the lubricant drought problem of conventional icephobic surfaces by empolying oleamide as a complementary slip agent.

Frost Delay of a Water-Absorbing Surface with Engineered Wettability via Nonfreezing Water

Frost is common when a solid surface is subjected to a humid and cold environment. It can cause various inconveniences, complications, or fatal accidents. Water-repellent surfaces have demonstrated an antifreezing capability by enabling the water droplets to roll or bounce off before they freeze. However, these surfaces are often limited by their inability to shed the small water condensates, which can eventually grow and freeze. Recently, surfaces that can rapidly absorb and hydrogen bond with these water condensates have demonstrated significant delay in frost formation and growth. This is attributed to a lower freezing temperature of the absorbed water which makes it stay in a nonfreezing state. Herein, we report a surface with preferential wettability of water over oil (i.e., superhydrophilic and oleophobic wettability) that can significantly delay frost formation. The surface is fabricated by copolymerizing poly(ethylene glycol) diacrylate (PEGDA) and perfluorinated acrylate (1H,1H,2H,2H-heptadecafluorodecyl acrylate, HDF-acrylate) applied to a silane-grafted glass substrate (HDF-PEGDA). An HDF-PEGDA surface can quickly absorb condensed water which enables it to delay frost formation and growth for up to 20 min at a surface temperature of -35 °C. Also, the surface demonstrates that its frost-resistant capability remains almost unaffected even after being submerged in an oil bath due to its in-air oil repellency. Differential scanning calorimetry (DSC) measurements reveal that the significant quantity of absorbed water in an HDF-PEGDA surface remains in a nonfreezing state with a T_m value as low as -33 °C. A mathematical model that can predict the time at which the surface begins to be covered with frost is developed. Finally, an HDF-PEGDA is layered with a PEGDA copolymerized with sodium acrylate (Na-acrylate) that enables the continuous release of the absorbed water by posing forward osmotic pressure and regeneration of an HDF-PEGDA surface.

From Sticky to Slippery: Self-Functionalizing Lubricants for In Situ Fabrication of Liquid-Infused Surfaces

Liquid-infused surfaces offer a versatile approach to create self-cleaning coatings. In such coatings, a thin film of a fluid lubricant homogeneously coats the substrate and thus prevents direct contact with a second, contaminating liquid. For stable repellency, the interfacial energies need to be controlled to ensure that the lubricant is not replaced by the contaminating liquid. Here, we introduce the concept of self-functionalizing lubricants. Functional molecular species that chemically match the lubricant but possess selective anchor groups are dissolved in the lubricant and self-adhere to the surface, forming the required surface chemistry in situ from within the applied lubricant layer. To add flexibility to the self-functionalizing concept, the substrate is first primed with a thin polydopamine base layer, which can be deposited to nearly any substrate material from aqueous solutions and retains reactivity toward electron-donating groups such as amines. The temporal progression of the in situ functionalization is investigated by ellipsometry and quartz crystal microbalance and correlated to macroscopic changes in contact angle and contact angle hysteresis. The flexibility of the approach is underlined by creating repellent coatings with various substrate/lubricant combinations. The prepared liquid-infused surfaces significantly reduce cement adhesion and provide easy-to-clean systems under real-world conditions on shoe soles.

Intrusion of liquids into liquid-infused surfaces with nanoscale roughness

We present a theoretical study of the intrusion of an ambient liquid into the pores of a nanocorrugated wall w. The pores are prefilled with a liquid lubricant that adheres to the walls of the pores more strongly than the ambient liquid does. The two liquids are modeled as a binary liquid mixture of two species of particles, A and B. The mixture can decompose into a liquid rich in A particles, representing the ambient liquid, and another one rich in B particles, representing the liquid lubricant. The wall is taken to attract the B particles more strongly than the A particles. The ratio w-A/w-B of these interaction strengths is changed in order to tune the contact angle θ_{AB} formed by the A-rich/B-rich liquid interface between the two fluids and a planar wall, composed of the same material as the one forming the pores. We use classical density functional theory in order to capture the effects of microscopic details on the intrusion transition, which occurs as the concentration of the minority component or the pressure in the bulk of the ambient liquid is varied, moving away from bulk liquid-liquid coexistence within the single-phase domain of the A-rich bulk ambient liquid. These liquid structures have been studied as a function of the contact angle θ_{AB} and for various widths and depths of the pores. We also studied the reverse process in which a pore initially filled with the ambient liquid is refilled with the liquid lubricant. The location of the intrusion transition, with respect to its dependence on the contact angle θ_{AB} and the width of the pore, qualitatively follows the corresponding shift of the capillary-coexistence line away from the bulk liquid-liquid coexistence line, as predicted by a macroscopic capillarity model. Quantitatively, the transition found in the microscopic approach occurs somewhat closer to the bulk liquid-liquid coexistence line than predicted by the macroscopic capillarity model. The quantitative discrepancies become larger for narrower cavities. In cases in which the wall is completely wetted by the lubricant (θ_{AB}=0) and for small contact angles, the reverse transition follows the same path as for intrusion; there is no hysteresis. For larger contact angles, hysteresis is observed. The width of the hysteresis increases with increasing contact angle. A reverse transition is not found inside the domain within which the ambient liquid forms a single phase in the bulk once θ_{AB} exceeds a geometry-dependent threshold value. According to the macroscopic capillarity theory, for the considered geometry, this is the case for θ_{AB}>54.7^{∘}. Our computations show, however, that nanoscale effects shift this threshold value to much higher values. This shift increases strongly if the widths of the pores become smaller (below about ten times the diameter of the A and B particles).

Methods to stabilize aqueous supercooling identified by use of an isochoric nucleation detection (INDe) device

Stable aqueous supercooling has shown significant potential as a technique for human tissue preservation, food cold storage, conservation biology, and beyond, but its stochastic nature has made its translation outside the laboratory difficult. In this work, we present an isochoric nucleation detection (INDe) platform for automated, high-throughput characterization of aqueous supercooling at >1 mL volumes, which enables statistically-powerful determination of the temperatures and time periods for which supercooling in a given aqueous system will remain stable. We employ the INDe to investigate the effects of thermodynamic, surface, and chemical parameters on aqueous supercooling, and demonstrate that various simple system modifications can significantly enhance supercooling stability, including isochoric (constant-volume) confinement, hydrophobic container walls, and the addition of even mild concentrations of solute. Finally, in order to enable informed design of stable supercooled biopreservation protocols, we apply a statistical model to estimate stable supercooling durations as a function of temperature and solution chemistry, producing proof-of-concept supercooling stability maps for four common cryoprotective solutes.

Highly Transparent and Self-Healable Solar Thermal Anti-/Deicing Surfaces: When Ultrathin MXene Multilayers Marry a Solid Slippery Self-Cleaning Coating

Solar anti-/deicing can solve icing problems by converting sunlight into heat. One of the biggest problems, which has long been plaguing the design of solar anti-/deicing surfaces, is that photothermal materials are always lightproof and appear black, because of the mutual exclusiveness between generating heat and retaining transparency. Herein, a highly transparent and scalable solar anti-/deicing surface is reported, which enables the coated glass to exhibit high transparency (>77% transmittance at 550 nm) and meanwhile causes a >30 °C surface temperature increase relative to the ambient environment under 1.0 sun illumination. Such a transparent anti-/deicing surface can be fabricated onto a large class of substrates (e.g., glass, ceramics, metals, plastics), by applying a solid omniphobic slippery coating onto layer-by-layer-assembled ultrathin MXene multilayers. Hence, the surface possesses a self-cleaning ability to shed waterborne and oil-based liquids thanks to residue-free slipping motion. Passive anti-icing and active deicing capabilities are, respectively, obtained on the solar thermal surface, which effectively prevents water from freezing and simultaneously melts pre-formed ice and thick frost. The self-cleaning effect enables residue-free removal of unfrozen water and interfacially melted ice/frost to boost the anti-/deicing efficiency. Importantly, the surface is capable of self-healing under illumination to repair physical damage and chemical degradation.

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.

Recent Developments in Artificial Super-Wettable Surfaces Based on Bioinspired Polymeric Materials for Biomedical Applications

Inspired by nature, significant research efforts have been made to discover the diverse range of biomaterials for various biomedical applications such as drug development, disease diagnosis, biomedical testing, therapy, etc. Polymers as bioinspired materials with extreme wettable properties, such as superhydrophilic and superhydrophobic surfaces, have received considerable interest in the past due to their multiple applications in anti-fogging, anti-icing, self-cleaning, oil-water separation, biosensing, and effective transportation of water. Apart from the numerous technological applications for extreme wetting and self-cleaning products, recently, super-wettable surfaces based on polymeric materials have also emerged as excellent candidates in studying biological processes. In this review, we systematically illustrate the designing and processing of artificial, super-wettable surfaces by using different polymeric materials for a variety of biomedical applications including tissue engineering, drug/gene delivery, molecular recognition, and diagnosis. Special attention has been paid to applications concerning the identification, control, and analysis of exceedingly small molecular amounts and applications permitting high cell and biomaterial cell screening. Current outlook and future prospects are also provided.

Robust and durable liquid-repellent surfaces

This review provides a comprehensive summary of characterization, design, fabrication, and application of robust and durable liquid-repellent surfaces.

Non-wetting Liquid-Infused Slippery Paper

Liquid-infused slippery surfaces have replaced structural superhydrophobic surfaces in a plethora of emerging applications, hallmarked by their favorable self-healing and liquid-repelling characteristics. Their ease of fabrication on different types of materials and increasing demand in various industrial applications have triggered research interests targeted toward developing an environmental-friendly, flexible, and frugal substrate as the underlying structural and functional backbone. Although many expensive polymers such as polytetrafluoroethylene have so far been used for their fabrication, these are constrained by their compromised flexibility and non-ecofriendliness due to the use of fluorine. Here, we explore the development and deployment of a biodegradable, recyclable, flexible, and an economically viable material in the form of a paper matrix for fabricating liquid-infused slippery interfaces for prolonged usage. We show by controlled experiments that a simple silanization followed by an oil infusion protocol imparts an inherent slipperiness (low contact angle hysteresis and low tilting angle for sliding) to the droplet motion on the paper substrate and provides favorable anti-icing characteristics, albeit keeping the paper microstructures unaltered. This ensures concomitant hydrophobicity, water adhesion, and capillarity for low surface tension fluids, such as mustard oil, with an implicit role played by the paper pore size distribution toward retaining a stable layer of the infused oil. With demonstrated supreme anti-icing characteristics, these results open up new possibilities of realizing high-throughput paper-based substrates for a wide variety of applications ranging from biomedical unit operations to droplet-based digital microfluidics.

Dynamic Anti-Icing Surfaces (DAIS)

Remarkable progress has been made in surface icephobicity in the recent years. The mainstream standpoint of the reported antiicing surfaces yet only considers the ice-substrate interface and its adjacent regions being of static nature. In reality, the local structures and the overall properties of ice-substrate interfaces evolve with time, temperature and various external stimuli. Understanding the dynamic properties of the icing interface is crucial for shedding new light on the design of new anti-icing surfaces to meet challenges of harsh conditions including extremely low temperature and/or long working time. This article surveys the state-of-the-art anti-icing surfaces and dissects their dynamic changes of the chemical/physical states at icing interface. According to the focused critical ice-substrate contacting locations, namely the most important ice-substrate interface and the adjacent regions in the substrate and in the ice, the available anti-icing surfaces are for the first time re-assessed by taking the dynamic evolution into account. Subsequently, the recent works in the preparation of dynamic anti-icing surfaces (DAIS) that consider time-evolving properties, with their potentials in practical applications, and the challenges confronted are summarized and discussed, aiming for providing a thorough review of the promising concept of DAIS for guiding the future icephobic materials designs.

Fabrication Optimization of Ultra-Scalable Nanostructured Aluminum-Alloy Surfaces

Aluminum and its alloys are widely used in various industries. Aluminum plays an important role in heat transfer applications, where enhancing the overall system performance through surface nanostructuring is achieved. Combining optimized nanostructures with a conformal hydrophobic coating leads to superhydrophobicity, which enables coalescence induced droplet jumping, enhanced condensation heat transfer, and delayed frosting. Hence, the development of a rapid, energy-efficient, and highly scalable fabrication method for rendering aluminum superhydrophobic is crucial. Here, we employ a simple, ultrascalable fabrication method to create boehmite nanostructures on aluminum. We systematically explore the influence of fabrication conditions such as water immersion time and immersion temperature, on the created nanostructure morphology and resultant nanostructure length scale. We achieved optimized structures and fabrication procedures for best droplet jumping performance as measured by total manufacturing energy utilization, fabrication time, and total cost. The wettability of the nanostructures was studied using the modified Cassie-Baxter model. To better differentiate performance of the fabricated superhydrophobic surfaces, we quantify the role of the nanostructure morphology to corresponding condensation and antifrosting performance through study of droplet jumping behavior and frost propagation dynamics. The effect of aluminum substrate composition (alloy) on wettability, condensation and antifrosting performance was investigated, providing important directions for proper substrate selection. Our findings indicate that the presence of trace alloying elements play a previously unobserved and important role on wettability, condensation, and frosting behavior via the inclusion of defect sites on the surface that are difficult to remove and act as pinning locations to increase liquid-solid adhesion. Our work provides optimization strategies for the fabrication of ultrascalable aluminum and aluminum alloy superhydrophobic surfaces for a variety of applications.

Dual Component Passive Icephobic Coatings with Micron-Scale Phase-Separated 3D Structures

A passive icephobic coating (τ_ice < 20 kPa) is an enabling technology to many industries, including aerospace and energy and power generation, with recent efforts in materials research identifying strategies to achieve this low adhesion threshold. To better meet this need, we have combined low surface energy perfluoropolyether (PFPE) and hydrophilic poly(ethylene glycol) (PEG) species in a segmented polyurethane thermoplastic elastomer. Coating microstructure presents a segregated 3D morphology at the micron-scale (1-100 μm) with discrete PFPE and continuous PEG phases self-similar through the thickness. Spray application produces a solid, mechanically tough film free of additive fluids or sacrificial elements, demonstrating exceptional ice adhesion reduction up to 1000× lower versus aluminum (τ_ice < 1 kPa), as measured under environmentally realistic accretion and centrifugal test shedding conditions. Finally, the modular nature of the synthetic system allows PEG and PFPE to be exchanged for poly(tetramethylene oxide) to investigate performance drivers.

Expanding Biomaterial Surface Topographical Design Space through Natural Surface Reproduction

Surface topography is a tool to endow biomaterials with bioactive properties. However, the large number of possible designs makes it challenging to find the optimal surface structure to induce a specific cell response. The TopoChip platform is currently the largest collection of topographies with 2176 in silico designed microtopographies. Still, it is exploring only a small part of the design space due to design algorithm limitations and the surface engineering strategy. Inspired by the diversity of natural surfaces, it is assessed as to what extent the topographical design space and consequently the resulting cellular responses can be expanded using natural surfaces. To this end, 26 plant and insect surfaces are replicated in polystyrene and their surface properties are quantified using white light interferometry. Through machine-learning algorithms, it is demonstrated that natural surfaces extend the design space of the TopoChip, which coincides with distinct morphological and focal adhesion profiles in mesenchymal stem cells (MSCs) and Pseudomonas aeruginosa colonization. Furthermore, differentiation experiments reveal the strong potential of the holy lotus to improve osteogenesis in MSCs. In the future, the design algorithms will be trained with the results obtained by natural surface imprint experiments to explore the bioactive properties of novel surface topographies.

Brushable Lubricant-Infused Porous Coating with Enhanced Stability by One-Step Phase Separation

Slippery lubricant-infused porous surface (SLIPS) is a promising solution to undesired adhesion. Unfortunately, the complicated fabrication process and limited coating area block its practical applications. Herein, we report a one-step strategy to fabricate polypropylene-based SLIPS coatings through thermally induced phase separation, in which the lubricant is in situ infiltrated within a polymer network formed during cooling. The solid-liquid-phase separation process was monitored by an in situ hot-stage microscope. Such coating performs outstanding self-cleaning, anti-corrosion, and anti-bacterial performance, as well as enhanced stability of the lubricant layer because the lubricant is well adapted in the structure.

Preparation and Application of ZIF-8 Thin Layers

Herein we compare various preparation methods for thin ZIF-8 layers on a Cu substrate for application as a host material for omniphobic lubricant-infused surfaces. Such omniphobic surfaces can be used in thermal engineering applications, for example to achieve dropwise condensation or anti-fouling and anti-icing surface properties. For these applications, a thin, conformal, homogeneous, mechanically and chemically stable coating is essential. In this study, thin ZIF-8 layers were deposited on a Cu substrate by different routes, such as (i) electrochemical anodic deposition on a Zn-covered Cu substrate, (ii) doctor blade technique for preparation of a composite layer containing PVDF binder and ZIF-8, as well as (iii) doctor blade technique for preparation of a two-layer composite on the Cu substrate containing a PVDF-film and a ZIF-8 layer. The morphology and topography of the coatings were compared by using profilometry, XRD, SEM and TEM techniques. After infusion with a perfluorinated oil, the wettability of the surfaces was assessed by contact angle measurements, and advantages of each preparation method were discussed.

Lubrication dynamics of swollen silicones to limit long term fouling and microbial biofilms

Bacterial contamination and biofilm formation on medical devices remain a costly and serious healthcare problem. Silicone (polydimethylsiloxane, PDMS) elastomers are common biomaterials but are susceptible to bacterial surface contamination and biofilm growth. 'Self-lubricated' PDMS elastomers (iPDMS) have the potential to greatly reduce rates of cell attachment, biofilm formation and infection. Cross-linked PDMS elastomers immersed in PDMS oil swell to an equilibrium concentration to form a swollen network, and then form a surface liquid layer through syneresis. Herein we have measured the swelling and syneresis kinetics as a function of time, viscosity (1.5 to 10 cSt), and cross-linking density to optimize the surface lubricant layer formation, and resistance to biofouling. The lubricant layer thickness was measured in situ (optical profilometry and AFM) for flat and micro-textured surfaces, as a function of time and swelling ratio, to be in a range from 0.1 to 1 μm, and continuously increases with time. We show this continuous generation is likely due to a gradual, dynamic re-structuring of the elastomer network. Long term antifouling properties of (10 cSt) iPDMS were tested for Pseudomonas aeruginosa growth in a flow culture bioreactor, and after 30 d showed a 10³ to 10⁴ reduction of bacterial cell density for iPDMS compared to conventional PDMS elastomers. This long term performance and non-specific activity makes them highly suitable for biomedical devices, such as urinary catheters.

Predicting Hemiwicking Dynamics on Textured Substrates

The ability to predict liquid transport rates on textured surfaces is key to the design and optimization of devices and processes such as oil recovery, coatings, reaction-separation, high-throughput screening, and thermal management. In this work we develop a fully analytical model to predict the propagation coefficients for liquids hemiwicking through micropillar arrays. This is carried out by balancing the capillary driving force and a viscous resistive force and solving the Navier-Stokes equation for representative channels. The model is validated against a large data set of experimental hemiwicking coefficients harvested from the literature and measured in-house using high-speed imaging. The theoretical predictions show excellent agreement with the measured values and improved accuracy compared to previously proposed models. Furthermore, using lattice Boltzmann (LB) simulations, we demonstrate that the present model is applicable over a broad range of geometries. The scaling of velocity with texture geometry, implicit in our model, is compared against experimental data, where good agreement is observed for most practical systems. The analytical expression presented here offers a tool for developing design guidelines for surface chemistry and microstructure selection for liquid propagation on textured surfaces.

The challenge of lubricant-replenishment on lubricant-impregnated surfaces

Lubricant-impregnated surfaces are two-component surface coatings. One component, a fluid called the lubricant, is stabilized at a surface by the second component, the scaffold. The scaffold can either be a rough solid or a polymeric network. Drops immiscible with the lubricant, hardly pin on these surfaces. Lubricant-impregnated surfaces have been proposed as candidates for various applications, such as self-cleaning, anti-fouling, and anti-icing. The proposed applications rely on the presence of enough lubricant within the scaffold. Therefore, the quality and functionality of a surface coating are, to a large degree, given by the extent to which it prevents lubricant-depletion. This review summarizes the current findings on lubricant-depletion, lubricant-replenishment, and the resulting understanding of both processes. A multitude of different mechanisms can cause the depletion of lubricant. Lubricant can be taken along by single drops or be sheared off by liquid flowing across. Nano-interstices and scaffolds showing good chemical compatibility with the lubricant can greatly delay lubricant depletion. Often, depletion of lubricant cannot be avoided under dynamic conditions, which warrants lubricant-replenishment strategies. The strategies to replenish lubricant are presented and range from spraying or stimuli-responsive release to built-in reservoirs.

Bioinspired Tough Organohydrogel Dynamic Interfaces Enabled Subzero Temperature Antifrosting, Deicing, and Antiadhesion

Icing of water (moisture) at subzero temperatures with different length scales is harmful to a variety of applications spanning from large-scale aircraft to small camera lens. Existing strategies relying on controlling the surface structure and material are encumbered with shortcomings of short frost delay time, poor durability, and difficulty in large-scale production. Inspired from the mucus secretion of mollusks, we introduce organohydrogel dynamic interfaces that can perform dynamic and reversible exchange of the cryoprotectant and water at the interface, resulting in exceptional antifrosting, antiadhesion, and deicing properties with long-term durability. The replenishable coating shows superlubrication to the surface ice with a sliding angle up to 1.9 ± 0.4^o and a frost delay time up to 970 ± 31 min in the presence of water spray (99% relative humidity) at subzero temperatures. The strategy offers a reliable and scalable solution to prevent engineering surfaces, i.e., aircraft, pavement, bridge, and other public facilities, from icing/frosting and ice adhesion, even under extreme cold environments.

Modified Microwave Sensor with a Patterned Ground Heater for Detection and Prevention of Ice Accumulation

Ice accumulation on aircraft is known to negatively impact the aerodynamic and mechanical operation, sometimes resulting in catastrophic failure. Recently, microwave resonators have gained interest as durable and reliable frost and ice detectors. Here, a microwave resonator sensor with built-in heating capability patterned into the ground plane was designed, fabricated, and tested to investigate real-time ice and frost growth. Sensing was performed on surfaces with anti-icing coatings to quantitatively analyze the effectiveness of these materials. The sensor was also tested to determine its ability to evaluate different deicing methods. The sensor itself was a split-ring resonator (SRR) operating at 5.82 GHz, which could effectively distinguish between water and ice by detecting changes in the dielectric properties on or around its surface. This application was particularly suited for an SRR due to the extreme difference between the relative permittivity of water (ε = 90) and ice (ε = 3.2) at 5 GHz and 0 °C. The results from this sensor can be used to determine the holdover time of various coatings to resist ice formation. This study validates the use of SRRs as ice detection sensors for applications where ice and frost are of great interest, such as on aircraft, roads, or walkways.

Enhanced Condensation on Liquid-Infused Nanoporous Surfaces by Vibration-Assisted Droplet Sweeping

Condensation is a universal phenomenon that occurs in nature and industry. Previous studies have used superhydrophobicity and liquid infusion to enable superior liquid repellency due to reduced contact angle hysteresis. However, small condensate droplets remain immobile on condensing surfaces until they grow to the departing size at which the body force can overcome the contact line pinning force. Hence, condensation heat transfer is limited by these remaining droplets that act as thermal barriers. To break these limitations, we introduce vibrational actuation to a slippery liquid-infused nanoporous surface (SLIPS) and show enhanced droplet mobility, controllable condensate repellency, and more efficient heat transfer compared to static SLIPSs. We demonstrate 39% smaller departing droplet size and 8× faster droplet departing speeds on the dynamic vibrating SLIPS compared to the nonactuated SLIPS. To understand the implications of these behaviors on heat transfer, we investigate the condensate area coverage and droplet distribution to verify enhanced dewetting on dynamic vibrating SLIPSs. Using well-validated heat transfer models, we demonstrate enhanced condensation heat transfer on dynamic SLIPSs due to the higher population of smaller condensate droplets (<100 μm). In addition to condensation heat transfer, we also show that vibrating SLIPSs can enhance droplet collection. This work utilizes the synergistic combination of surface chemistry and mechanical actuation to realize enhanced droplet mobility and heat transfer in an electrically controllable and switchable manner.

Fabrication of Ultralow Ice-Adhesion Slippery Liquid Infused Porous Surfaces on Aluminum Alloy (7075-T651)

Slippery liquid infused porous surfaces (SLIPS) have been considered to be potential and effective method for anti-icing. Much work needed to be done for the application in field. In this study, SLIPS were successfully fabricated on 7075-T651 aluminum alloy by anodizing in phosphoric acid solution with three different voltage parameters and coating lubricant. Then the most suitable anodization parameters of samples were selected through the anti-icing performance tests. The best as-prepared surface exhibited ultralow ice-adhesion strength, which reduced from 261 to 6 kPa. Meanwhile, the freezing time of water-drop on aluminum alloy surfaces have been dramatically delayed at −5 and −10 °C (humidity of 75% ± 5%), respectively. Moreover, the durability of the SLIPS have also been investigated. Cycles of icing/deicing, mechanical damage, thermal and UV exposure were used to investigate the durability of SLIPS, and SLIPS could still show low ice-adhesion strength.

Characterization of Ice-Binding Proteins from Sea-Ice Microalgae

Several species of polar microalgae are able to live and thrive in the extreme environment found within sea ice, where ice crystals may reduce the organisms' living space and cause mechanical damage to the cells. Among the strategies adopted by these organisms to cope with the harsh conditions in their environment, ice-binding proteins (IBPs) seem to play a key role and possibly contribute to the success of microalgae in sea ice. Indeed, IBPs from microalgae predominantly belong to the so-called "DUF 3494-IBP" family, which today represents the most widespread IBP family. Since IBPs have the ability to control ice crystal growth, their mechanism of function is of interest for many potential applications. Here, we describe methods for a classical determination of the IBP activity (thermal hysteresis, recrystallization inhibition) and further methods for protein activity characterization (ice pitting assay, determination of the nucleating temperature).

Precursor-Film-Mediated Thermocapillary Motion of Low-Surface-Tension Microdroplets

In contrast to microdroplet condensation with high contact angles, the one with low contact angles remains unclear. In this study, we investigated dynamics of microdroplet condensation of low-surface-tension liquids on two flat substrate surfaces by using reflection interference confocal microscopy. Spontaneous migration toward relatively larger droplets was first observed for the microdroplets nucleated on the hydrophilic quartz surface. The moving microdroplets showed a contact angle hysteresis of ∼0.5°, which is much lower than the values observed on typical flat substrates and is within the range observed on slippery lubricant-infused porous surfaces. Because the microdroplets on the hydrophobic polydimethylsiloxane surface did not move, we concluded that the ultrathin precursor film is formed only on the hydrophilic surface, which reduces a resistive force to migration. Also, reduced size of droplets promotes the thermocapillary motion, which is induced by a gradient in local temperature inside a small microdroplet arising due to the difference in size of adjacent droplets.

Enabling phase transition of infused lubricant in porous structure for exceptional oil/water separation

The fundamental mechanism behind oil/water separation materials is their surface wettability that allows either oil or water to pass through. The conventional materials for oil/water separation generally have extreme wettability, namely superhydrophilic for water separation and superhydrophobic for oil separation. Using easily accessible materials that are medium hydrophobic or even relatively hydrophilic for preparing highly efficient oil/water separators have rarely been reported. In this work, a new strategy by triggering phase transition of infused lubricant from liquid to solid state in porous structure is realized in fabricating slippery lubricant infused porous structure for oil/water separations. By infusing polyester fabric with coconut oil, after phase transition, excellent water repellency and oil permeability by an absorbing-permeating mechanism are achieved, despite the low water contact angle on the new material. Although the new phase transformable slippery lubricant infused porous structure, features much milder hydrophobicity than conventional oil/water separators, it can remove diverse types of oil from water with high efficiencies. The phase transformable slippery lubricant infused porous structure is able to maintain their water repellency after immersing in high concentration salt (10 wt% NaCl), acid (25 % HCl), alkaline (25 % NH₃·H₂O) solutions for 120 h, showing remarkably functional durability in harsh environment. The lubricant phase transition mechanism proposed in this study is universally applicable to porous substrates with various chemical compositions and pore structures, such as porous sponges or even daily life breads, for creating efficient oil/water separators, which can serve as a novel accessible design principle of phase transformable slippery lubricant infused porous structure for eco-friendly oil/water separators.

Wetting-Controlled Localized Placement of Surface Functionalities within Nanopores

In the context of sensing and transport control, nanopores play an essential role. Designing multifunctional nanopores and placing multiple surface functionalities with nanoscale precision remains challenging. Interface effects together with a combination of different materials are used to obtain local multifunctionalization of nanoscale pores within a model pore system prepared by colloidal templating. Silica inverse colloidal monolayers are first functionalized with a gold layer to create a hybrid porous architecture with two distinct gold nanostructures on the top surface as well as at the pore bottom. Using orthogonal silane- and thiol-based chemistry together with a control of the wetting state allows individual addressing of the different locations within each pore resulting in nanoscale localized functional placement of three different functional units. Ring-opening metathesis polymerization is used for inner silica-pore wall functionalization. The hydrophobized pores create a Cassie-Baxter wetting state with aqueous solutions of thiols, which enables an exclusive functionalization of the outer gold structures. In a third step, an ethanolic solution able to wet the pores is used to self-assemble a thiol-containing initiator at the pore bottom. Subsequent controlled radical polymerization provides functionalization of the pore bottom. It is demonstrated that the combination of orthogonal surface chemistry and controlled wetting states can be used for the localized functionalization of porous materials.

Hard Quasicrystalline Coatings Deposited by HVOF Thermal Spray to Reduce Ice Accretion in Aero-Structures Components

Weather hazards, in particular icing conditions, are an important contributing factor in aviation accidents and incidents worldwide. Many different anti-icing strategies are currently being explored to find suitable long-lasting solutions, such as surface engineering, which can contribute to reduce ice accumulation. Quasicrystals (QCs) are metallic materials, but with similar properties to those of ceramic materials, such as low thermal and electrical conductivities, and high hardness. In particular, QCs that have low surface energy are commercially used as coatings to replace polytetrafluoroethylene (PTFE), also known as Teflon, on frying pans, as they do not scratch easily. PTFE exhibits excellent anti-wetting and anti-icing properties and therefore QCs appear as good candidates to be employed as ice-phobic coatings. Al-based QCs have been applied by High Velocity Oxyfuel (HVOF) thermal spray on typically used aeronautic materials, such as Ti and Al alloys, as well as steels. The coatings have been characterized and evaluated, including the measurement of hardness, roughness, wetting properties, ice accretion behavior in an icing wind tunnel (IWT), and ice adhesion by a double lap shear test. The coatings were studied, both as-deposited, as well as after grinding, in order to study the effect of the surface roughness and morphology on the ice accretion and adhesion properties. The QC coating was compared with PTFE and two polyurethane (PU)-based commercial paints, one of them known to have anti-icing properties, and the results indicate an ice accretion reduction relative to these two materials, and ice adhesion lower than bare AA6061-T6, or the PU paint in the ground version of one of the two QCs. Since the QC coatings are hard (GPa Vickers hardness > 5), a durable behavior is expected.

Reducing Static and Impact Ice Adhesion with a Self-Lubricating Icephobic Coating (SLIC)

Ice accumulation and adhesion can problematically occur on many engineering systems, such as electrical power networks, wind turbines, communication towers, and aircraft. An optional solution to these icing problems is the use of surfaces/coatings with low ice adhesion properties: Icephobic surfaces. Icephobic surfaces/coatings are very beneficial, as they facilitate the removal of ice or retard its formation and do not require the use of any sort of energy. A compact icing research tunnel (CIRT) was employed to measure ice tensile adhesion strength for both impact and static ice on a conventional metal surface (aluminum) and on a Self-Lubricating Icephobic Coating (SLIC) surface. The static ice consisted of deionized water slowly poured over the surface and left to be frozen on the test specimen surface at stationary conditions, while impact ice consisted of droplets of mean volumetric diameter (MVD) of 13 μm impacting the test specimen surface at a velocity of 40 m/s and freezing and accreting dynamically. The results revealed that static ice has an ice tensile adhesion stress higher than that of impact ice for the conditions used, consistent with previous studies. Additionally, a reduction of more than half was observed in ice tensile adhesion stress for SLIC compared to aluminum for both impact and static ice, and this performance stayed consistent even after multiple icing tests on the same sample. The SLIC coating hydrophobicity (roll-off angle and contact angle) also demonstrated resilience to icing and mechanical abrasion, confirming the self-healing properties.

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.

Inner Surface Design of Functional Microchannels for Microscale Flow Control

Fluidic flow behaviors in microfluidics are dominated by the interfaces created between the fluids and the inner surface walls of microchannels. Microchannel inner surface designs, including the surface chemical modification, and the construction of micro-/nanostructures, are good examples of manipulating those interfaces between liquids and surfaces through tuning the chemical and physical properties of the inner walls of the microchannel. Therefore, the microchannel inner surface design plays critical roles in regulating microflows to enhance the capabilities of microfluidic systems for various applications. Most recently, the rapid progresses in micro-/nanofabrication technologies and fundamental materials have also made it possible to integrate increasingly complex chemical and physical surface modification strategies with the preparation of microchannels in microfluidics. Besides, a wave of researches focusing on the ideas of using liquids as dynamic surface materials is identified, and the unique characteristics endowed with liquid-liquid interfaces have revealed that the interesting phenomena can extend the scope of interfacial interactions determining microflow behaviors. This review extensively discusses the microchannel inner surface designs for microflow control, especially evaluates them from the perspectives of the interfaces resulting from the inner surface designs. In addition, prospective opportunities for the development of surface designs of microchannels, and their applications are provided with the potential to attract scientific interest in areas related to the rapid development and applications of various microchannel systems.

The Inhibition of Icing and Frosting on Glass Surfaces by the Coating of Polyethylene Glycol and Polypeptide Mimicking Antifreeze Protein

The development of anti-icing, anti-frosting transparent plates is important for many reasons, such as poor visibility through the ice-covered windshields of vehicles. We have fabricated new glass surfaces coated with polypeptides which mimic a part of winter flounder antifreeze protein. We adopted glutaraldehyde and polyethylene glycol as linkers between these polypeptides and silane coupling agents applied to the glass surfaces. We have measured the contact angle, the temperature of water droplets on the cooling surfaces, and the frost weight. In addition, we have conducted surface roughness observation and surface elemental analysis. It was found that peaks in the height profile, obtained with the atomic force microscope for the polypeptide-coated surface with polyethylene glycol, were much higher than those for the surface without the polypeptide. This shows the adhesion of many polypeptide aggregates to the polyethylene glycol locally. The average supercooling temperature of the droplet for the polypeptide-coated surface with the polyethylene glycol was lower than for the polypeptide-coated surface with glutaraldehyde and the polyethylene-glycol-coated surface without the polypeptide. In addition, the average weight of frost cover on the specimen was lowest for the polypeptide-coated surface with the polyethylene glycol. These results argue for the effects of combined polyethylene glycol and polypeptide aggregates on the locations of ice nuclei and condensation droplets. Thus, this polypeptide-coating with the polyethylene glycol is a potential contender to improve the anti-icing and anti-frosting of glasses.

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.