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Three superhydrophobic surfaces have been prepared on an aluminium substrate, which was roughened by acid etching to form a nano-/micro-topological surface structure, and then the surface was modified by coating with a PTES (a fluorinated coupling agent), TTPS (a siloxane coupling agent) or PA (an aliphatic coupling agent) layer. Their surface wettability in terms of water contact angle (CA), sliding angle (SA) and water droplet impact dynamics was studied under different humidities at −10 °C. The reduction of ice adhesion was also investigated under both ambient and condensate environments. The results indicated that the icephobic properties of these three superhydrophobic surfaces in the sub-zero environment varied wildly. The PTES surface can maintain excellent sliding and rebounding ability of a water droplet even under extremely condensate conditions (−10 °C and relative humidity (RH) 90%), while others cannot. It is worth noting that the ice adhesion obviously increased under the condensate environment, but no apparent ice-anchoring effect was observed on any of the three superhydrophobic surfaces. In addition, a water condensing dynamic study at sub-zero temperature revealed a distinctive Leidenfrost phenomenon-like jumping behavior of condensed droplets on all three superhydrophobic surfaces with the highest jumping scale and frequency on the PTES surface. The excellent icephobic property of the PTES surface indicates that the choice of a suitable chemical modification for superhydrophobic surfaces has a significant influence on preserving water-repellency and icephobicity under extremely condensing conditions.

Icing of surfaces is commonplace in nature and technology, affecting everyday life and sometimes causing catastrophic events. Understanding (and counteracting) surface icing brings with it significant scientific challenges that requires interdisciplinary knowledge from diverse scientific fields such as nucleation thermodynamics and heat transfer, fluid dynamics, surface chemistry, and surface nanoengineering. Here we discuss key aspects and findings related to the physics of ice formation on surfaces and show how such knowledge could be employed to rationally develop surfaces with extreme resistance to icing (extraordinary icephobicity). Although superhydrophobic surfaces with micro-, nano-, or (often biomimetic) hierarchical roughnesses have shown in laboratory settings (under certain conditions) excellent repellency and low adhesion to water down to temperatures near or below the freezing point, extreme icephobicity necessitates additional important functionalities. Other approaches, such as lubricant-impregnated surfaces, exhibit both advantages and serious limitations with respect to icing. In all, a clear path toward passive surfaces with extreme resistance to ice formation remains a challenge, but it is one well worth undertaking. Equally important to potential applications is scalable surface manufacturing and the ability of icephobic surfaces to perform reliably and sustainably outside the laboratory under adverse conditions. Surfaces should possess mechanical and chemical stability, and they should be thermally resilient. Such issues and related research directions are also addressed in this article.

Experimental results aimed at understanding the different mechanisms of ice accretion on surfaces with different wettabilities are presented. Ice accretion was studied on a hydrophilic and a superhydrophobic surface of NACA 0021 airfoils, during tests inside an icing wind tunnel. Visualization of ice accretion was performed using an infrared camera, which allows an enhanced view of liquid water and ice present on the airfoil surface compared to the optical imaging. The use of the infrared camera permitted identification of different ice shapes and ice formation mechanisms on the test articles: on the hydrophilic sample, a compact ice front accreted, whereas on the superhydrophobic sample, small isolated ice islands formed. In addition, the ice on the superhydrophobic sample was more susceptible to be shed from the surface, as shown by shedding of several ice islands due to aerodynamic drag during tests. Combined analysis of infrared camera images and optical images confirmed that the fraction of the airfoil covered by ice decreases for the superhydrophobic sample, for a two minute test, for all the input heat power tested.

A new method has been developed to study the role of hydrogen bonding in ice adhesion and to minimize the effect of this mechanism on ice adhesion. Metals were coated with a mono-molecular layer that had either strong hydrophobic properties or strong hydrophilic properties. Self-assembling monolayers (SAMs) of varying degrees of hydrophobicity/hydrophilicity were created by mixing the hydrophobic and hydrophilic components. The SAM structure and quality were examined using atomic force microscopy, and the degree of the SAM hydrophobicity/hydrophilicity was characterized by the contact angle of water on the monolayer surfaces. Then, water was frozen on the top of the SAM and the shear strength of the interface between ice and SAM was measured. A good correlation between the contact angle of water and the ice adhesion strength was shown and the fraction of ice adhesion caused by hydrogen bonding was determined. It is revealed that hydrogen bonding significantly enhances ice adhesion. PACS No.: 61

In this paper, an anti-icing coating with an aqueous lubricating layer is reported. This anti-icing coating can be directly applied to various substrates, and the ice adhesion strength on the coated surfaces can be lowered greatly as compared to uncoated substrates. We demonstrate for the first time that the formed ice on this anti-icing coating can be blown off by a wind action in the wind tunnel with a controlled temperature and wind velocity. Moreover, the low ice adhesion of the anti-icing coating can be maintained even when the temperature is lowered to -53 oC. The robustness and durability of the anti-icing coating are proved by the icing/de-icing experiments. The results show that the anti-icing coating with an aqueous lubricating layer is of great promise for practical applications.

Icing of surfaces is commonplace in nature, technology and everyday life, bringing with it sometimes catastrophic consequences. A rational methodology for designing materials with extraordinary resistance to ice formation and adhesion remains however elusive. We show that ultrafine roughnesses can be fabricated, so that the ice nucleation-promoting effect of nanopits on surfaces is effectively counteracted in the presence of an interfacial quasiliquid layer. The ensuing interface confinement strongly suppresses the stable formation of ice nuclei. We explain why such nanostructuring leads to the same extremely low, robust nucleation temperature of ∼−24 °C for over three orders of magnitude change in RMS size (∼0.1 to ∼100 nm). Overlaying such roughnesses on pillar-microtextures harvests the additional benefits of liquid repellency and low ice adhesion. When tested at a temperature of −21 °C, such surfaces delayed the freezing of a sessile supercooled water droplet at the same temperature by a remarkable 25 hours.

Undesired ice accumulation leads to severe economic issues and, in some cases, loss of lives. Although research on anti-icing has been carried out for decades, environmentally harmless, economical, and efficient strategies for anti-icing remain to be developed. Recent researches have provided new insights into the icing phenomenon and shed light on some promising bio-inspired anti-icing strategies. The present review critically categorizes and discusses recent developments. Effectively trapping air in surface textures of superhydrophobic surfaces weakens the interaction of the surfaces with liquid water, which enables timely removal of impacting and condensed water droplets before freezing occurs. When ice already forms, ice adhesion can be significantly reduced if liquid is trapped in surface textures as a lubricating layer. As such, ice could be shed off by an action of wind or its gravity. In addition, bio-inspired anti-icing strategies via trapping or introducing other media, such as phase change materials and antifreeze proteins, are discussed.

The state-of-the-art of icing protection systems for helicopter rotor blades is based on active thermal de-icing systems that require large amounts of power. This work focused on assessing the potential icephobicity of superhydrophobic coatings as an alternative passive strategy. Ice shedding tests were conducted in a helicopter blade icing chamber, to simulate atmospheric icing conditions. Ice accretion and shedding were tested on four different materials, including two common metals and two superhydrophobic materials, with the objective of evaluating icephobic potential for anti-icing purposes. Coating test results showed a strong influence of temperature and surface roughness on the ice adhesion: the strength increased when temperature decreased and roughness increased. Ice regime was independent of the type of surface used, but superhydrophobic surfaces resulted in a thinner ice shape in comparison with common metals, which resulted in a shorter shedding time, especially in rime ice conditions. The relationship between ice regime and adhesion load showed that ice adhesion load substantially increases in rime ice conditions, demonstrating that ice regime is an important parameter in the ice adhesion process. Additional results showed that superhydrophobic surfaces were associated with a decrease in the adhesion load with respect to the baseline materials ranging from the 16% to the 70% in the best case; but this reduction may not be revealing for practical applications as ice reduction mechanisms need to be first understood.

There is a growing interest and debate on the role of surface coatings to combat ice accretion on solid surfaces. Most of the studies have focused on "icephobicity", with the aim of either reducing ice adhesion strength or delaying freezing time. Here we present an alternative strategy, which relies on the superhydrophobicity of surfaces as a way to enhance liquid water shedding from a surface prior to water freezing. To show in which conditions liquid water drops can rebound and be shed from a solid surface before freezing, drop impact experiments were performed on solid targets characterized by different wettability and thermal properties. The main result is that, when frost formation is avoided on the surfaces (i.e. if surface temperature is above dew point), drop dynamics, including spreading and recoiling, remains unaffected by solidification effects. In particular, drop rebound can still be achieved down to-20°C.

L'accumulation de glace sur les surfaces exposees conduit a des difficultes operationnelles et des efforts? de maintenance eleves pour les lignes de transport d'electricite, les antennes, les avions, les bateaux et les vehicules de transport terrestre. Dans ce travail, le depot de Hexamethyldisiloxane polymerise par plasma a basse pression (HMDSO-PP) a ete realise pour creer des revetements avec des proprietes superhydrophobes/glaciophobes sur la surface de l'aluminium. Avant de realiser le revetement a faible energie de surface, les surfaces d'aluminium ont ete anodisees ou immergees dans de l'eau bouillante pour produire des surfaces micro/nano structurees. Les parametres du plasma ont ete optimises pour trouver les conditions optimales afin d'obtenir un angle de contact eleve et une faible hysteresis de l'angle de contact. Pour ce faire, la methode Taguchi-Grey, a ete utilisee comme l'une des techniques de conception experimentale (DOE). La stabilite des revetements a egalement ete etudiee dans des conditions de vieillissement accelere tels que la degradation par UV, l'immersion dans de l'eau distillee, et les solutions avec differents pH, et l'effet de plusieurs cycles de glacage/de- glacage. Les resultats obtenus ont montres que les revetements PP-HMDSO ont de bonnes stabilites apres l'exposition aux rayons UV et apres l'immersion dans de l'eau distillee. Toutefois, la propriete de glaciophobe du revetement PP-HMDSO depose sur l'aluminium anodise a ete diminuee apres quinze cycles de glacage/de- glacage. L'etude de l'effet du temps de depot de PP-HMDSO ont montre que l'augmentation du temps de depot conduit a une diminution de la force d'adherence de la glace sur un revetement de PP-HMDSO depose sur l'aluminium anodise alors qu'il n'a pas d'effet significatif sur le revetement PP-HMDSO depose sur la surface d'aluminium traitee dans l'eau bouillant. Ainsi, le revetement PP-HMDSO superhydrophobe a egalement fourni une protection contre la corrosion au substrat d'aluminium. - Accumulated ice on exposed surfaces leads to operational difficulties and extensive maintenance for power transmission lines, antennas, aircraft, ships, and ground transportation vehicles. In the present study, the low pressure plasma polymerized Hexamethyldisiloxane (PP-HMDSO) film is deposited on aluminum surfaces to create a superhydrophobic coating with icephobic properties. Prior to the deposition of this low surface energy coating, aluminum surfaces were anodized or immersed in boiling water to make micro/nano structured surfaces. Plasma parameters were optimized in order to find the best optimum conditions for having high static contact angle and low contact angle hysteresis. Hence, the Grey-based Taguchi method was used as one of the Design of Experiment (DOE) techniques. The stability of coatings was studied under accelerated aging conditions such as UV degradation, immersion in distilled water and different pH solutions, and several icing/deicing cycles. It was observed that the PP-HMDSO coatings are quite stable against UV exposure and immersion in distilled water. However, the icephobicity of the PP-HMDSO coating deposited on the anodized aluminum decreased after fifteen icing/de-icing cycles. The stability of the developed coating was improved against several icing/de-icing cycles by increasing the deposition time of plasma polymerized coating from 15 to 25 minutes. The results showed that increasing the deposition time of plasma polymerization leads to decrease of the ice adhesion strength of coatings on anodized aluminum while it has no significant effect on the PP-HMDSO coating deposited on a water-treated aluminum surface. Finally, the superhydrophobic PP-HMDSO coating also provides anti-corrosion protection for the aluminum substrate.

In this work, we measured the adhesion strength of artificially created glaze ice (similar to accreted in nature) on rough fluoropolymer-based hydrophobic surfaces with different contact angle (CA) and wetting hysteresis. The previously reported direct correlation between ice repellency and CA on superhydrophobic surfaces is shown to be only valid for surfaces with low wetting hysteresis. Another correlation was found between wetting hysteresis and ice adhesion strength on rough surfaces with similar chemistry.

The study on water-repellent coatings and their effect on adhesion of ice is summarized as follows: 1 A new type of water-repellent coating consisting of perfluorinated PTFE particles dispersed in PVdF resin binder exhibited a contact angle of about 150 degrees. This extraordinarily high contact angle is attributed to the surface roughness and surface heterogenvity of the new materials taking into account the presence of air between water and new material in the high PTFE content resin. 2 The free surface energy of the water-repellent coatings has a linear relationship with the adhesion of ice. 3 The greater the surface roughness of high wettability materials, the better the adhesion. And the larger the surface roughness of water-repellent coatings, the poorer the adhesion. This difference is based apparently on the water-penetrating properties attributed to the difference in anchor effect on rough surface.

The term “icephobicity” has emerged in the literature recently. An extensive discussion took place on whether the icephobicity is related to the superhydrophobicity and the consensus is that there is no direct correlation. Besides the parallel between the icephobicity and superhydrophobicity for water/ice repellency, there are similarities on other levels including the hydrophobic effect/hydrophobic interactions, mechanisms of protein folding and ice crystal formation. In this paper, we report how ice adhesion is different from water using force balance analysis and why superhydrophobic surfaces are not necessary icephobic. We also present experimental data on anti-icing of various surfaces and suggest a definition of icephobicity, which is broad enough to cover a variety of situations relevant to de-icing including low adhesion strength and delayed ice crystallization and bouncing.

The adsorption of water on solid surfaces is a scientific evergreen which again recently prompted considerable attention in the materials, nano-, and surface science communities, respectively, due to conflicting evidence presented in the most highly regarded scientific journals. This mini review is a brief and personal perspective of the current literature (and our own data) about water adsorption for two examples, namely graphene and silicatene, which are both two-dimensional (2D) crystals. Silicatene, an inorganic companion of graphene, is intriguing as it presents us with the possibility to synthesize a 2D analog to zeolites by doping this crystalline silicon film. The wettability by water and whether or not support effects of epitaxial 2D crystals are present is of concern. Regarding applications: some 2D crystals appear promising for the hydrogen evolution reaction, i.e., hydrogen generation from water; a functionalization of graphene (by oxygen/water) to graphene oxide may be interesting for metal-free catalysis; the latest highlight in this field appears to be “icephobicity”, an application related to the hydrophobicity of surfaces.

Tribology involves the study of friction, wear, lubrication, and adhesion, including biomimetic superhydrophobic and icephobic surfaces. The three aspects of icephobicity are the low ice adhesion, repulsion of incoming water droplets prior to freezing, and delayed frost formation. Although superhydrophobic surfaces are not always icephobic, the theoretical mechanisms behind icephobicity are similar to the entropically driven hydrophobic interactions. The growth of ice crystals in saturated vapor is partially governed by entropically driven diffusion of water molecules to definite locations similarly to hydrophobic interactions. The ice crystal formation can be compared to protein folding controlled by hydrophobic forces. Surface topography and surface energy can affect both the icephobicity and hydrophobicity. By controlling these properties, micro/nanostructured icephobic concrete was developed. The concrete showed ice adhesion strength one order of magnitude lower than regular concrete and could repel incoming water droplets at −5 °C. The icephobic performance of the concrete can be optimized by controlling the sand and polyvinyl alcohol fiber content.

We discuss mechanical forces that act upon a water droplet and a piece of ice on a rough solid surface and the difference between dewetting and ice fracture. The force needed to detach a water droplet depends on contact angle (CA) hysteresis and can be reduced significantly in the case of a superhydrophobic surface. The force needed to detach a piece of ice depends on the receding CA and the initial size of interfacial cracks. Therefore, even surfaces with very high receding CA may have strong adhesion to ice if the size of the cracks is small.

Ice on surfaces can have dramatic consequences for human activities. Over the last decades, the design of new materials with anti-icing properties has generated significant research efforts for the prevention of ice accretion. Here we investigate water freezing temperatures on untreated and negatively charged hydrophobic stainless steel surfaces and use these temperatures to evaluate icephobicity. Supercooled water microdroplets are deposited and undergo a slow controlled cooling until spontaneous freezing occurs. Textured hydrophobic stainless steel surfaces functionalized with anionic polyelectrolytes brushes display unexpectedly lower freezing temperatures, at least 7 °C lower than polished untreated steel. On the basis of the entropy reduction of the crystalline phase near a charged solid surface, we used a modification of the classical heterogeneous nucleation theory to explain the observed freezing temperatures lessening. Our results could help the design of new composite materials that more efficiently prevent ice formation.

Understanding ice formation from supercooled water on surfaces is a problem of fundamental importance and general utility. Superhydrophobic surfaces promise to have remarkable 'icephobicity' and low ice adhesion. Here we show that their icephobicity can be rendered ineffective by simple changes in environmental conditions. Through experiments, nucleation theory and heat transfer physics, we establish that humidity and/or the flow of a surrounding gas can fundamentally switch the ice crystallization mechanism, drastically affecting surface icephobicity. Evaporative cooling of the supercooled liquid can engender ice crystallization by homogeneous nucleation at the droplet-free surface as opposed to the expected heterogeneous nucleation at the substrate. The related interplay between droplet roll-off and rapid crystallization is also studied. Overall, we bring a novel perspective to icing and icephobicity, unveiling the strong influence of environmental conditions in addition to the accepted effects of the surface conditions and hydrophobicity.

using materials such as fl uorocarbons, organic materials, and inorganic materials, [ 6 ] which demonstrate signifi cant hydrophobic properties. Whereas the robust superhydrophobicity of these materials exists at around room temperature, the overwhelming majority of them will fail when put into a subzero degree environment. [ 7 ] It is well known that hydrophobicity and icephobicity properties are extremely important to favor cold environment devices, [ 8 ] such as aerofoils, power towers, ships, radars, and even pipes of airconditioners or refrigerators. Once ice forms on this equipment, they may fail to work normally or may even be damaged. Anti-icing surfaces have been studied since the 1950s. [ 9 ] However, it is still a great challenge to design and fabricate more effi cient ice repellent surfaces, which has aroused the interest of many researchers. [ 7 , 10–25 ]

We present a simple method to produce carbon nanotube-based films with exceptional superhydrophobicity and impact icephobicity by depositing acetone-treated single-walled carbon nanotubes on glass substrates. This method is scalable and can be adopted for any substrate, both flexible and rigid. These films have indicated a high contact angle, in the vicinity of 170°, proved both by static and dynamic analysis processes. The dynamic evaporation studies indicated that a droplet deposited on the treated films evaporated in the constant contact angle mode for more than 80% of the total evaporation time, which is definitely a characteristic of superhydrophobic surfaces. Furthermore, the acetone-functionalized films showed a strong ability to mitigate ice accretion from supercooled water droplets (-8 °C), when the droplets were found to bounce off the films tilted at 30°. The untreated nanotube films did not indicate similar behavior, and the supercooled water droplets remained attached to the films' surfaces. Such studies could be the foundation of highly versatile technologies for both water and ice mitigation.

Ice formation can have catastrophic consequences for human activity on the ground and in the air. Here we investigate water freezing delays on untreated and coated surfaces ranging from hydrophilic to superhydrophobic and use these delays to evaluate icephobicity. Supercooled water microdroplets are inkjet-deposited and coalesce until spontaneous freezing of the accumulated mass occurs. Surfaces with nanometer-scale roughness and higher wettability display unexpectedly long freezing delays, at least 1 order of magnitude longer than typical superhydrophobic surfaces with larger hierarchical roughness and low wettability. Directly related to the main focus on heterogeneous nucleation and freezing delay of supercooled water droplets, the observed ensuing crystallization process consisted of two distinct phases: one very rapid recalescent partial solidification phase and a subsequent slower phase. Observations of the droplet collision process employed for the continuous liquid mass accumulation up to the point of ice formation reveal a previously unseen atmospheric-pressure, subfreezing-temperature regime for liquid-on-liquid bounce. On the basis of the entropy reduction of water near a solid surface, we formulate a modification to the classical heterogeneous nucleation theory, which predicts the observed freezing delay trends. Our results bring to question recent emphasis on super water-repellent surface formulations for ice formation retardation and suggest that anti-icing design must optimize the competing influences of both wettability and roughness., Langmuir, 27 (6), ISSN:0743-7463, ISSN:1520-5827

Ice formation and accretion may hinder the operation of many systems critical to national infrastructure, including airplanes, power lines, windmills, ships, and telecommunications equipment. Yet despite the pervasiveness of the icing problem, the fundamentals of ice adhesion have received relatively little attention in the scientific literature and it is not widely understood which attributes must be tuned to systematically design "icephobic" surfaces that are resistant to icing. Here we probe the relationships between advancing/receding water contact angles and the strength of ice adhesion to bare steel and twenty-one different test coatings (∼200-300 nm thick) applied to the nominally smooth steel discs. Contact angles are measured using a commercially available goniometer, whereas the average strengths of ice adhesion are evaluated with a custom-built laboratory-scale adhesion apparatus. The coatings investigated comprise commercially available polymers and fluorinated polyhedral oligomeric silsesquioxane (fluorodecyl POSS), a low-surface-energy additive known to enhance liquid repellency. Ice adhesion strength correlates strongly with the practical work of adhesion required to remove a liquid water drop from each test surface (i.e., with the quantity [1 + cos θ(rec)]), and the average strength of ice adhesion was reduced by as much as a factor of 4.2 when bare steel discs were coated with fluorodecyl POSS-containing materials. We argue that any further appreciable reduction in ice adhesion strength will require textured surfaces, as no known materials exhibit receding water contact angles on smooth/flat surfaces that are significantly above those reported here (i.e., the values of [1 + cos θ(rec)] reported here have essentially reached a minimum for known materials).

In order to study in-flight ice adhesion at the droplet-scale, a strategy is presented to simulate the impact and solidification of a super cooled water droplet on a cooled substrate. Upon impact, nucleation is assumed to occur instantaneously, and properties of the droplet are chosen to account for the nucleation process. Simulations are performed in ANSYS Fluent using a coupled Volume of Fluid and Level-Set method to capture the air-water interface and an Enthalpy-Porosity method to capture the liquid-solid interface. Calibration of a simulation parameter, Amush, is performed in order to match experimental data for different surface types and surface temperatures. The calibrated simulation strategy is applied to low-speed, in-flight icing conditions. The effects of surface variation and droplet diameter variation are investigated, providing insight into the icephobicity of super hydrophobic surfaces. Numerical results suggest that large droplets (approximately 200 micron-diameter) will freeze and adhere to a super hydrophobic surface.

We use nanoparticle-polymer composites to demonstrate the anti-icing capability of superhydrophobic surfaces and report direct experimental evidence that such surfaces are able to prevent ice formation upon impact of supercooled water both in laboratory conditions and in natural environments. We find that the anti-icing capability of these composites depends not only on their superhydrophobicity but also on the size of the particles exposed on the surface. The critical particle sizes that determine the superhydrophobicity and the anti-icing property are in two different length scales. The effect of particle size on ice formation is explained by using a classical heterogeneous nucleation theory. This result implies that the anti-icing property of a surface is not directly correlated with the superhydrophobicity, and thus, it is uncertain whether a superhydrophobic surface is anti-icing without detailed knowledge of the surface morphology. The result also opens up possibilities for rational design of anti-icing superhydrophobic surfaces by tuning surface textures in multiple length scales.

A new treatment offers a simple and inexpensive method to reduce considerably ice adhesion on a wind turbine blade surface ensuring a safe and reliable energy production during winter periods. This treatment has icephobic characteristics, satisfactory mechanical, optical and electrical properties and doesn't alter the surface appearance. The technique consists in depositing a poly(tetrafluoroethylene) or PTFE coating, which strongly clings on a high porosity blade surface. A uniform coating was obtained by dipping the blade samples in a PTFE solution dispersion followed by annealing at 290°C for 2 min in an argon atmosphere. The resulting film yielded a contact angle around 145°, a hysteresis of 30°, a surface tension estimated to 11.7 mN/m and a slipping angle of 45° even at temperature as low as −6°C. The shear strength of ice adhesion was reduced by 80% compared to pristine blade surface at temperatures ranging from −1.8°C to −12.5°C. There was no observed effect of ice shedding events and no accelerated aging was observed through UVC irradiation and corrosive acidic solution on the hydrophobicity of the coated surface. The low surface energy of that coating is promising for its use in the wind turbine industry.

The Spinning Rotor Blade (SRB) is an apparatus developed at Anti-icing Material International Laboratory in collaboration with Bell Helicopter Textron to study ice physics, low energy de-icing systems and hydro- or ice-phobic coatings use for small helicopters. The SRB is a 1/18 subscale model of a small helicopter with 0.78 m diameter rotor of two blades rotated by a 10 hp engine to a tip speed of 130 m/s. The blades are 6066-T6 extruded aluminum with a NACA0012 airfoil of 69.64 mm chord and 0.315 m long. The icing tests were conducted in AMIL’s low speed closed loop Icing Wind Tunnel with a liquid water content of 0.84 g/m³, a median volumetric diameter of 26.7 ± 2.6 µm, an air speed of 15 ± 0.5 m/s and temperature of -15 ± 0.5°C. The power to rotate the SRB was 1 200 ± 120 W with a vibration of 2 ± 0.4 g; when the icing began, the power increased to 5 200 ± 1 400 W at a rate of 30 ± 4 W/s, suddenly, after 160 ±50 s, the power decreased, indicating that a piece of ice of 70 ± 15 mm length and about 4 g of weight was shed at the blade tip. The SRB is able to perform reproducible ice shedding tests with similar behavior to helicopters at low cost with repeatability below 30% and sensibility of ±5% for temperatures ranging from -5 to -20oC. The ice adhesive shear stress estimated from the SRB II at -15°C was 0.21 ± 0.06 MPa for aluminum. It decreased linearly when the temperature increased. Also, the adhesive shear stress obtained for icephobic Coating A was 0.10 MPa which is 2.1 less adhesive than aluminum, but its icephobicity is insufficient to be safely used on helicopters. Some empirical correlations for ice thickness, freezing fraction and adhesive shear stress were found with the SRB-II and also a criterion was proposed criterion to quantify the icephobicity of coating efficiency for helicopters, but without fundamental parametric scaling equations to helicopter, they are not helpful for helicopter.

International audience; Water drops oil hydrophobic microtextured materials sit on a mixture of solid and air. In standard superhydrophobic situations, the drop contacts more air than solid, so that we can think of exploiting the insulating properties of this sublayer. We show here that its presence induces a significant delay in freezing, when depositing water on cold solids. If the substrate is slightly tilted, these drops can thus be removed without freezing and without accumulating on the substrate, a property of obvious practical interest.

Understanding the complementary roles of surface energy and roughness on natural nonwetting surfaces has led to the development of a number of biomimetic superhydrophobic surfaces, which exhibit apparent contact angles with water greater than 150 degrees and low contact angle hysteresis. However, superoleophobic surfaces—those that display contact angles greater than 150 degrees with organic liquids having appreciably lower surface tensions than that of water—are extremely rare. Calculations suggest that creating such a surface would require a surface energy lower than that of any known material. We show how a third factor, re-entrant surface curvature, in conjunction with chemical composition and roughened texture, can be used to design surfaces that display extreme resistance to wetting from a number of liquids with low surface tension, including alkanes such as decane and octane.

Bio-inspired superhydrophobicity is a promising anti-icing (or deicing) strategy, but a superhydrophobic surface may lose its anti-icing capability once the deposited water freezes. Herein, it is shown that ice can be readily and repeatedly removed from the surface of superhydrophobic polyurethane sponges via a simple mechanical squeezing process. The sponges are fabricated through a mussel-inspired process and subsequent deposition of Ag nanoparticles. The resulting sponges are able to shed off the ice layers formed on their surfaces up to 90 times, exhibiting robust icephobic properties among the reported superhydrophobic surfaces. The mechanism for the excellent icephobicity is investigated by a highly sensitive microelectrobalance and a fluorescent labeling method. It is revealed that the icephobicity is attributed to low ice adhesion of the superhydrophobic sponges, as well as mechanical durability of their surface textures. The present findings provide a facile strategy to fabricate robust icephobic surfaces for various technological applications.

A superhydrophobic surface was obtained on a low-density polyethylene (LDPE) substrate using a facile method. The water contact angle and the sliding angle of the superhydrophobic LDPE surface were 155 ± 2° and 4°, respectively. The ice shear stress of the superhydrophobic LDPE surface was 2.08 times smaller than that of the flat LDPE surface. The superhydrophobic surface still showed excellent icephobicity and superhydrophobicity after undergoing a circulatory icing/deicing procedure five times. In addition, water condensation and its effect on the icephobicity of the as-prepared superhydrophobic surface were also studied.

Superhydrophobic surfaces are of fundamental and commercial interest as water does not wet the surface, leading to unique properties such as low slip angle, high contact angle, and icephobicity. These behaviours are achieved through a combination of low surface energy materials and high surface roughness. Two printing techniques were used to fabricate hydrophobic polymers into superhydrophobic surfaces. In one approach, a commercially available multi-jet modelling rapid prototyping machine was used to fabricate 3D superhydrophobic objects including helical conduits and porous membranes, using the standard printer resins. A robotic dispensing tool was also developed that enables greater freedom of material selection and feature shape. Both approaches were used to fabricate arrays of high aspect ratio surface features on which water assumes a nearly spherical shape and easily rolls off the surface at low tilt angles. The fabrication and wetting properties of surfaces made using these two techniques will be discussed.

Understanding the mechanism of ice adhesion on surfaces is crucial for anti-icing surfaces, and it is not clear if superhydrophobic surfaces could reduce ice adhesion. Here, we investigate ice adhesion on model surfaces with different wettabilities. The results show that the superhydrophobic surface cannot reduce the ice adhesion, and the ice adhesion strength on the superhydrophilic surface and the superhydrophobic one is almost the same. This can be rationalized by the mechanical interlocking between the ice and the surface texture. Moreover, we find that the ice adhesion strength increases linearly with the area fraction of air in contact with liquid.

The surface wettability control of solid materials has been considered as an essential aspect of surface chemistry. In the past decade, superhydrophobic surfaces have revealed a cornucopia of novel structural and functional properties, exhibiting considerable importance in both fundamental research and practical applications. In this review, we summarize the recent developments of superhydrophobic surfaces with unique structural and functional properties. Both the fabricative methods and the working performance of superhydrophobic surfaces with multidisciplinary functionalities including self-cleaning, icephobicity, anti-corrosion, drag reduction, transparency, anti-reflection, structural color, droplet transportation, anisotropy, oil–water separation, water supporting force, superamphiphobicity and responsive switching, have been discussed briefly. Finally, the current challenges and future prospects of this dynamic field are discussed based on our own opinion.

We study frost formation and its impact on icephobic properties of superhydrophobic surfaces. Using an environmental scanning electron microscope, we show that frost nucleation occurs indiscriminately on superhydrophobic textures without any particular spatial preference. Ice adhesion measurements on superhydrophobic surfaces susceptible to frost formation show increased adhesion over smooth surfaces with a strong linear trend with the total surface area. These studies indicate that frost formation significantly compromises the icephobic properties of superhydrophobic surfaces and poses serious limitations to the use of superhydrophobic surfaces as icephobic surface treatments for both on-ground and in-flight applications.