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Slippery liquid-infused porous surface (SLIPS) based on Nepenthes pitcher plant has attracted increasing interest in many applications, particularly for mitigating icing hazard. Aside from exhibiting a water repellency, such surfaces have low contact angle hysteresis of <2.5° and low tilt angle of <5°. Nonetheless, SLIPS still suffer from challenges related to the oil depletion that reduces their service life. Herein, two different approaches, namely, microtexturing and the use of oil absorbent, are presented to effectively produce the slippery surfaces for the enhanced durability of engineered lubricant-infused materials. In the first approach, the replication method was employed to produce liquid-infused textured surfaces (LITS) through the chemical etching technique. Analysis such as lubricant depletion/recovery, confirmed that the presence of microtextures and lubricant viscosity can have significant roles in controlling the oil migration rate. Furthermore, merging microtexturing and slipperiness in LITS can enhance the icephobic performance. Such surface demonstrated an ice adhesion strength of less than 20 kPa, which is four orders of magnitude lower than the pristine surface. Furthermore, LITS can offer more long-lasting icephobic properties compared with pristine surface lacking microtextures. For the second strategy, the lubricant-loaded carriers were used to prohibit the rapid oil consumption, thus prolonging the life service of the prepared coatings. Accordingly, the negative pressure was applied to promote the incorporation of the lubricant within carrier pores and increase the carrier loading capacity. For this purpose, the thermogravimetric analysis (TGA), and the BET (Brunauer, Emmett and Teller) method have been used to evaluate the lubricant infusion quantitively. High oil content (around 50 wt. %) has been commonly used to enhance icephobic performance, but the presence of excessive amount of lubricant within the matrix can result in decreased mech

Mitigating icing hazards is of interest for many technological applications. One solution is to employ low ice adhesion coatings, either passively or in combination with active de-icing systems. Nevertheless, comparing different low ice adhesion surfaces can be challenging. Studies generally report the average shear stress, calculated as the ratio of applied force to the ice-substrate contact area; however, the fracture mechanism at the ice-substrate interface is rarely reported. There are two fracture mechanisms that can occur at the interface: stress-dominated and toughness-dominated. Average shear stress is only meaningful when performing adhesion tests in a stress-dominated regime; otherwise, interface stresses are underestimated and misleading. This study presents a new understanding of ice adhesion mechanisms combining experimental and numerical methods, demonstrating how the traditional ice adhesion reporting method can lead to errors up to 400%. Using a simple fracture model, the study shows that the stress-dominated fracture regime in the horizontal push test is favored by smaller ice diameter and greater ice thickness, and is also affected by the load force position. The identification of the two fracture regimes is required for the correct understanding and reproducibility of ice adhesion results, enabling better design and characterization of icephobic coatings and materials.

Electrical power systems, and more specifically electrical insulators are vulnerable to losing their functionality in severe meteorological conditions. Accumulation of ice or pollution can harm the electrical insulators. A layer of pollution can lead to accumulation of a conductive layer on top of the insulator. The contaminated high-voltage insulator in wet conditions could lead into a leakage current which flows through the surface of the insulator. This layer of conductive material on the insulator can lead to flashover which could result in the breakdown of the insulator. Therefore, anti-icing and self-cleaning coatings could be of great interest for electrical insulators. Superhydrophobic coatings have the potential to be used for anti-icing and self-cleaning properties. A lot of researchers have been focused on superhydrophobicity, yet most of the research carried out in this domain lack durability studies and the developed coatings have small life spans under harsh environmental conditions. Regenerative superhydrophobic coatings could solve this problem. These coatings will regain their superhydrophobicity after being ruptured or degraded. This research aims to fabricate silicone-based regenerative superhydrophobic coatings and study their durability and consequently their potential applications in electrical insulators. With that said, a superhydrophobic coating containing hydrophobic aerogel microparticles and polydimethylsiloxane modified silica nanoparticles within a PDMS based matrix containing Trifluoropropyl POSS (F-POSS) and Xiamater PMX-series silicone oil as superhydrophobicity regenerating agents were fabricated by spin-coating method. The fabricated coating showed a contact angle of 169.5° and a contact angle hysteresis of 6°. The self-cleaning ability of the developed coating was attested and studied by dry contamination test. The superhydrophobicity regeneration of the developed coating was also put at the test by plasma deterioration and variou

Smart icephobic coatings have attracted much attention owing to their promising application prospects in reducing ice adhesion, decreasing ice nucleation temperature, and delaying freezing time. Such coatings can sense changes in environmental stimuli, such as temperature, humidity, pressure, and pH, and provide an anti-icing or deicing response. These coatings can be categorized into several groups depending on the type of stimuli. In the present thesis, we chose two different smart icephobic strategies to develop novel coatings with enhanced anti-icing and deicing properties. First, aqueous self-lubricating coatings were developed by incorporating the polyethylene glycol (PEG)–polydimethylsiloxane (PDMS) copolymer in an elastomeric matrix. The presence of hydrophilic groups on PEG–PDMS copolymers can contribute to the formation of a quasi-liquid-like layer (QLL) that can improve the icephobic performance of the coatings. Surface analysis of the fabricated coatings confirmed that blending these copolymers into the elastomeric matrix increased the effective contact area between the water droplet and surface. Moreover, increased copolymer content reduced the ice nucleation temperature and prolonged the freezing-delay time. Two different methods, namely, push-off adhesion and centrifugal adhesion tests, were applied to study ice adhesion on the coatings. In general, adding PEG–PDMS copolymer into the PDMS matrix produced an unfrozen lubricating layer, resulting in decreased ice adhesion. Although excessive copolymer content saturated the coating with copolymer, which led to phase separation. Consequently, the surface roughness heightened; therefore, the ice adhesion strength increased owing to the mechanical interlocking between the ice and surface. Second, given the capability of phase change materials (PCMs) to restore and release a large amount of latent heat during the phase change process, we designed a smart icephobic coating by embedding PCM microcapsules into

Hypothesis: Characterizing the microstructure of an ice/surface interface and its effect on the icephobic behavior of surfaces remains a significant challenge. Introducing X-ray Computed Tomography (XCT) can provide unprecedented insights into the internal (porosity) and interfacial structures, i.e. wetting regime, between (super)hydrophobic surfaces and ice by visualizing these optically inaccessible regions. Experiments: Frozen droplets with controlled volume were deposited on top of metallic and polymeric substrates with different levels of wettability. Different modes of XCT (3D and 4D) were utilized to obtain information on the internal and interfacial structure of the ice/surface system. The results were supplemented by conventional surface analysis techniques, including optical profilometry and contact angle measurements. Findings: Using XCT on ice/surface systems, the 3D and 4D (imaging with temporal resolution) structural information can be visualized. From these datasets, qualitative and quantitative results were obtained, not only for characterizing the interface but also for analyzing the entire droplet/surface system, e.g., measurement of porosity size, shape, and location. These results highlight the potential of XCT in the characterization of both droplets and substrates and proves that the technique can aid to develop hydrophobic surfaces for use as icephobic materials.

Industries around the world use active methods, which include thermal, mechanical and chemical approaches, to reduce icing on aerodynamic surfaces such as wind turbines and aircraft. However, they are often inefficient, costly, and pollute the environment. For years, new coatings with anti-icing properties (so-called icephobic coatings) have been developed to either replace or work in tandem with active systems. In this study, coatings were designed based on an epoxy gelcoat commonly used for wind turbines through chemical modification with spherosilicate derivatives. Di- and tri-functional spherosilicates have both groups that increase the degree of hydro-/icephobicity of composites and groups capable of interacting with epoxy resin and amine hardener. The icephobicity of the surface was determined using ice adhesion. The lowest value of this parameter reached a value of 186 kPa, a 30 % reduction compared to the unmodified coating. In addition, the hydrophobicity of the surface was determined (the highest water contact angle was equal to 103°). A correlation was observed, proven in many works, that as the surface roughness increases, the anti-icing properties deteriorate. For individual modifications, it was also shown that hydrophobicity has a positive effect on ice adhesion. The work also examined the surface zeta potential and determined the durability of the properties after 100 icing/deicing cycles.

Ice accumulation on wind turbine blades due to the impact of supercooled water droplets can be reduced by the application of surfaces with anti-icing properties. Hydrophobic surfaces are considered as a promising solution because of their water repellent behavior. In recent years, short-pulsed laser technologies have been developed as an efficient technique to modify the surface properties of materials. However, the anti-icing properties of such surfaces have not yet been validated. In this work, a hybrid modification of polyester resin-based gelcoats was adopted. Laser patterning (LP) was used to produce periodic surface structures on modified unsaturated polyester resin (UPR) substrates. One of the innovations of this research is the utilization of novel purpose-made chemical modifiers for gelcoats. The implementation of linear polymethylhydrosiloxane (PMHS) as a building block is a key improvement in terms of durability and functionality of the coating, since there is an option of introducing not only groups bonding in the polyester into one molecule, but also groups that increase hydrophobicity. The other novelty is a successfully conducted experiment combining such chemical modification with laser texturization of the surface. The influence of the laser energy, pattern shape, and spatial periods on the topographical characteristics and hydrophobicity as well as the anti-icing properties of the produced surfaces were investigated. To characterize the surface topography of the produced structures, scanning electron microscopy (SEM) and profilometer were utilized. Measurements of the wettability parameters (static contact angle and contact angle hysteresis) on the treated surfaces allowed the identification of the influence of wetting behavior and laser parameters on the investigated materials. Anti-icing properties were characterized by ice adhesion (IA) and freezing delay time (FDT) tests. It was found that hybrid modification of unsaturated polyester resin by c

In this paper, hydrophobic nanocomposite coatings based on polyurethane (PUR) modified by nano-silica and silane-based compounds were manufactured by spraying. The main challenge was to assess and improve the hydrophobic as well as anti-icing properties of initially hydrophilic polymer coatings. The prepared nanocomposite coatings were characterized by means of scanning electron microscopy (SEM), optical profilometry and X-ray photoelectron spectroscopy (XPS). The results obtained showed that in order to achieve hydrophobicity, appropriate amounts of nano-silica must be incorporated in the coating, and complete coverage by nano-silica particles is necessary for achieving hydrophobicity. Coating adhesion and the durability of the hydrophobic behaviour were also studied by scratch test and frosting/defrosting cycles, respectively. The results show that use of both nano-silica and silane-based compounds improve the hydrophobic and anti-icing properties of the coating as compared to a non-modified PUR topcoat. A synergistic e ect of both additives was observed. It was also found that the anti-icing behaviour does not necessarily correlate with surface roughness and the materials’ wetting properties.

Wettability is one of the fundamental characterizations of each solid surface which might affect the final surface properties in different manners. In the light of various Mother Nature’s masterpieces, specifically Lotus leaves, as a symbol of purity, the nature-inspired superhydrophobic surfaces have received immense attention. In the present thesis, two different approaches are opted to effectively create artificial self-cleaning/superhydrophobic surfaces to enhance the water-repellency of the engineered silicone rubber and Teflon materials. Firstly, the atmospheric-pressure plasma treatment was used to produce self-cleaning/superhydrophobic high-temperature vulcanized silicone rubber (HTV-SR) surfaces via etching technique. This approach is significant since the use of an atmospheric-pressure plasma system as a simple, fast and environmentally friendly technique is combined with compressed air as an eco-friendly plasma gas which offers great potential for the mass production of superhydrophobic surfaces in an industrial scale. Using plasma treatment, a substantial enhancement in the water-repellency of HTV-SR surfaces, i.e., static water contact angle (WCA) >160° and a contact angle hysteresis (CAH) <3°, was attained due to the formation of coral-like micro-nanostructures on the surface. Possessing the appropriate surface structures depends highly on the composition of plasma jet affected by plasma operating parameters. Thus, the role of significant plasma operating parameters on the surface water-repellency was assessed with the help of a design of experiment (DoE) method to determine the near-optimal operating parameters. The icephobic properties are divided into two categories of anti-icing and de-icing properties. Anti-icing properties correspond to the delay in the ice formation, while de-icing properties illustrate the reduction of the adhesion strength of the ice formed on the surface. The well-known ice adhesion measurement techniques, i.e., the centrifug

Given the role of micro-nanostructures in producing superhydrophobic and icephobic surfaces and the importance of high-quality replication of these micro-nanostructures in direct replication processes, we evaluated the effect of processing parameters on the superhydrophobicity, icephobicity, and replication quality of silicone rubber surfaces created via micro-compression molding. Molding pressure, mold temperature, curing time, and part thickness were selected as the processing parameters to be assessed. We used a response surface methodology to illustrate the optimal values of the selected processing parameters. Molding pressure and part thickness were the main influencing parameters to attain the superhydrophobicity. In a second set of experiments, we assessed the replication quality of silicone rubber surfaces of variable thickness subjected to different molding pressures. Each part thickness had an optimal molding pressure for obtaining the best replication quality. Surfaces having the highest replication quality also demonstrated the longest freezing delay and confirmed their potential use as anti-icing surfaces. Although all developed superhydrophobic surfaces showed icephobicity, the influence of processing parameters affecting ice adhesion was complex.

Herein, polymer processing systems are used to fabricate superhydrophobic high-temperature vulcanized (HTV) silicone rubber surfaces by direct replication. HTV silicone rubber is one of the main polymeric housing materials used in high-voltage insulators. The selected polymer processing techniques are compression molding and injection molding.The direct replication approach requires that a template or insert having the desired surface patterns be replicated onto a target polymer surface via a polymer processing. The appropriate micro-nanostructures, required for achieving ultra-water-repellency, were created on the insert materials (an aluminum alloy) using a wet-chemical etching method. As a flawless demolding is essential to acquire desirable replication quality, an antistiction coating was applied to the insert surfaces prior to the molding process to ensure the thorough removal of the silicone rubber during the demolding. The resulting silicone rubber surfaces possessed micro-nanostructures producing a water contact angle (WCA) of >160° and a contact angle hysteresis (CAH) of <3°. The surface roughness of the aluminum inserts was optimized at HCl concentrations of 15 wt.%. The self-cleaning properties of the produced ultra-water-repellent silicone rubber surfaces were rigorously investigated to ensure a self-cleaning surface at real outdoor imitated conditions. The presence of air pockets in between the surface asperities produced the Cassie-Baxter regime. The consistency of these air pockets is crucial for attaining the self-cleaning properties. A series of tests, including droplet impact, water-jet impact, trapped air layer, and severe droplet contact tests were conducted to confirm the stability of the Cassie-Baxter regime. A comprehensive series of self-cleaning experiments involving both suspended and non-suspended contaminants, e.g., kaolin, carbon black, and silica as well as contaminant-applying methods, e.g., dropwise, spraying, wet or dry contamination

The processes of phase transformation continue to affect our natural and industrial worlds in a range of scales from large-scale lava flows in nature to micro-and nano- scale applications in industry. Enhancement of the knowledge framework of these processes and understanding the accompanying physical phenomena are keys to resolve challenges in scientific research and obtain rational engineering evaluations for a wide range of industrial application such as 3D printing, rapid prototyping, thermal spray coating, power plants, aerospace and turbine industries. A great deal of work has been done in the past few decades on these matters, and significant progress has been made; however, much of it remains unraveled. The main difficulty stems from the intertwined effect of heat transfer, fluid dynamics, and phase change physics with the combination of complex wetting behaviors of the contact-line. In this thesis, we focus on solidification and condensation near the contact-line. For solidification near the contact-line, we have studied the onset of solidification and its relevant physical parameters and explored ways to delay the start of solidification inspired by the unique ice-resisting abilities of penguin feathers and certain plant leaves. The dynamics of solidification and spreading is also studied and new hypothesis is introduced to explain the contact-line pinning due to solidification. Finally, in condensation near the contact-line, we have introduced a novel biphilic surface with large scale cost-effective manufacturing process and analyzed and compared its heat transfer efficiency and water droplet mobility to traditional hydrophobic and hydrophilic structures.

The processes of phase transformation continue to affect our natural and industrial worlds in a range of scales from large-scale lava flows in nature to micro-and nano- scale applications in industry. Enhancement of the knowledge framework of these processes and understanding the accompanying physical phenomena are keys to resolve challenges in scientific research and obtain rational engineering evaluations for a wide range of industrial application such as 3D printing, rapid prototyping, thermal spray coating, power plants, aerospace and turbine industries. A great deal of work has been done in the past few decades on these matters, and significant progress has been made; however, much of it remains unraveled. The main difficulty stems from the intertwined effect of heat transfer, fluid dynamics, and phase change physics with the combination of complex wetting behaviors of the contact-line. In this thesis, we focus on solidification and condensation near the contact-line. For solidification near the contact-line, we have studied the onset of solidification and its relevant physical parameters and explored ways to delay the start of solidification inspired by the unique ice-resisting abilities of penguin feathers and certain plant leaves. The dynamics of solidification and spreading is also studied and new hypothesis is introduced to explain the contact-line pinning due to solidification. Finally, in condensation near the contact-line, we have introduced a novel biphilic surface with large scale cost-effective manufacturing process and analyzed and compared its heat transfer efficiency and water droplet mobility to traditional hydrophobic and hydrophilic structures.

Spontaneous removal of liquid, solidifying liquid and solid forms of matter from surfaces, is of significant importance in nature and technology, where it finds applications ranging from self-cleaning to icephobicity and to condensation systems. However, it is a great challenge to understand fundamentally the complex interaction of rapidly solidifying, typically supercooled, droplets with surfaces, and to harvest benefit from it for the design of intrinsically icephobic materials. Here we report and explain an ice removal mechanism that manifests itself simultaneously with freezing, driving gradual self-dislodging of droplets cooled via evaporation and sublimation (low environmental pressure) or convection (atmospheric pressure) from substrates. The key to successful self-dislodging is that the freezing at the droplet free surface and the droplet contact area with the substrate do not occur simultaneously: The frozen phase boundary moves inward from the droplet free surface toward the droplet-substrate interface, which remains liquid throughout most of the process and freezes last. We observe experimentally, and validate theoretically, that the inward motion of the phase boundary near the substrate drives a gradual reduction in droplet-substrate contact. Concurrently, the droplet lifts from the substrate due to its incompressibility, density differences, and the asymmetric freezing dynamics with inward solidification causing not fully frozen mass to be displaced toward the unsolidified droplet-substrate interface. Depending on surface topography and wetting conditions, we find that this can lead to full dislodging of the ice droplet from a variety of engineered substrates, rendering the latter ice-free.

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.

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.

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.

A superhydrophobic and icephobic surface were investigated on aluminum alloy substrate. Anodizing was used first to create a micro-nanostructured aluminum oxide underlayer on the alloy substrate. In a second step, the rough surface was coated with RF-sputtered polytetrafluoroethylene (PTFE or Teflon®). Scanning electron microscopy images showed a “bird's nest”-like structure on the anodized surface. The RF-sputtered PTFE coating exhibited a high static contact angle of ~165° with a very low contact angle hysteresis of ~3°. X-ray photoelectron spectroscopy (XPS) results showed high quantities of CF3 and CF2 groups, which are responsible for the hydrophobic behavior of the coatings. The performance of this superhydrophobic film was studied under atmospheric icing conditions. These results showed that on superhydrophobic surfaces ice-adhesion strength was 3.5 times lower than on the polished aluminum substrate.