Prevention of ice accretion and adhesion on surfaces is relevant to many applications, leading to improved operation safety, increased energy efficiency, and cost reduction. Development of passive nonicing coatings is highly desirable, since current antiicing strategies are energy and cost intensive. Superhydrophobicity has been proposed as a lead passive nonicing strategy, yet the exact mechanism of delayed icing on these surfaces is not clearly understood. In this work, we present an in-depth analysis of ice formation dynamics upon water droplet impact on surfaces with different wettabilities. We experimentally demonstrate that ice nucleation under low-humidity conditions can be delayed through control of surface chemistry and texture. Combining infrared (IR) thermometry and high-speed photography, we observe that the reduction of water-surface contact area on superhydrophobic surfaces plays a dual role in delaying nucleation: first by reducing heat transfer and second by reducing the probability of heterogeneous nucleation at the water-substrate interface. This work also includes an analysis (based on classical nucleation theory) to estimate various homogeneous and heterogeneous nucleation rates in icing situations. The key finding is that ice nucleation delay on superhydrophobic surfaces is more prominent at moderate degrees of supercooling, while closer to the homogeneous nucleation temperature, bulk and air-water interface nucleation effects become equally important. The study presented here offers a comprehensive perspective on the efficacy of textured surfaces for nonicing applications.

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.

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.

With the recent progress in nanotechnology and material engineering, nano-based coatings have become multifunctional, smarter, efficient, versatile and durable. Superhydrophobic coatings are an important class of the smart coating family, which has gained recognition in coating science over the last few years. The uniqueness of superhydrophobic coatings arises from the various phenomenal innovations, and its development is expected to continue in the next decades. The bioinspired superhydrophobic surfaces are commonly obtained by designing a double-scale structure by using nanotechnology, followed by the addition of water repellent compounds. It lacks an overview article describing on the recent progress in superhydrophobic coatings and surfaces. In this perspective article, various fundamental aspects of wettability and related phenomena are discussed. We present and compare the existing methods for the preparation of superhydrophobic coatings. Properties of superhydrophobic coatings such as self-cleaning, anti-icing, anti-fouling, and anti-bacterial features were also introduced. The review also discusses various superhydrophobic technological breakthroughs and future trends in the preparation and application of these materials.

Biomimetic superhydrophobic surfaces show great potential in oil-water separation, anti-icing and self-cleaning. However, due to the instability caused by its fragile structure and non-durable superhydrophobicity, it is difficult to apply them in the actual field. Here, by introducing surface wettability and analysing the mechanism of superhydrophobic failure, it is concluded that the reason for the failure of the superhydrophobic surface comes from the transition of the surface energy and the hysteresis of the contact angle (CA). On the basis of this analysis, it is concluded that the principle of designing a durable superhydrophobic surface is to satisfy one of the following three points: improving the binding force between molecules, introducing durable materials and improving chemical durability. On this basis, a variety of preparation methods are proposed, such as assembly method and spray/dip coating method, and the design and preparation of a self-healing surface inspired by nature will also be included in the introduction. Last but not least, the preparation and application of a durable super-hydrophobic surface in oil-water separation, anti-icing and self-cleaning are also introduced in detail. This review reveals the conclusions and prospects of durable superhydrophobic surfaces, and aims to inspire more researchers to invest in this research.

Nature has created an array of superhydrophobic surfaces that possess water-repellent, self-cleaning and anti-icing properties. These surfaces have a number of potential applications in the biomedical industry, as they have the potential to control protein adsorption and cell adhesion. Natural superhydrophobic surfaces are typically composed of materials with a low intrinsic surface free-energy (e.g the cuticular waxes of lotus leaves and insect wings) with a hierarchical structural configuration. This hierarchical surface topography acts to decrease the contact area of water droplets in contact with the surface, thereby increasing the extent of the air/water interface, resulting in water contact angles greater than 150º. In order to employ these surfaces in biotechnological applications, fabrication techniques must be developed so that these multi-scale surface roughness characteristics can be reproduced. Additionally, these fabrication techniques must also be able to be applied to the material required for the intended application. An overview of some of the superhydrophobic surfaces that exist in nature is presented, together with an explanation of the theories of their wettability. Also included is a description of some of the biomedical applications of superhydrophobic surfaces and fabrication techniques that can be used to mimic superhydrophobic surfaces found in nature.

An aggressive impact of the formed ice on the surface of man-made objects can ultimately lead to serious consequences in their work. When icing occurs, the quality and characteristics of equipment, instruments, and building structures deteriorate, which affects the durability of their use. Delays in the adoption of measures against icing endanger the safety of air travel and road traffic. Various methods have been developed to combat de-icing, such as mechanical de-icing, the use of salts, the application of a hydrophobic coating to the surfaces, ultrasonic treatment and electric heating. In this review, we summarize the recent advances in the field of anti-icing and analyze the role of various additives and their operating mechanisms.

Water freezing remains a perennial topic of great relevance to many important aspects of our lives; from the climate to human society and from economics to medicine, frozen water profoundly influences our living environment and life activities. There have been numerous publications on water freezing; however, confusion regarding the process of freezing remains. In this review, we mainly focused on the nucleation aspects of water freezing; in particular, we focused on the effect of the surface morphology and nanostructure of foreign bodies. This review covers the recent progress in ice nucleation and anti-freezing strategies within the framework of nucleation principles. In this regard, we first summarize the crystal nucleation theories. Due to high interfacial energy, ice crystallization is primarily controlled by heterogeneous nucleation events, because the homogeneous nucleation barrier of ice is extremely high. In addition to the interfacial energy, the interfacial morphology or nanostructure of foreign bodies plays a diverse role under different supercooling regimes due to the Gibbs-Thomson effect. This effect gives rise to the inverse homogeneous-like nucleation phenomenon, in which foreign bodies have little influence on the nucleation barrier. This ensures the accurate measurement of the nucleation barrier, critical size, and water-ice interfacial energy, in agreement with the latest studies based on a microemulsions approach, metadynamics, the mW model, etc. As a consequence, anti-freezing strategies can be implemented by reducing the nucleation rate through restriction of the contact area of the water/substrate interface, by increasing the heterogeneous nucleation barrier through modification of the interfacial properties of foreign particles, including the interfacial structure and the interaction between the water and foreign particles and by kink kinetics. Within this context, the anti-freezing mechanism of superhydrophobic substrates was reviewed. Therefore, it follows that by significantly reducing the contact area between the water and substrate, superhydrophobic materials can effectively reduce the heterogeneous nucleation rate. We hope that this review will provide a unified picture and guidance for future work on water freezing.

This review examines how the concepts and ideas of crystallization can be extended further and applied to the field of mesoscopic soft materials. It concerns the structural characteristics vs. the macroscopic performance, and the formation mechanism of crystal networks. Although this subject can be discussed in a broad sense across the area of mesoscopic soft materials, our main focus is on supramolecular materials, spider and silkworm silks, and biominerals. First, the occurrence of a hierarchical structure, i.e. crystal network and domain network structures, will facilitate the formation kinetics of mesoscopic phases and boost up the macroscopic performance of materials in some cases (i.e. spider silk fibres). Second, the structure and performance of materials can be correlated in some way by the four factors: topology, correlation length, symmetry/ordering, and strength of association of crystal networks. Moreover, four different kinetic paths of crystal network formation are identified, namely, one-step process of assembly, two-step process of assembly, mixed mode of assembly and foreign molecule mediated assembly. Based on the basic mechanisms of crystal nucleation and growth, the formation of crystal networks, such as crystallographic mismatch (or noncrystallographic) branching (tip branching and fibre side branching) and fibre/polymeric side merging, are reviewed. This facilitates the rational design and construction of crystal networks in supramolecular materials. In this context, the (re-)construction of a hierarchical crystal network structure can be implemented by thermal, precipitate, chemical, and sonication stimuli. As another important class of soft materials, the unusual mechanical performance of spider and silkworm silk fibres are reviewed in comparison with the regenerated silk protein derivatives. It follows that the considerably larger breaking stress and unusual breaking strain of spider silk fibres vs. silkworm silk fibres can be interpreted according to the synergistically correlated hierarchical structures of the domain and crystal networks, which can be quantified by the hierarchical structural correlation and the four structural parameters. Based on the concept of crystal networks, the new understanding acquired will transfer the research and engineering of mesoscopic materials, particularly, soft functional materials, to a new phase.

Despite the relevance to most aspects of crystallization, a comprehensive understanding of the kinetics of heterogeneous nucleation has not been well established yet. In this paper, a new kinetic model based on the “steady-state” approach will be put forward to describe both heterogeneous and homogeneous nucleation. As a key point in this model, the effect of foreign particles on both the nucleation barrier, the “chain reaction” process and the transport of structural units is taken into account. Ranging from low to high supersaturations, heterogeneous nucleation plays a more comprehensive role in nucleation than we expected, depending on the size of foreign particles and the interaction and structural matching between foreign particles and the nucleating phase. It follows that genuine homogeneous nucleation may only be possible at very high supersaturations, and can become easier when convection is eliminated. The results have been verified by the CaCO3 nucleation experiments. This general model allows us to describe many unexpected nucleation phenomena for the first time, and will have significant impact on the control of nucleation, understanding of crystallization in microgravity, the measurement of the crystal–fluid interfacial tension, and crystallization in general.

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.

Recently the development of superhydrophobic surfaces with one-tier or hierarchical textures has drawn increasing attention because enhanced condensation heat transfer has been observed on such biomimetic surfaces in well-tailored supersaturation or subcooling conditions. However, the physical mechanisms underlying condensation enhancement are still less understood. Here we report an energy-based analysis on the formation and growth of condensate droplets on two-tier superhydrophobic surfaces, which are fabricated by decorating carbon nanotubes (CNTs) onto microscale fluorinated pillars. Thus-formed hierarchical surfaces with two tier micro/nanoscale roughness are proved to be superior to smooth surfaces in the spatial control of condensate droplets. In particular, we focus on the self-pulling process of condensates in the partially wetting morphology (PW) from surface cavities due to intrinsic Laplace pressure gradient. In this analysis, the self-pulling process of condensate tails is resisted by adhesion energy, viscous dissipation, contact line dissipation and line tension in a combined manner. This process can be facilitated by adjusting the configuration and length scale of the first-tier texture. The optimum design can not only lower the total resistant energy but also favor the out-of-plane motion of condensate droplets anchored in the first-tier cavity. It is also shown that engineered surface with hierarchical roughness is beneficial to remarkably mitigating contact line dissipation from the perspective of molecular kinetic theory (MKT). Our study suggests that scaling down surface roughness to submicron scale can facilitate the self-propelled removal of condensate droplets.This journal is © The Royal Society of Chemistry.

Aluminum (Al) is widely used in all forms of industry, including automobile, aerospace, transmission lines, and exchangers, and in general household appliances. Ice accumulation on Al surfaces may cause serious problems, especially during the winter, leading to critical damage to mechanical systems. In this study, we developed a superhydrophobic coating with anti-icing properties on an Al surface using a simple and cost-effective technique. The superhydrophobic dual-shape micro-/nanostructured (MN-) Al surface was fabricated by a facile chemical etching and an anodization method, followed by surface modification with polydimethylsiloxane (PDMS) via a simple thermal vapor deposition method. The static contact angle of the fabricated surface was more than 160 °C. Compared with the bare surface and the silicone oil-infused PDMS coating (SLIPS) on the MN-structured Al substrate, the fabricated superhydrophobic surface displayed excellent anti-icing. Ice formation on the superhydrophobic surface was delayed by 80 and 45 min at -5 °C and -10 °C, respectively, at a relative humidity of 80% ± 5%. The superhydrophobic surface demonstrated an increase of almost four and two times delay in icing time on the surface over bare and SLIPS surfaces, respectively. The coalescence induced jumping behavior of condensate water droplets was also investigated on the fabricated surfaces. The result indicates that the superhydrophobic surface can effectively delay ice/frost formation by the synergetic effect of surface morphology and the extremely low adhesive property of the surfaces, which allows the self-propelled jumping phenomenon at low temperature and high humidity. This proposed simple, fast, and cost-effective method could be applied to design large-scale anti-icing surfaces.

Ice accumulation on wind turbine blades reduces power generation efficiency and increases wind turbines’ maintenance cost, even causing equipment damage and casualties. In this work, in order to achieve passive anti-icing, a series of nano-pillar array structures with different diameters of from 100 to 400 nm and heights of from 400 to 1500 nm were constructed on the substrate bisphenol-A epoxy resin, which is generally used in the manufacturing of wind turbine blades. The as-constructed functional surface showed excellent water repellence, with a contact angle of up to 154.3°. The water repellence on the nano-pillar array structures could induce ultra-low ice adhesion as low as 7.0 kPa, finding their place in the widely recognized scope of icephobic materials. The underlying solid–ice interface mechanism was well revealed in regard to two aspects: the interface non-wetting regime and the stress concentration behavior on the nano-pillar array structured surface. A detailed discussion on both the factors presented here will help surface structure design and function of icephobic materials, especially for epoxy-based composite materials.

The elastic membranes with different surface stiffness were fabricated via spin-coating followed by the laser ablation. The as-fabricated elastic membrane exhibited superhydrophobicity with a rough microstructure. The droplet impacting experiment on the cold elastic superhydrophobic membrane was conducted, and the influence of surface stiffness and impacting speed on the droplet impacting process were investigated. It was found that the elastic superhydrophobic membrane exhibits a robust anti-icing performance compared with the elastic hydrophobic membrane. A lower surface stiffness corresponds to a larger deformation degree of the elastic membrane and to a smaller maximum droplet spreading diameter. Moreover, the contact time decreases with the increase of impacting speed as for the same stiffness of the cold elastic superhydrophobic membrane. The underlying mechanism of the cold elastic membrane with low ice adhesion may be due to the face that the deformation of the superhydrophobic membrane provides an elastic force for the droplet to detach from the surface and thus reduce the heat transfer between the droplet and the surface.

The current status of the use of nanoparticles for photothermal treatments is reviewed in detail. The different families of heating nanoparticles are described paying special attention to the physical mechanisms at the root of the light-to-heat conversion processes. The heating efficiencies and spectral working ranges are listed and compared. The most important results obtained in both in vivo and in vitro nanoparticle assisted photothermal treatments are summarized. The advantages and disadvantages of the different heating nanoparticles are discussed.

Facing various problems caused by icing in daily life, preparing photothermal deicing materials with wide applicability in high efficiency and low cost is not only a current research hotspot but also a great challenge. Herein, an economical spray-coating method is applied to prepare high-efficiency flexible photothermal icephobic copper mesh using micro silicon carbide (SiC) particles as photothermal conversion material and nano silica (SiO) particles as a surface superhydrophobic modifier. Owing to the excellent hierarchical micro-nanostructures, the SiC/SiO coated copper mesh exhibits a water contact angle (CA) of 162 ± 2° and a sliding angle (SA) of 3 ± 2°. Interestingly, the coated copper mesh exhibits exceptional mechanical durability against water droplet and water flow impact, repeated bending-twisting and tape-peeling. Benefitting from the robust superhydrophobicity, the SiC/SiO coating on the copper mesh can significantly delay the freezing time of the droplets and reduce the ice adhesion strength. Furthermore, the coated copper mesh well retains the good photothermal conversion and thermal conductivity properties of the micro SiC particles. Under NIR irradiation, the surface temperature of the coated copper mesh placed on the ice layer can increase by 35.3 °C in 220 s, so that it can rapidly melt the accumulated frost and ice layer on the inner wall of the refrigerator. The presented flexible photothermal icephobic copper mesh exhibits enormous potential when applied to remove ice from apparatus that is accessible, such as road, overhead transmission lines and power networks owing to its flexibility, economy, and high energy efficiency.

A new method for transforming common polymers into superhydrophobic conductive surfaces, with both a high static water contact angle (approximately 160 degrees) and a low sliding angle (2.0 degrees-4.5 degrees), and a low sheet resistance on the order of 10(1)-10(3) ohms/sq is presented. A layer of multiwalled carbon nanotubes (MWNTs) is first distributed on the surface of a polymer substrate, then by a single step of pressing, the MWNTs are partially embedded inside the substrate surface and form a superhydrophobic coating with a "carpet-" or "hair"-like morphology. The infiltration of polymer melts into the porous MWNT layer follows Darcy's law, and the pressing time greatly influence the morphology and superhydrophobicity. Moreover, the coating can be electrically heated by 20-70 degrees C with a voltage as low as 4-8 V at an electric energy density below 1.6 J/cm(2) and therefore can be used for deicing applications. Hydroxylation and fluoroalkylsilane treatment can greatly improve the stability of the superhydrophobicity of MWNTs. This method is convenient and applicable to a variety of thermoplastic polymers and nonpolymer substrates coated by silicone rubber.