Passive Anti-Icing Performances of the Same Superhydrophobic Surfaces under Static Freezing, Dynamic Supercooled-Droplet Impinging, and Icing Wind Tunnel Tests

Mechanism and design strategy of ice-phobic surface: A comprehensive review

Ice accumulation on the surface can significantly impact the normal operation of industrial facilities and even lead to damage, resulting in economic losses. Modifying the physical structure and chemical state of the surface can effectively mitigate ice nucleation, growth, and adhesion processes. Building upon previous definitions of ice-phobic surfaces, this review provides a refined definition of ice-phobicity and reviews recent advancements in ice-phobic surfaces research. Firstly, ice-phobic mechanisms are summarized, which including principles of ice formation, theory of solid-liquid wettability of interface, and theory of solid-solid interface mechanics. Subsequently, strategies for developing near-term ice-phobic surfaces are discussed encompassing superhydrophobic surfaces, interfacial water induced surfaces, low adhesion surfaces, as well as thermal de-icing surfaces. Furthermore, a comparison is made regarding test detail definitions and commonly used test methods in researching ice-phobic surfaces to promote methodological uniformity. Lastly, the latest research findings on four distinct ice-phobic surfaces are highlighted, while also prospecting the challenges to be considered in future ice-phobic surface design.

A Self-Replenishing Lubricant Slippery Coating with Low Interfacial Toughness for Enhancing Large-Scale Deicing Efficiency

Ice accumulation on industrial and operational surfaces presents formidable challenges, necessitating effective deicing solutions for diverse applications. In this study, we develop a self-replenishing slippery lubricant (SRLS) coating designed to enhance large-scale deicing efficiency and overcome the limitations of existing low-ice-adhesion surfaces. The SRLS coating is based on a polyorganosilazane (PSZ) matrix infused with silicone oil-loaded hollow mesoporous SiO2 microspheres (SO@HMSs). These SiO2 microspheres serve as reservoirs of silicone oil, mitigating premature exudation and enhancing the coating's deicing durability in complex environments. Silicone oil functions as a plasticizer within the PSZ matrix, reducing the interfacial toughness and ice adhesion strength. By optimizing the SO@HMSs content, the SRLS-20 coating achieves a remarkably low interfacial toughness of 0.028 J m-2 and an ice adhesion strength of 8.51 ± 1.89 kPa, surpassing current state-of-the-art coatings. This reduction in interfacial toughness transitions the ice removal mechanism from strength-controlled to toughness-controlled fracture. The SRLS-20 coating maintains a constant deicing force of 15.43 ± 1.51 N cm-1 for ice layers exceeding a critical length of 12.20 cm, proving its effectiveness for large-scale deicing applications. Finite element analysis further reveals that the inclusion of SO@HMSs lowers the shear stress required for ice interface crack initiation, enhancing deicing efficiency across an extensive surface. This approach enables the development of durable, large-scale ice-phobic surfaces with low ice adhesion strength and reduced interfacial toughness, offering a robust solution for mitigating ice accumulation in industrial applications.

Durable and highly absorptive ant-nest structured superhydrophobic sponge for efficient de-icing and interfacial evaporation in polar environments

The Arctic plays a crucial role in the Earth's climate system. However, the unique geography and climate of the Polar Regions present significant challenges for anti-icing/de-icing and clean water production in the Polar Regions, and there is an urgent need for innovative materials to help personnel and instrumentation address these issues. In this work, a composite structure with both micro- and nano-rough surfaces, excellent vapour escape channels and superhydrophobic properties is developed with the design concept of an anthill delicate cross-scale multi-stacked void structure. The light absorption reaches 98% across wavelengths from 200 to 2500 nm. It also has a hydrophobicity angle of 154.5°. It de-ices within 540 s at low solar intensities and delays icing up to 5400 s at -20 °C. A vapor escape channel enables efficient interfacial evaporation, achieving a rate of 2.76 kg m-2 h in Arctic seawater. Notably, the study achieved the integrated exploration of interfacial evaporation and de-icing, converting 0.5 cm of Arctic ice into fresh water in 7200 s. Additionally, PMOS (PDA@MWCNTs@MnO2@CuO@MS) shows high durability, retaining superhydrophobicity after 200 tape strips, friction tests, and 50 icing-deicing cycles-offering a reliable solution for polar de-icing and interfacial evaporation.

Excellent Dynamic Non-Wetting Performance Induced by Asymmetric Structure at Low Temperatures: Retraction Actuation and Nucleation Inhibition

Asymmetric structures have exhibited significant advantages in regulating wetting behavior. Nevertheless, the influence of this unique structural feature on anti-icing performance remains to be further explored. In this work, static/dynamic anti-icing performance is investigated on the asymmetric superhydrophobic structures fabricated by micro-milling combined with electrodeposition. Notably, although the reduction of the degree of asymmetry increases the droplet adhesion force by augmenting the solid-liquid interface, asymmetric structures can still enable the droplet to bounce off the surface through the horizontal Laplace force generated by the contact angle difference between the two sides of the droplet. On this basis, a dynamic behavior criterion for the droplet to detach from the surface is established at low temperatures. Molecular dynamics simulation indicates that the asymmetric structure can reduce the icing probability on the precursor film by inhibiting the nucleation and growth process of water molecules, decreasing the liquid-ice interface, and reducing the adhesion under low temperatures. Generally, specific asymmetric structures with nucleation inhibition characteristics can reduce droplet adhesion and increase the driving force during the droplet retraction stage by enhancing the horizontal Laplace force, effectively improving the dynamic non-wetting performance of the surface at even -40 °C.

Multienergy Barrier Anti-/Deicing Surface with Excellent Photothermal Effect

Superhydrophobic surfaces are considered to be an effective method for anti-icing, but passive anti-icing alone is not as effective as it should be, so it is crucial to develop effective anti-icing techniques. In this study, a photothermal anti-icing structure with multienergy barriers was designed by combining active and passive anti-icing technologies and prepared by a three-step method of laser etching, hydrothermal growth of nanostructures, and chemical modification based on the Cassie-Baxter-Wenzel transition theory. The experimental results show that the static water contact angle of the prepared surface is up to 160°, the sliding angle is less than 3.6°, and the surface temperature is 25 °C higher than that of the original control group over 100 s under standard solar irradiation. The multienergy barrier design greatly prolongs the time of the anti-icing, and the durability test shows that the surface maintains superhydrophobicity even after the abrasion of sandpaper and the impact of sand. This superhydrophobic photothermal coating has great potential for anti-icing and deicing applications.

Flexible Mushroom-Like Cross-Scale Surface with Extreme Pressure Resistance for Telecommunication Lines Anti-Icing/Deicing

Ice accretion caused by freezing rain or snowstorms is a common phenomenon in cold climates that seriously threatens the safety and reliability of telecommunication lines and other overhead networks. Various anti-icing strategies have been demonstrated through surface engineering to delay ice formation. However, existing anti-icing surfaces still encounter several challenges; for example, surfaces are prone to ice-pinning formation due to the impact of supercooled droplets, which leads to a loss of anti-icing effectiveness. In this study, a mushroom-like cross-scale surface (MCS) with extreme pressure resistance and superior anti-ice-pinning property was reported. Specifically, the designed MCS, featuring multiscale microfeatures, re-entrant structure, heterogeneous sidewalls, and nanoscale particles, exhibits excellent anti-icing properties. Ice formation was determined to occur through a process involving liquid penetration, condensation, icing, and frost filling. By establishing an anti-ice -pinning model and a bubble column model, the relationship between structural characteristics and anti-icing performance was clarified. The MCS demonstrates excellent static liquid repellency (contact angle >167°) and robust dynamic impact resistance (water impact with Weber number ≥300). Furthermore, it exhibits an ultralow ice adhesion strength of 0.46 kPa. Notably, the ice adhesion strength remains below 5 kPa even after 15 deicing cycles. The anti-ice-pinning mechanism and robust icephobicity induced by the micromorphologies of MCS provide valuable insights for effective anti-icing prospects in telecommunication line surfaces and other areas in the field of information and communication technology.

A Photoelectric Synergistic Flexible Solid Slippery Surface for All-Day Anti-Icing/Frosting

The accumulation of ice on surface has caused great harm to lots of fields such as transportation or aerospace. Nowadays, various equipment or tools used in low-temperature environments, which face the risk of interface icing, usually have irregular shapes. Traditional rigid anti-icing materials are difficult to meet practical application requirements. Thus, it is crucial to develop flexible anti-icing materials that can be applied to various shape surfaces (curved surfaces, flat surfaces). In this paper, a photoelectric synergistic flexible solid slippery surface (FSSS) is prepared by using flexible basalt fiberglass cloth, flexible copper foil, flexible polyurethane/carbon nanotubes mixture, and flexible solid lubricant (the mixture of coconut wax and coconut oil). Even under harsh conditions of the temperature as low as -80 °C, the FSSS exhibits excellent all-day anti/de-icing performance whether on flat or curved surface. Moreover, the FSSS shows long-term stability both on flat and curved surface: situated in air for 60 days, submerged in water for 60 days, kept in acid environment (pH 1) and base environment (pH 13) for 30 days. Besides, the FSSS can also achieve self-healing function under -80 °C. This flexible surface provides a novel approach for de-icing/frosting of multi-shaped objects in the future.

Periodic Burst Freezing in a Water-Filled Capillary Tube

Water-filled porous structures are ubiquitous components in life sciences and engineering. At sufficiently low temperatures, the water inside the porous structures can freeze, triggering the frost heave effect and causing problems such as permafrost, frost damage, and frostbite. In this study, we report a unique pattern of frost heat release through periodic bulging and bursting at the end of a water column inside a capillary tube. When water freezes, it expands in volume and attempts to drain out. However, surface tension can hinder the flow of water, resulting in the formation of a bulge that periodically bursts when the spherical molecule reaches a critical threshold. We determined that the critical contact angle of the bulge is approximately 135°, which is balanced by the surface tension at the three-phase line of contact. The size of the bulge increases nonlinearly with the diameter of the capillary tube, while the number of periodic repetitions is inversely proportional to the tube diameter and directly proportional to the length of the water column. These findings provide insights into the interaction between surface tension and frost heave, which has important implications for the design and optimization of microfluidic devices with improved resistance to freezing.

Icing and Adhesion Behaviors on Surfaces with Varied Lattice Constants

Investigating droplet wetting and icing behavior is crucial for comprehending the principles of surface icing and the design of anti-icing surfaces. In this study, we present the evidence from molecular dynamics (MD) simulations that reveal a hitherto unreported behavior of droplet wetting and icing adhesion on surfaces with lattice constants from 2.7 to 4.5 Å. Here, we observe that the contact angles (CA) of droplets on a face-centered cubic (FCC) lattice surface consistently correlate positively with the lattice constant. Further examination of droplet behavior on an idealized crystal surface reveals that hydrophilic surfaces (e.g., CA = 85°) inhibit freezing more effectively than hydrophobic surfaces (e.g., CA = 97°). This finding contradicts the conventional explanation that hydrophobic surfaces reduce heterogeneous nucleation, thereby delaying icing. This study introduces a mechanistic explanation for the promotion of water icing by hydrophobic surfaces and offers a novel design concept for the development of anti-ice surfaces in future applications.

Multi-Scale Superhydrophobic Surface with Excellent Stability and Solar-Thermal Performance for Highly Efficient Anti-Icing and Deicing

Ice accretion can significantly impact the efficiency and safety of outdoor equipment. Solar-thermal superhydrophobic surface is an effective strategy for anti-icing and deicing. However, droplets easily turn to the Wenzel state during the icing and melting cycle processes, significantly increasing the adhesion and making the droplets difficult to remove from the surface. In this work, a triple-scale solar-thermal superhydrophobic surface is prepared on stainless steel 304 by etching, in situ oxidation, and spin-coating TiN nanoparticles for highly efficient deicing and anti-icing. The multi-scale structure enabled the droplets to recover the Cassie state completely after melting. The contact angle decreased from 162.5° to 136.7° during the icing process and gradually increased to 162.1° during the melting process. In addition, metal oxides and TiN nanoparticles enabled the superhydrophobic surface to exhibit a high solar absorptivity (α ¯ solar ${{\bar{\alpha }}_{{\mathrm{solar}}}}$ = 0.925). The synergistic effect of the superhydrophobicity and the solar-thermal performance endowed the designed multi-scale surface with excellent anti-icing and deicing performance. This work contributed to the practical development of anti-icing and deicing applications based on solar-thermal superhydrophobic surfaces.

Femtosecond laser composite manufactured double-bionic micro-nano structure for efficient photothermal anti-icing/deicing

The solar anti-icing/deicing (SADI) strategy represents an environmentally friendly approach for removing ice efficiently. However, the extensive use of photothermal materials could negatively impact financial performance. Therefore, enhancing light utilization efficiency, especially by optimizing the design of a structure with a low content of photothermal materials, has rapidly become a focal point of research. Drawing inspiration from the antireflective micro-nano structure of compound eyes and the thermal insulating hollow structure of polar bear hair, we proposed a new strategy to design a bionic micro-nano hollow film (MNHF). The MNHF was created using a composite manufacturing process that combines femtosecond laser ablation with template transfer techniques. Both theoretical simulations and empirical tests have confirmed that this structure significantly improves photothermal conversion efficiency and thermal radiation capability. Compared to plane film, the photothermal conversion efficiency of MNHF is increased by 45.85%. Under 1.5 sun, the equilibrium temperature of MNHF can reach 73.8 °C. Moreover, even after 10 icing-deicing cycles, MNHF maintains an ultra-low ice adhesion strength of 1.8 ± 0.3 kPa. Additionally, the exceptional mechanical stability, chemical resistance, and self-cleaning capabilities of the MNHF make its practical application feasible. This innovative structure paves the way for designing cost-effective and robust surfaces for efficient photothermal anti-icing/deicing on airplane wings.

A Transparent Photo/Electrothermal Composite Coating with Liquid-like Slippery Property for All-Day Anti-/De-Icing

A photo/electrothermal surface can convert sunlight and electricity into heat to solve icing problems. The combination of active photo/electrothermal surfaces with passive slippery surfaces provides a highly efficient strategy for all-day anti/deicing. However, the lack of transparency remains a primary impediment to the widespread application of these anti-icing measures in photovoltaics, windshields, and other fields. Herein, we report a bilayer transparent photo/electrothermal coating with a liquid-like slippery property for all-day anti/deicing. The prepared coating exhibits ultraslippery, low ice adhesion, and enhanced stability properties through covalent grafting of polydimethylsiloxane (PDMS) brushes in a cross-linked skeleton of epoxy. Moreover, the coating demonstrates a visible transmittance of up to 77% and effectively absorbs ultraviolet and near-infrared light due to the addition of ultraviolet and infrared absorbers, resulting in a temperature increase under sun illumination. The bottom indium tin oxide layer is fabricated to provide the composite coating with electrothermal capability, so that it can achieve all-weather deicing. The coupling of photo/electrothermal and slippery properties can promote the rapid removal of grown ice in a short time. The slippery properties and their exceptional durability under mechanical, optical, and thermal conditions render the composite coatings highly promising for engineering applications.

Dual-Energy-Barrier Stable Superhydrophobic Structures for Long Icing Delay

Using superhydrophobic surfaces (SHSs) with the water-repellent Cassie-Baxter (CB) state is widely acknowledged as an effective approach for anti-icing performances. Nonetheless, the CB state is susceptible to diverse physical phenomena (e.g., vapor condensation, gas contraction, etc.) at low temperatures, resulting in the transition to the sticky Wenzel state and the loss of anti-icing capabilities. SHSs with various micronanostructures have been empirically examined for enhancing the CB stability; however, the energy barrier transits from the metastable CB state to the stable Wenzel state and thus the CB stability enhancement is currently not enough to guarantee a well and appliable anti-icing performance at low temperatures. Here, we proposed a dual-energy-barrier design strategy on superhydrophobic micronanostructures. Rather than the typical single energy barrier of the conventional CB-to-Wenzel transition, we introduced two CB states (i.e., CB I and CB II), where the state transition needed to go through CB I and CB II then to Wenzel state, thus significantly improving the entire CB stability. We applied ultrafast laser to fabricate this dual-energy-barrier micronanostructures, established a theoretical framework, and performed a series of experiments. The anti-icing performances were exhibited with long delay icing times (over 27,000 s) and low ice-adhesion strengths (0.9 kPa). The kinetic mechanism underpinning the enhanced CB anti-icing stability was elucidated and attributed to the preferential liquid pinning in the shallow closed structures, enabling the higher CB-Wenzel transition energy barrier to sustain the CB state. Comprehensive durability tests further corroborated the potentials of the designed dual-energy-barrier structures for anti-icing applications.

Engineered Sustainable Omniphobic Coatings to Control Liquid Spreading on Food-Contact Materials

The adhesion of sticky liquid foods to a contacting surface can cause many technical challenges. The food manufacturing sector is confronted with many critical issues that can be overcome with long-lasting and highly nonwettable coatings. Nanoengineered biomimetic surfaces with distinct wettability and tunable interfaces have elicited increasing interest for their potential use in addressing a broad variety of scientific and technological applications, such as antifogging, anti-icing, antifouling, antiadhesion, and anticorrosion. Although a large number of nature-inspired surfaces have emerged, food-safe nonwetted surfaces are still in their infancy, and numerous structural design aspects remain unexplored. This Review summarizes the latest scientific research regarding the key principles, fabrication methods, and applications of three important categories of nonwettable surfaces: superhydrophobic, liquid-infused slippery, and re-entrant structured surfaces. The Review is particularly focused on new insights into the antiwetting mechanisms of these nanopatterned structures and discovering efficient platform methodologies to guide their rational design when in contact with food materials. A detailed description of the current opportunities, challenges, and future scale-up possibilities of these nanoengineered surfaces in the food industry is also provided.

Localized in-situ deposition: a new dimension to control in fabricating surface micro/nano structures via ultrafast laser ablation

Controllable fabrication of surface micro/nano structures is the key to realizing surface functionalization for various applications. As a versatile approach, ultrafast laser ablation has been widely studied for surface micro/nano structuring. Increasing research efforts in this field have been devoted to gaining more control over the fabrication processes to meet the increasing need for creation of complex structures. In this paper, we focus on the in-situ deposition process following the plasma formation under ultrafast laser ablation. From an overview perspective, we firstly summarize the different roles that plasma plumes, from pulsed laser ablation of solids, play in different laser processing approaches. Then, the distinctive in-situ deposition process within surface micro/nano structuring is highlighted. Our experimental work demonstrated that the in-situ deposition during ultrafast laser surface structuring can be controlled as a localized micro-additive process to pile up secondary ordered structures, through which a unique kind of hierarchical structure with fort-like bodies sitting on top of micro cone arrays were fabricated as a showcase. The revealed laser-matter interaction mechanism can be inspiring for the development of new ultrafast laser fabrication approaches, adding a new dimension and more flexibility in controlling the fabrication of functional surface micro/nano structures.

Trifolium repens L.-Like Periodic Micronano Structured Superhydrophobic Surface with Ultralow Ice Adhesion for Efficient Anti-Icing/Deicing

Wind turbine blades are often covered with ice and snow, which inevitably reduces their power generation efficiency and lifetime. Recently, a superhydrophobic surface has attracted widespread attention due to its potential values in anti-icing/deicing. However, the superhydrophobic surface can easily transition from Cassie-Baxter to Wenzel at low temperature, limiting its wide applications. Herein, inspired by the excellent water resistance and cold tolerance of Trifolium repens L. endowed by its micronano structure and low surface energy, a fresh structure was prepared by combining femtosecond laser processing technology and a boiling water treatment method. The prepared icephobic surface aluminum alloy (ISAl) mainly consists of a periodic microcrater array, nonuniform microclusters, and irregular nanosheets. This three-scale structure greatly promotes the stability of the Cassie-Baxter state. The critical Laplace pressure of ISAl is up to 1437 Pa, and the apparent water contact angle (CA) is higher than 150° at 0 °C. Those two factors contribute to its excellent anti-icing and deicing performances. The results show that the static icing delay time reaches 2577 s, and the ice adhesion strength is only 1.60 kPa. Furthermore, the anti-icing and deicing abilities of the proposed ISAl were examined under the environment of low temperature and high relative humidity to demonstrate its effectiveness. The dynamic anti-icing time of ISAl in extreme environments is up to 5 h, and ice can quickly fall with a speed of 34 r/min when it is in a horizontal rotational motion. Finally, ISAl has excellent reusability and mechanical durability, with the ice adhesion strength still being less than 6 kPa and the CA greater than 150° after 15 cycles of icing-deicing tests. The proposed structure would offer a promising strategy for the efficient anti-icing and deicing of wind turbine blades.

Bouncing Regimes of Supercooled Water Droplets Impacting Superhydrophobic Surfaces with Controlled Temperature and Humidity

Superhydrophobic surfaces have shown significant potential for the passive anti-icing application due to their unique water repellency. Reducing the contact time between the impacting droplets and the underlying surfaces with certain textures, especially applying the pancake bouncing mechanism, is expected to eliminate droplet icing upon impingement. However, the anti-icing performance of such superhydrophobic surfaces against the impact of supercooled water droplets has not yet been examined. Therefore, we fabricated a typical post-array superhydrophobic surface (PSHS) and a flat superhydrophobic surface (FSHS), to study the droplet impact dynamics on them with controlled temperature and humidity. The contact time and the bouncing behavior on these surfaces and their dependence on the surface temperature, Weber number, and surface frost were systematically investigated. The conventional rebound and full adhesion were observed on the FSHS, and the adhesion is mainly induced by the penetration of the droplet into the surface micro/nanostructures and the consequent Cassie-to-Wenzel transition. On the PSHS, four distinct regimes including pancake rebound, conventional rebound, partial rebound, and full adhesion were observed, where the contact time increases correspondingly. Over a certain Weber number range, the pancake rebound regime where the droplet bounces off the surface with a dramatically shortened contact time benefits the anti-icing performance. By further decreasing the surface temperature, the pancake rebound turns into the conventional rebound, where the droplet is not levitated after the capillary emptying process. Our scale analysis indicates that the frost between the posts reduces the capillary energy stored during the downward penetration, resulting in the failure of the pancake bouncing. A droplet adheres onto the frosted surface at sufficiently low temperature, especially at larger Weber numbers, on account of the coupling influence of droplet nucleation and wetting transition.

Droplet-Driven Self-Propelled Devices Fabricated by a Femtosecond Laser

Self-propelled autonomous devices have broad application prospects in energy conservation, environmental protection, and biomedical engineering. Nevertheless, the driving force always consumes external energy or special chemicals. Here, a novel and green droplet-driven device (DDD) consisting of superhydrophilic triangles on a superhydrophobic plate is processed only by a femtosecond laser. The water droplet flows into water along the superhydrophilic channel and forms a jet to provide driving force for the DDD, whose strength can be manipulated by changing the point angle of the triangle and the volume of the droplet. By fabricating multiple or special channels, the DDD can translate and rotate along the designed track and even carry objects. This provides a new route for the fabrication of green self-propelled autonomous devices and their applications in the fields of intelligent systems and environmental protection.

Laser Interference Lithography-A Method for the Fabrication of Controlled Periodic Structures

A microstructure determines macro functionality. A controlled periodic structure gives the surface specific functions such as controlled structural color, wettability, anti-icing/frosting, friction reduction, and hardness enhancement. Currently, there are a variety of controllable periodic structures that can be produced. Laser interference lithography (LIL) is a technique that allows for the simple, flexible, and rapid fabrication of high-resolution periodic structures over large areas without the use of masks. Different interference conditions can produce a wide range of light fields. When an LIL system is used to expose the substrate, a variety of periodic textured structures, such as periodic nanoparticles, dot arrays, hole arrays, and stripes, can be produced. The LIL technique can be used not only on flat substrates, but also on curved or partially curved substrates, taking advantage of the large depth of focus. This paper reviews the principles of LIL and discusses how the parameters, such as spatial angle, angle of incidence, wavelength, and polarization state, affect the interference light field. Applications of LIL for functional surface fabrication, such as anti-reflection, controlled structural color, surface-enhanced Raman scattering (SERS), friction reduction, superhydrophobicity, and biocellular modulation, are also presented. Finally, we present some of the challenges and problems in LIL and its applications.