Anti-frosting Property Research Articles

Dual-type heterogeneous interface design enables customized tuning of dielectric parameters of multifunctional, lightweight, flexible absorbers for broadband electromagnetic wave absorption

With the boom in 5 G technology comes widespread concern about electromagnetic (EM) interference and the safe use of electronics. Conventional electromagnetic wave (EMW) absorbing materials in the form of coatings are often inflexible and poorly adapted to different EM environments. Diversified application scenarios require EMW absorbing materials with a wide absorption band and multifunctional properties. Herein, the frequency dispersion (FD) requirements of the EM parameters of the broadband absorber in different frequency bands are determined by EM simulation. Based on the dominant role of interface polarization on FD, we designed different types of heterogeneous interfaces to meet the needs of strong FD in the low-frequency band and weak FD in the high-frequency band. Through the optimized design of heterogeneous interfaces, CC@ZnO/ZnS composites exhibit excellent EMW absorption performance, achieving flexible, ultrathin (2.1 mm), ultralight (10 wt%), and broadband (7.02 GHz), which is superior to EMW absorbing materials of similar compositions. In addition, the composites have good piezoelectric/inverse piezoelectric properties, which can convert EM energy into mechanical energy while absorbing EMW, thus realizing applications in multifunctional fields such as sensors, controllers and energy converters. More noteworthy is the sample's highly efficient thermal insulation, flame retardant and anti-frosting properties, demonstrating important advantages for service in harsh environments. Therefore, CC@ZnO/ZnS composites not only have good practical application characteristics while realizing broadband absorption, but also are expected to achieve multifunctional applications in different fields.

Synergistic Effects of the Superhydrophilic and Superhydrophobic Components on the Antifreezing Performances of Latex Particles and Anti-Icing Properties of Latex Films.

The development of new materials for antifreezing and anti-icing applications is a big challenge in industry and academic area. Inspired by the antifreeze proteins, latex particles with superhydrophilic zwitterionic shells and superhydrophobic cores are synthesized by reversible addition-fragmentation chain transfer emulsion polymerization, and the applications of the latex particles in antifreezing and anti-icing applications are investigated. In antifreezing study, the critical aggregate temperature (CAT) of the latex particles decreases, and the separation of the melting and freezing temperature of ice increases with the particle concentration. Enzyme molecules can be cryopreserved in the particle solution, andtheir bioactivities are well maintained. Latex particles are casted into latex films with dynamic surfaces. Anti-icing performances, including antifrosting properties, freezing delay time, and ice adhesion strengths, are studied; and the water-treated latex films present stronger anti-icing properties than other films, due to the synergistic effects of the superhydrophilic and superhydrophobic components. In addition, latex particles with zwitterionic shells and poly(n-butyl methacrylate) cores, and latex particles with small molecular surfactant on the surfaces are synthesized. The antifreezing performances of the latex particles and anti-icing properties of the latex films are compared.

A simple strategy towards construction of copper foam-based robust superhydrophobic coating based on perpendicular nanopins for long-lasting delayed icing and reduced frosting

Icing/frosting poses a significant problem for materials used in everyday applications. In recent years, anti-icing methods utilizing superhydrophobic materials have become popular. These materials have superhydrophobic surfaces with air-solid composite structures, which can prevent icing/frosting by creating air cushions in the micro- and nano-scales of the rough structure. However, long-term protection of the substrate is challenging due to air leakage from the air cushion and the breakdown of the superhydrophobic coating. The use of superhydrophobic materials in cold environments is also greatly limited by this shortcoming. In this paper, superhydrophobic copper foam (SHS CF) was created by using electrochemical oxidation and impregnation techniques and subsequent modified by fluorosilane coupling agent on the copper foam surface to reduce surface particle activity through condensation reactions, achieving a superhydrophobicity with a water contact angle of up to 170±2°. Furthermore, gas was utilized to form a specific rough structure by combining with Cu(OH)2 micro-nanopins, leading to the development of long-lasting gas in SHS CF (LAG-SHS CF). The LAG-SHS CF exhibited impressive anti-frost characteristics, with a delayed icing time of approximately 2171 s. Notably, the SHS CF retained strong wetting capabilities and excellent resistance to abrasion, UV, acid, and alkali even after the removal of LAG, which was ascribed to the fact that the composite structure effectively reduces the solid-liquid contact area and has a high roughness. These properties provide a solid foundation for the application of LAG-SHS CF. The findings of this study contribute to the creation of new materials with anti-icing and anti-frost properties.

Fluorine-Free and Transparent Superhydrophobic Coating with Enhanced Anti-Icing and Anti-Frosting Performance by Using D26 and KH560 as Coupling Agents

Superhydrophobic surfaces with non-wetting characteristics have been considered to be potential candidates for ice/frost prevention. In this study, a transparent superhydrophobic coating was created by using a simple method that employed (3-glycidoxypropyl) trimethoxysilane (KH560) and 1,2-Bis (trimethoxysilyl) ethane (D26) as coupling agents and epoxy resin (E51) as an adhesive. The synergy between KH560 and D26 significantly improves the long-term outdoor durability, anti-icing, and anti-frosting performance of the superhydrophobic coating. The coating also has good acid and alkali resistance, UV resistance, and durability. The obtained SiO2@E51@KH560@D26 can delay the freezing time of water by 1974 s, much longer than bare glass (345 s) and also longer than the coatings with only D26 (932 s) or with only KH560 (1087 s). Moreover, the SiO2@E51@KH560@D26 showed an improved anti-frosting capability compared with the other three samples and better maintained its superhydrophobic properties at low temperatures. Our study proposes a potential method to fabricate a superhydrophobic coating with both anti-icing and anti-frosting properties.

Hydrophilic/hydrophobic poly (AA-co-BA-co-BPA) anti-fog coating with excellent water resistance and self-healing properties

Glasses such as automobile windshields, mirrors, and lampshades are prone to fogging due to temperature changes, which affects the process of use and even jeopardizes safety. Hydrophilic films can prevent the glass surface from fogging by absorbing condensation droplets. However, the anti-fog film only lasts for a short period because it will gradually dissolve with the moisture increasing, which leads to image distortion. Herein, we propose a hydrophilic/hydrophobic coating to achieve longer anti-fog persistence. The strong interface bonding of the polymer is the key to improving the durability performance of the coating. It prevents interfacial failure and folding caused by fogging conditions. In this paper, a multifunctional coating with good anti-fog and anti-frost properties was prepared using butyl acrylate (BA), acrylic acid (AA) and 4-benzoylphenyl acrylate (BPA) as the polymer monomers. The light transmission of coated glass is up to 90 % even under harsh fogging conditions. The poly(AA-co-BA-co-BPA) can be firmly bonded with the plasma-treated glass plate, which greatly enhances the durability and water resistance of the coating. After being immersed in deionized water for 60 h at room temperature, the coated glass still has a certain anti-fog effect and the light transmittance is maintained at about 85 %. In addition, the anti-fog coating has excellent self-healing properties due to the fact that the carboxyl group in AA can generate hydrogen bonding, so that it can be healed within 15 s with the help of hot water after physical damage. This anti-fog coating has great potential for application in construction, shipbuilding and other industries.

Experimental study on anti-frost property and edge effect of superhydrophobic surface with millimeter-scale geometries

Frost suppression ability and edge effect are crucial for the frost formation on engineering surfaces. However, certain fundamental aspects remain ambiguous, particularly in the context of superhydrophobic surfaces featuring millimeter-scale structures.. In this study, condensation, frosting, and defrosting experiments were conducted on superhydrophobic surfaces with multiple millimeter-scale geometries. The results indicate that condensate droplets tend to grow on the top of right-angled, semi-circular protrusions, and conical structures. In the course of frost formation, superhydrophobic surfaces with millimeter-scale structures exhibit certain anti-frost properties when compared to the non-structured superhydrophobic surface. Condensation state of droplets can be maintained for a long time on the bottom area of the grooves, creating a frost-free zone. By observing the growth of frost crystals in various regions of the millimeter structure, it has been revealed that the manipulation of water vapor contact spaces can lead to the design of anti-frost surfaces with adjustable rates of frost crystal growth. Frost formation process on superhydrophobic surfaces can generate the so-called "edge effect" and is influenced by the edge structure. Frost crystals tend to form first on conical edges due to their sharp structural features. The average height of frost crystals on 90° edges, obtuse edges, and semicircular edges is significantly lower than that on conical edges, with the reductions of 31.8 %, 28.4 %, and 14.3 %, respectively. During the defrosting process, two spontaneous methods were observed to remove the frost layer: a "hand-in-hand" manner lifting off the groove and an "airfoil retraction" contraction on the protruding structures. Regardless of the structure shape, defrosting water floats on top and falls off, allowing for rapid drying of the surface and groove. This work has broadened the understanding of frost formation and defrosting on millimeter-structured superhydrophobic surfaces, and holds potential for applications in anti-frost engineering.

Food-protecting films based on soy protein isolate and natural deep eutectic solvents: Antimicrobial and antioxidant properties

Natural deep eutectic solvents (NADES) have just recently emerged as promising plasticizers in food coating applications owing to their excellent anti-frosting properties, low cost, and biosafety. Herein, we report for the first time the use of NADES as bioactive additives of soy protein isolate (SPI) to fabricate functional packaging materials. A neoteric eutectic solvent based on choline chloride/tannic acid (ChCl/TA) and the classical ChCl/citric acid mixture (ChCl/Cit) were explored to be integrated into the protein matrix at really high ratios (150 and 200 wt%). The resulting films were characterized by assessing morphological, physicochemical, and mechanical properties, as well as antioxidant and antimicrobial activities. The films exhibited a hydrophilic surface but limited water swelling (less than 10%), suggesting the formation of a crosslinked network between NADES and SPI. The ChCl/Cit films demonstrated potent antimicrobial activity in bacterial growth inhibition assay on chicken breast as well as in agar diffusion assays with inhibition zone diameters over 20 mm for gram+ and gram-bacteria, while ChCl/TA films showed the highest tensile strength (ranging from 744 to 2740 kPa), superior antioxidant activity (DPPH scavenging activity of ≈82%), and high light barrier properties, advantageous for storing light-sensitive food products. The incorporation of high concentrations of NADES in film production provides a novel and practical approach to improving the properties of protein materials for food packaging applications.

Mechanically robust liquid-embedded coating with anti-icing/deicing durability

The slippery liquid-infused porous surface has been concerned for their excellent icephobicity. However, unavoidable lubricant consumption can result in the failure of anti-icing/deicing properties. Traditional coatings cannot escape the choice between anti-icing/deicing property and mechanical performance. This paper reports mechanically robust liquid-embedded coating (MRLC) with anti-icing/deicing durability. The MRLC is prepared by a facile one-step method via adding silica and silicone oil in the process of co-curing PDMS and epoxy resin. The prepared MRLC-5–5–80 have excellent anti-fouling, self-cleaning, anti-icing/deicing and anti-frost properties in high humidity and low temperature environment. This surface remained free of liquid residue and ice within 30 min in supercooled water droplet impact test. In addition, this coating exhibited a low τice (5.48 kPa) and excellent durability. The PDMS polymer and fumed silica serve as oil storage reservoir for the coating to ensure durability, and the anti-icing/deicing durability can be restored by self-replenishing and external-replenishing. More importantly, the coating guarantees anti-icing/deicing durability while possessing excellent mechanical robustness. The liquid repellency and anti-icing/deicing performance still prevailed after various mechanical damages. This method opens the door for production of durable and mechanically robust for various anti-icing/deicing practical applications.

A novel dual condensers heat pipe photovoltaic/thermal (PV/T) system under different climate conditions: Electrical and thermal assessment

The PV/T hybrid system has irreplaceable advantages in the comprehensive utilization of energy because of its capability to simultaneously generate heat and power. A heat pipe PV/T system is often used in cold area duo to its high energy efficiency and anti-frost properties. While most of existing systems only focus on the hot water supply, rarely involving in the function of space heating. In this paper, a novel dual-condensers heat pipe system is proposed to extend its energy supply functions and application areas. This study aims to establish a mathematical model of the proposed system, and analyze the performance of the system in different climatic region cities. Three cities in different climate zones were selected as boundary conditions for the analysis. The numerical result shows that in the hot water mode the system's electrical efficiency is 13.6%, 13.3% and 13.5%, and the total efficiency is 56.1%, 59.7% and 60.6%, respectively. In space heating mode, the system's electrical efficiency is 14.7%, 14.8% and 14.8%, and the total efficiency is 55.4%, 55.4% and 51.1%, respectively. The results confirm that the performance of the novel PV/T is steady and suitable for the cities with different environmental conditions.

Anti-icing and anti-frost properties of structured superhydrophobic coatings based on aluminum honeycombs

Superhydrophobic coatings have many potential applications in prevention of ice, frost, condensation, and corrosion due to their strong hydrophobicity and self-cleaning function. However, superhydrophobic coatings do not have ideal mechanical stability in engineering applications, and the coatings lose their superhydrophobic properties with wear. We propose an innovative combination of a macroscopic aluminum honeycomb structure with a superhydrophobic coating to prepare a mechanically stable, structured coating by a simple spraying process. The coating showed excellent performance in laboratory ice, frosting, and outdoor ice tests. Compared with common superhydrophobic coatings, the total ice-up time of single droplet was prolonged by 190 s on a platform at −15 °C because of the reduced heat transfer between the macro-honeycomb wall and the droplets. After 300 wear tests, the frosting amount increased by only 0.03 g when the platform was tilted to 60% at −20 °C and 75 ± 5% humidity. In the outdoor ice test, no large area of ice was observed on the surface. Our findings provide a new strategy for industrialization of superhydrophobic coating, and our strategy has potential applications in anti-icing and anti-condensation for electrical equipment, drag reduction, and anti-corrosion.

Investigation on self-healing, anti-fogging and anti-frosting performances of silica sol modified waterborne polyurethane coatings

In this study, a series of silica sol modified polyurethane composite emulsions were fabricated via incorporating silica sol precursor into anionic silanol-terminated polyurethane emulsion, which was obtained via three steps, including (1) reacting excess hexamethylene diisocyanate (HDI) with polybutylene glycol (PBG), 2,2-dimethylhydroxypropionic acid (DMPA), bis(2-hydroxyethyl) disulfide (HEDS) in a stepwise process using dibutyltin diacetate (DBTA) as the catalyst, (2) neutralizing the resulting prepolymer with triethylamine and end-capping with 3-aminopropyltriethoxysilane (APTES), and (3) dispersing the resulting silanol-terminated polyurethane in water under stirring. The reaction products were characterized by fourier transform infrared (FT-IR) spectroscopy, hydrogen proton nuclear magnetic resonance (1H NMR) spectroscopy, Raman spectroscopy and permeation gel chromatography (GPC). The swelling degree and gel content analysis confirmed the formation of crosslinking network in the composite coatings formed after drying the composite emulsions. The self-healing performances of the coatings were investigated by differential scanning calorimetry (DSC), dynamic thermomechanical analysis (DMA), scanning electron microscopy (SEM) and tensile mechanical tests, and the anti-fogging and anti-frosting behaviors of the composite coatings were analyzed by UV–visible spectroscopy, reflectance spectroscopy, water contact angle test and optical photometry. Based on the measurements, the self-healing process, the anti-fogging and anti-frosting mechanism were discussed. At suitable amount of HEDS, this coating exhibited excellent self-healing performances with the self-healing efficiency up to 95.9 % because of the high moving ability of the chains. After self-healing, these coatings displayed the same anti-fogging and anti-frosting properties as those before self-healing. The silica sol component was found to increasing both the polar groups and crosslinking degree, endowing the composite coating with durable anti-fogging and anti-frosting properties.

Study on strength formation and frost resistance of concrete modified by molybdenum tailings

Solid waste tailing materials from molybdenum mining in China occupy extensive land areas and threaten the health of nearby residents. To address the risk and the increasing shortage of natural construction materials, using those tailings as a construction material is a potential option for the construction industry. Modified concrete mixed with other tailings materials has been widely studied. The application of molybdenum tailings modified concrete to cold regions needs to fully consider its durability. Through the concrete cube compressive strength test and rapid freeze-thaw cycle test after different standard curing time, the strength formation process and frost resistance of molybdenum tailings modified concrete are explored. On this basis, the optimal content of Mo tailing material was determined. Results demonstrated that the compressive strength and frost resistance of Mo-tailing-modified concretes increased first and then decreased with the increase in Mo tailing content. The optimal modification effect was achieved when the Mo tailing content reached 20%. Under that circumstance, the porosity of Mo-tailing-modified concrete was at a minimum before and after the freeze–thaw cycles, thus increasing mechanical and antifrost properties significantly.

Influence of wing scales of Catocala electa Borkhason on the frosting process

The frosting processes on the wing surface before and after removing the scale of the Catocala electa Borkhauson were observed by using a self-assembled experiment device. The results showed that the formation process of frosting on the wing surface with or without scales was similar. However, the scale could affect the attachment shape of water vapour on the wing surface and the time when frost began to form. The formation time of frosting on the wing surface without scales was earlier than that on the wing surface with scales, which was about 614 s. The influence mechanism of the scales on the frosting process was analyzed from the wettability and morphology of the scales on the wing surface Catocala electa Borkhauson. The scale on the wing surface of Catocala electa Borkhauson showed superhydrophobic properties, and the scale surface had criss-cross ribs, which formed many special micro-nano spaces. Superhydrophobicity could promote the rolling of water on the scales and reduce the adhesion area between water and scale surface. The special space structure could delay the cooling of droplets on the scale surface of Catocala electa Borkhauson. The study might be helpful to design or optimize the functional surfaces with anti-frosting properties based on the structure of the scale surface.

Design of cellular structure of graphene aerogels for electromagnetic wave absorption

Lightweight graphene-based aerogels have received considerable attention in the field of microwave absorption. Nevertheless, the controlled synthesis of reduced graphene oxide (rGO) aerogels with tailored pore structures for high-performance microwave absorption is a significant challenge. Herein, pore structure manipulation of reduced graphene oxide aerogels has been realized through a freeze-thaw assembly strategy, which involves chemical prereduction, freeze-thaw, further reduction and freeze-dry processes. By adjusting the prereduction time, the ultralight (5.83 mg/cm3) and highly porous (94.9%) rGO-60 aerogel develops a uniform cellular structure that maximizes multiple reflections and scattering of electromagnetic waves among microcellular free spaces. This achieves a minimal reflection loss of −61.63 dB with an effective absorption bandwidth of 7.8 GHz for an ultralow filling ratio (0.74 wt%). The radar cross-sectional (RCS) simulation further confirms that the rGO-60 aerogel can attenuate more electromagnetic energy. Meanwhile, the excellent thermal insulating and anti-frosting properties suggest promising applications in cold and humid environments. This work shows that pore structure engineering is a promising strategy for producing lightweight and multifunctional graphene aerogel-based microwave absorbers for complex environmental applications.

Robust and Durable Superhydrophobic Polythiophene/SiO2 Coated Cotton Fabric for Versatile Oil–Water Separation

AbstractWith the development of industrialization, environmental pollution problems (e.g., oily water discharge and oil spill accidents) are becoming increasingly severe. The efficient and economic treatments for oily sewage are urgently needed and remain a huge challenge. Here, a robust and durable superhydrophobic material with the contact angle above 160° is prepared by coating SiO2 particles/polythiophene on cotton fabrics through a sol–gel process and an oxidation coupling polymerization. The polythiophene/SiO2 coated cotton fabric displays excellent resistance to ultraviolet irradiation, high and low temperatures, acid and salt solution immersion, organic solvent immersion, and good mechanical abrasion durability, antidirt and antifrost properties. The modified fabric is successfully applied as a filter to separate oil–water mixtures by gravity with high separation efficiency and excellent reusability. Moreover, superhydrophobic absorbers can be easily prepared from common 3D porous materials such as a sponge wrapped with the modified fabric for the effective collection of oil. Both immiscible oil–water mixtures and emulsions (oil‐in‐water and water‐in‐oil) can be separated even under harsh conditions (acidic solution or artificial seawater). This work provides a facile and selectable solution to treat oily sewage and leads to new ways of efficient oil–water separation.

How Frost Forms and Grows on Lubricated Micro- and Nanostructured Surfaces.

Frost is ubiquitously observed in nature whenever warmer and more humid air encounters colder than melting point surfaces (e.g., morning dew frosting). However, frost formation is problematic as it damages infrastructure, roads, crops, and the efficient operation of industrial equipment (i.e., heat exchangers, cooling fins). While lubricant-infused surfaces offer promising antifrosting properties, underlying mechanisms of frost formation and its consequential effect on frost-to-surface dynamics remain elusive. Here, we monitor the dynamics of condensation frosting on micro- and hierarchically structured surfaces (the latter combines micro- with nano- features) infused with lubricant, temporally and spatially resolved using laser scanning confocal microscopy. The growth dynamics of water droplets differs for micro- and hierarchically structured surfaces, by hindered drop coalescence on the hierarchical ones. However, the growth and propagation of frost dendrites follow the same scaling on both surface types. Frost propagation is accompanied by a reorganization of the lubricant thin film. We numerically quantify the experimentally observed flow profile using an asymptotic long-wave model. Our results reveal that lubricant reorganization is governed by two distinct driving mechanisms, namely: (1) frost propagation speed and (2) frost dendrite morphology. These in-depth insights into the coupling between lubricant flow and frost formation/propagation enable an improved control over frosting by adjusting the design and features of the surface.

A Fluoropolymer-Coated Nanometer-Thick Cu Mesh Film for a Robust and Hydrophobic Transparent Heater

To develop more effective optoelectronic devices with a transparent heater, it is necessary to investigate the droplet evaporation characteristics and wettability control on the heater surface. An optically transparent and hydrophobic amorphous fluoropolymer, Cytop, is spin-coated onto a nano-thick copper (Cu) micromesh-based transparent conductor to evaluate its performance for a high-durable transparent heater (a transmittance of 81.6% at 550 nm, a sheet resistance of 5 Ω sq–1). As the result, the thermal and chemical stabilities of the pure Cu micromesh-based transparent heater with the ∼80 nm thick Cytop layer improve without performance degradation. The evaporation time of water droplets on the surface of the hydrophobic transparent heater is noticeably delayed (about 60–130%) because the average evaporation flux of the droplet on the surface of the hydrophobic transparent heater is lower than those on the hydrophilic heater surfaces. In addition, unlike when the heater surface is hydrophilic, there is no coffee-ring effect when the heater surface is hydrophobic due to the recirculating Marangoni flow within the droplet. Further, the hydrophobic transparent heater surface exhibits excellent icephobic and antifrost properties. The results will be helpful for the further development of practical transparent heaters including self-cleaning smart windows, transparent actuators, transparent chemical and biological sensors, and transparent heating sources.

Effect of copper surface modification applied by combined modification of metal vapor vacuum arc ion implantation and laser texturing on anti-frosting property

Heat transfer deterioration due to frost accumulation on metallic surfaces provided motivation for development of protective barriers that could effectively repel water in many forms. Currently, extensive attention has focused on superhydrophobic surfaces which have been found to be effective in reducing droplets condensation and frost accumulation. The combined modification using nanosecond laser and metal vapor vacuum arc (MEVVA) ion implantation of carbon is applied to the copper surface. The results revealed that the increased proportion of carbon content contribute to the increase of surface hydrophobicity, the contact angle of the combined surface was 152.1° ± 1° and the rolling angle was 6.7° ± 1°, which exhibited a superhydrophobic character, without thermal conductivity deterioration. The processes of droplet condensation, freezing and the frosting of three kinds of surfaces (rough #1, combined surface modification #2, silanization coating #3) have been examined. The combined surface can delay the freezing process to some extent. Compared with rough copper surface, combined surface had sparse frost structure and the growth of frost could be delayed by 43% when the frost thickness was 1.5 mm. Thus, the method of combined surface shows a great advantage of frost inhibition applicability.

Facile fabrication of biomimetic liquid-infused slippery surface on carbon steel and its self-cleaning, anti-corrosion, anti-frosting and tribological properties

Herein, facile and commercial nanosecond laser treatment was utilized to fabricate biomimetic liquid-infused slippery surface on carbon steel, and its self-cleaning, anti-corrosion, anti-frosting and tribological properties were systematically analyzed. The SEM and three-dimensional morphology analysis results revealed that the laser treatment was effective in producing extreme rough, porous and multilevel surface morphology on steel substrate. After fluorination process and subsequent oil infusion, slippery surface was successfully created. Through wetting analysis, it was found that as-prepared slippery surface showed hydrophobic property with a low contact angle hysteresis, indicating that a uniform and smooth oil layer had been created. Owing to its excellent anti-wetting and insulator effects to liquid medium, slippery surface was proven to behave superior self-cleaning and anti-corrosion performances. Furthermore, slippery surface could also effectively postpone the moisture condensation, which hence endowed steel substrate with enhanced anti-frosting property. Compared with base steel, slippery surface also showed improved friction-reducing and anti-wear performances due to the lubricating effect of oil layer. Based on these results, it could expect that the prepared slippery surface is promising to expand the practical application of traditional carbon steel materials.

Understanding the frosting and defrosting mechanism on the superhydrophobic surfaces with hierarchical structures for enhancing anti-frosting performance

To ascertain the inhibiting-frost ability of superhydrophobic surfaces, the processes of frosting and defrosting were observed on four surfaces with different microstructure topography-features in this work. Comparing with the untreated hydrophobic surface, the superhydrophobic microstructure surface exhibited superior anti-frosting performance. Besides, this work demonstrated that the anti-frosting property was sensitive to surface microscopic structure, since microstructures could induce to trap air pockets underneath the droplets to produce ultra-low water adhesion and thermal insulation, resulting in a significant delay of frost formation. After frost completely being melted into pure water, the superhydrophobic surfaces significantly contributed to enhance the defrosting efficiency and the coverage fraction of remained water was only 8.5% for microblock-nanohair hierarchical structure surface. The residual droplets in Cassie-Baxter state can be facilely removed by airflow or a slight inclination, whereas the melted water mostly firmly stayed on the flat untreated surface. In addition, the comparative researches with the other structure (i.e., microblock structures and nanohair structures) surfaces further ascertained that the nanostructures on the superhydrophobic surface will contribute to the coalescence movement of microdroplets, and the primary microstructures mainly play a role in jumping or sweeping movement of the coalesced droplets.