Frosting Behavior of Superhydrophobic Nanoarrays under Ultralow

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Frosting Behavior of Superhydrophobic Nano-arrays Under Ultra-low Temperature Wenwen Zhang, Shanlin Wang, Zhen Xiao, Xinquan Yu, Caihua Liang, and Youfa Zhang Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.7b01418 • Publication Date (Web): 22 Aug 2017 Downloaded from http://pubs.acs.org on August 24, 2017

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Frosting Behavior of Superhydrophobic Nano-arrays Under Ultra-low Temperature Wenwen Zhanga, Shanlin Wanga, Zhen Xiaoa, Xinquan Yua, Caihua Liangb, Youfa Zhanga,* a

Jiangsu Key Laboratory of Advanced Metallic Materials, School of Materials Science and Engineering, Southeast University, Nanjing 211189,P. R. China b

School of Energy and Environment, Southeast University, Nanjing 210096, P. R. China

ABSTRACT Retarding and preventing frost formation at ultra-low temperature has an increasing importance because of a wide range of applications of ultra-low fluids in aerospace and industrial facilities. Recent efforts for developing anti-frosting surfaces have been mostly devoted to utilizing lotus-leaf-inspired superhydrophobic surfaces. Whether the anti-frosting performance of superhydrophobic surface is still effective under ultra-low temperature has not been elucidated clearly. Here, we investigated the frosting behavior of a fabricated superhydrophobic ZnO nano-arrays under different temperature and different environment. The surface showed excellent performance in anti-condensation and anti-frosting when the surface temperature was ~-20 ℃ . Although the frosting event inevitably occurs on all surfaces if decreasing the temperature to -50~-150℃,the frost accumulation on the superhydrophobic surfaces always less than the untreated surfaces.Interestingly, the frost layer detaches from the surface within a short time and keep the surface drying in the very beginning of defrosting process. Further, there is no frost formation on the surface at -20℃ during 10 min testing when blowing compressed air and spraying methanol together or spraying methanol individually. It can reduce the height of the frost layer and increases the density when spraying methanol at -150℃. Furthermore, the frost crystals on the upper surface can been blown away due to the low adhesion of ice or frost. It provides a basic idea for solving the frosting problem under ultra-low temperature while combined with other defrosting method. KEYWORDS: Superhydrophobicity, Anti-frosting, Ultra-low temperature, Airflow shear, Spraying methanol 1

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1.INTRODUCTION Frosting usually causes inconvenience for the daily life of human beings and sometimes leads to serious economic and safety problems on facilities such as aircraft, heat exchangers and power lines1-4. Similarly, the equipment or parts for storage, transportation or transmission of liquidus helium, hydrogen, nitrogen or oxygen operate at ultra-low temperature, definitely having serious frosting behavior. Current active ice-mitigation methods include chemical treatment using chemicals(e.g. glycol, salts and organic liquids) or physical treatment (e.g. air-impact and mechanical vibration) to remove formed frost layers5-7. Unfortunately, these conventional methods are often inefficient, energy-consuming, high-cost, or environmentally harmful. To conquer these problems, the development of environmentally harmless, economical and efficient strategies for anti-frosting is an urgent need, especially in the case of ultra-low temperature. Recently, many researches have shed light on some promising bio-inspired anti-frosting strategies. Among them, it can be divided into two categories, the liquid infused porous surface (SLIPS) and the superhydrophobic surfaces8-14. The SLIPS surfaces inspired by the Nepenthes pitcher plants can significantly reduce frost adhesion because of the trapped lubricate oil in the surface textures. As such, frost could be shed off by an action of wind or its gravity. However, it cannot delay frost formation and loss effects once the trapped oil faded15. Superhydrophobic surfaces are good candidates to solve the frosting problem. The trapped air in the surface textures endow them extremely low adhesion to water and subsequently enables effective removal of impacting and condensed water droplets before freezing16-32. Recently, the surfaces with superhydrophobic arrays have been found to show excellent anti-frosting behavior because of the self-jumping behavior of condensates, for example, Wang et al18 showed that it took about 1h for the superhydrophobic hierarchical micropore arrays to be covered by frost due to the effective self-removal of condensed microdroplets, and as compared to 8 and 14min of the normal aluminum surface and the nanostructured aluminum superhydrophobic surface at -15℃, respectively. However, most of the frosting experiment were performed at -1℃ to 2


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-20 ℃ . To date, there is few report about the anti-frosting properties of superhydrophobic surfaces under ultra-low temperature even at -150℃. It is still a puzzle whether the superhydrophobic surface has the performance of anti-frosting. Herein, we investigated the frosting behavior of a fabricated superhydrophobic ZnO nano-arrays under different temperature and different environment. And the temperature of -20℃, -50℃, -100℃ or -150℃ were selected as the experimental gradient. The frosting characteristics of different surfaces were compared by collecting the frosting process, defrosting process and the amount of formed frost. Furthermore, the frosting environment of blowing compressed air and spraying methanol together or individually were created. The process of frosting at ultra-low temperature surface under different environments was also studied. It provides a basic idea for solving the frosting problem under ultra-low temperature while combined with other defrosting method. 2.EXPERIMENTAL SECTION 2.1 Material. Zinc acetate dihydrate (Zn(CH3COO)2·2H2O, A.R., Xilong Chemical Co., Ltd., China), Ethanol were all purchased from Sinopharm Chemical Reagent

Co.,

Ltd.,China.

(CH3OCH2CH2OH,A.R.Sinopharm

Ethylene

glycol

Chemical

Reagent

monomethyl Co.,

Ltd.,

ether China).

Ethanolamine (NH2CH2CH2OH, A.R., Shanghai Lingfeng Chemical Reagent Co., Ltd., China). Polyethylene glycol 4000 (HO(CH2CH2O)nH, A.R.,Guangzhou Guanghua

Chemical

Factory

Co.,

Ltd.

China)

Zinc

nitrate

hexahydrate

(Zn(NO3)2·6H2O, A.R., Xilong Chemical Co., Ltd., China), Potassium hydroxide (KOH,

A.R.,

Sinopharm

Chemical

Reagent

Co.,

Ltd.,China),

Tridecafluoro-1,1,2,2-tetrahydrooctyl)triethoxysilane (HDFTES, Sicong Reagent Co., Ltd., China). Methyl alcohol (CH3OH, A.R., Sinopharm Chemical Reagent Co., Ltd.,China). 2.2 Fabrication of ZnO Seed Layers on nickel alloy plates. Seed layers were fabricated on nickel alloy substrates (size: 20mm*20mm*1mm) by modified sol−gel spin coating and the rapid thermal treatment. Prior to the fabrication, the substrates were thoroughly cleaned. the specimens were cleaned ultrasonically in acetone, 3


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ethanol and deionized water for 10min, respectively, then dried with flowing air. The precursor concentration of zinc acetate dihydrate in the ethylene glycol monomethylether solution was 0.5M. Ethanolamine was used as the stabilization reagent, and an appropriate amount of water was added to adjust the hydrolysis of zinc acetate. After forming a yellowish transparent sol and aging for 24h, an appropriate amount of polyethylene glycol 4000, which acts as a surfactant, was added to the sol and stirred with a magnetic stirrer at 60°C for 30 min, the final sol was achieved. The sol was spun onto the substrates at a speed of 600 rpm for 15s and then 3000rpm for 20s at room temperature, then, the sol film was dried by a cold air blower to remove the residual solvent. The procedures from coating to drying were repeated three times to ensure a complete and uniform coverage of ZnO seeds. At last, the wet films were carefully put into an argon atmosphere furnace horizontally and keep at 350°C for 10min. 2.3 Growth of ZnO Nanocone/Nanorod Arrays. First, the growth solution, 0.25M [Zn(OH)4]2−, was prepared with the molar ratio of zinc nitrate hexahydrate to potassiumhydroxide (KOH) of 1:8. Second, the seeded nickel substrates were floated in the growth solution, the object surface had to beput downward, and then the system was sealed in a beaker. Third, the growth system was put into an electrothermostatic water cabinet, and the growth temperature and time were set at 35°C and 6h, respectively. Finally, the samples were taken out and rinsed with deionized water and ethanol in sequence and dried in the oven at 80°C for 1 h. 2.4 Surface modification. After dried in oven, the samples were put into vacuum oven with 0.3mL Tridecafluoro-1,1,2,2-tetrahydrooctyl)triethoxysilane at 100℃ for 12h. then take out the samples for subsequent testing. 2.5 Characterization. Scanning electron microscopy (SEM) images were taken by a Sirion field-emission scanning electron microscope (FEI) at 20kV. The water contact angles and the sliding angles on the samples was measured by a CA System (OCA15Pro, Dataphysics) at the ambient temperature and the volume of droplets was 5 µL and 10 µL, respectively. An average value was obtained by measuring the same sample at least three times. The photographs of each samples were recorded by the 4


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digital camera (Powershot SX60 HS, Canon). Sequential images of the dynamic water droplets impacting the surface was recorded by a high-speed camera with 5000 frames per second. (Fastcam Mini UX100, Photron). And The optical images of the frosting on the untreated surface sand the superhydrophobic surfaces was recorded by a stereomicroscope (Zoom 6000, Navitar). The amount of the formed frost on the surfaces was measured by a laboratory electronic balance (Secura124-1 CN, Sartorious). Futher, the samples were fastened on a Peltier stage (-30℃~150℃) with the temperature of 2ºC for condensation experiments in a controlled ambient temperature of ~16ºC and relative humidity of ~60%. And the samples were fastened on a Peltier stage(see Figure S4) with the temperature of -20℃ for frosting experiments in a controlled ambient temperature of ~25℃ and relative humidity of ~55%. As for the frosting experiments under ultra-low temperature even at -150℃ were investigated by using the homemade cooling stage. (see Figure S7). The condition of airflow shear was achieved by the air compressor (500W-8L, OTS) and spray gun (W-101, ANEST MATA). And the speed of airflow was control at 8~10m/s which was measured by the anemometer (AR866, Smart Sensor). Furthermore, the condition of spraying with methanol was achieved by the mini air compressor (601G, U-STAR) and air brush (S-130, U-STAR). And the spraying flow control at 0.093g/s, and speed was controlled at 1.5m/s. The ultralow-room temperature stability of those superhydrophobic surfaces were investigated by immersed the surface into liquid N 2 for 20min, then take out and store at room temperature for 10 minutes as a cycle. And the cycle of frosting-defrosting test was carried at temparature of -20℃, and frosting time is 10 min. The defrosting process was controlled at 40℃ for more than 10min. 3.RESULTS AND DISCUSSION 3.1 Morphology and Superhydrophobicity of As-Fabricated Surfaces. The schematic illustration of the preparation process are presented in Figure S1. Highly oriented ZnO nanorod arrays were grown on nickel alloy plates using a two-step process, combining seeding fabrication by sol−gel spin coating and the rapid thermal treatment and nanorod array growth by a wet chemical growth method

33, 34

. The

growth methods and more details were showed in supporting information. The surface 5


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morphologies of the as-prepared surfaces were investigated using scanning electron microscopy. As showed in Figure 1(a), the surfaces were covered with highly uniform and aligned ZnO rods and oriented perpendicularly to the substrate. And the rods are typically 800~1000 nm in length, 20~50 nm in diameter at their top parts, and 40~70 nm in diameter at their bottom parts. To render it superhydrophobic, a coating with low surface energy was applied. All the water SCAs greater than 158°and RAs less than 3°. The digital photograph of water droplet on this surface was showed on Figure S2. It revealed that all of the water droplets floating on the as-prepared surface with an approximately spherical shape. As showed in Video S1 (see Video S1 in the Supporting Information) the water drop can easily rolls off when the surface was tilted by 5.0°. And Sequential images of the dynamic 20µL water droplets impacting as-prepared surface from a 10 cm height were showed in Figure 1(b) and Video S2 in the Supporting Information. The droplets able to fully retract and bounce from the surface after 10 ms when the droplet first touched the surface. It is well-documented that the as-prepared surfaces with an extremely low adhesive.3 3.2 Condensation Characteristice. Coalescence-induced self-propelled jumping by condensate droplets that occurs on the superhydrophobic surface was considered to be a key feature to prevent frosting. We investigates the motion states of condensed micro-drops on as-prepared surface (Figure S3 in the Supporting Information). We found that the ZnO superhydrophobic surfaces stays in a dropwise condensation stage and 97% of the condensed droplets with diameters below 10µm within 10min (Figure S3(e) in the Supporting Information). In contrast, the surface was keep in the filmwise condensation on untreated surfaces and the diameters of drops increased continuously (Figure S3(c) and (d) in the Supporting Information). As showed in Figure 2(a), the coalescence and vanishment processes of multiple condensed microdrops without any external force on as-prepared surface placed horizontally. Condensed microdrops can self-remove by coalescence-induced out-of-plane jumping with the diameters less than 50µm within 0.1s, powered by excess surface energy released from mutual coalescence. And the side-view (Figure 2(b) and Video S3 in the Supporting Information) also can prove the coalescence-induced self-propelled jumping events 6


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can continuously occur on the as-prepared superhydrophobic surface. 3.3 Anti-frosting Characteristics Under Static Environment. We systematically studied the time evolution of condensation frosting dynamics on the as-developed superhydrophobic surfaces. Initially, we put the sample horizontally on the cooling stage with a preset temperature of -20℃(Figure S4). As showed in Figure S5(b), the condensed microdrops are keep approximately spherical shape on the ZnO superhydrophobic surface. The condensate droplets growing over time and constantly departing from the surface at an average diameter of ~30µm. It is found that the droplets can maintain the liquid state within 5min, where no frost crystals fromation. As time go on, we found that the condensed microdrops began to freeze at time of 7min. Further, the droplet freezing primarily begins from the outer edge corners of the substrate owing to its geometric singularity and low free energy barrier for heterogeneous nucleation(Figure S6 in the Supporting Information). The frozen droplet sprouts dendritic ice crystal grew towards the surrounding unfrozen liquid droplets. And as the refrigeration time extends to 10min, the surface was covered completely by frost crystals (see Figure S5(b) in the Supporting Information). In contrast, condensed microdrops on the untreated surface freeze randomly within less than 1min once the substrate pasted into the cooling stage. Subsequently, frost crystals can grow over the entire surface (see Figure S3(a)). Secondly, the frosting process at the temperatures of -150℃ also have been investigated by using the homemade cooling stage( Figure S7), As shown in Figure 3(a) and Figure 3(b), the optical images of the frosting on the untreated surfaces and superhydrophobic surfaces, respectively. It can be seen that the frosting different from the one which executed at the temperature of -20℃. Due to the large temperature difference between the surroundings and the cooling stage, the vapor will sublimation into the frost directly

35

. As a result, the surfaces were covered by hexagonal

prism-like frost crystals once the substrate paste on the cooling stage. Subsequently, frost crystals can grow over the entire surface within less than 5min. (Figure 3(c) and Figure 3(d)). However, it can obvious find that the frost crystal is smaller and frost crystal nucleation rate is significantly higher at the beginning of frosting on the 7


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untreated surfaces. And similar results was showed at temperature of -50℃(see Figure S8 in the Supporting Information) and -100℃(see Figure S9 in the Supporting Information). In order to characterize the anti-frosting properties of superhydrophobic surface at low temperatures clearly, the amount of the formed frost within 10min was investigated. As shown in Figure 3(e), the weigh of the formed frost was 0.004g/cm2 on the untreated surface, and more than 1.6 times approximately in comparison with the ZnO superhydrophobic surface. And the frost morphology evolution during the defrosting process on the untreated surfaces(see Video S4 in the Supporting Information) and ZnO superhydrophobic surfaces (see Video S5 in the Supporting Information) also been recorded. We found that the defrosting process within a relatively shorter time on the ZnO superhydrophobic surfaces, and there is no residual water. And all of the work demonstrates the superhydrophobic surface can be used for anti-frosting applications at temperature below zero even to -20℃. Meanwhile, the amount of the formed frost on the ZnO superhydrophobic surfaces was 0.0055g/cm2, and slightly less than the untreated surfaces in the same frosting period at the temperature of -150℃ (Figure 3(f)). And as the temperature decreases, the difference in the amount of frosting is smaller. Similarly, the frost morphology evolution over time after 10min freezing under the -150℃ were collected (see Video S6 and S7 in the Supporting Information), the frost layer also can detaches from the surface within a short time and keep the surface drying with very little residual water on the ZnO superhydrophobic surfaces (see Figure S10 in the Supporting Information). Therefore, these features are also important for anti-frosting in practical applications, especially under ultra-low temperature. 3.4

Anti-frosting

Characteristics

Under

Others

Environment.

The

superhydrophobic surfaces with extremely low adhesion strength have been explored by the existing literature

31, 36, 37

. The optical images of the frosting formation under

the condition of airflow shear at the temperature of -20 ℃ or -150 ℃ were investigated. As shown in Figure 4(a), frost crystals completely and homogeneously covered the untreated surface within 1min at temperature of -150℃. And the 8


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thickness of frost layer increased rapidly over time (Figure 4(c)). As a comparison, the frosting formation at the ZnO superhydrophobic surface also been captured. As can be seen from the Figure 4(b) and Figure 4(d), the surface was also covered with tiny frost crystals within 1min. Another phenomenon was also found that the frost crystals can been blown away on the upper surface (see Video S8 in the Supporting Information). Therefore, the frost layer appears rapid growth then falls off phenomenon

36

, and the

frost layer was controlled in a lower level. And similar results was showed at temperature of -20 ℃ (see Figure S15(b) and Figure S16(b) in the Supporting Information). The droplets slides away from the surface under the action of airflow shear on the ZnO superhydrophobic surfaces while the droplets grows to a certain size. However, the formation of frost crystals can not be retarded by airflow shear. Conversely, the amount of frosting has been greatly improved on the untreated surface (see Figure S15(a) and Figure S16(a) in the Supporting Information). From the previous results, we found that the frosting event still inevitably occurs on the junction of the nanostructured surface. How to reduce the height of frosting layer is a matter of concern. We have further demonstrate the function of non-condensable gas during the frosting. And methanol was selected as the non-condensable gases in the experiment and mixing by way of spraying( Figure S11). As shown in Figure S14(b), the spherical condensate droplets growing over time and maintain their liquid state within 10min at the ZnO superhydrophobic surfaces. Due to the instantaneous Cassie state of the condensed droplets, the contact area is small which have large thermal resistance. Furthermore, due to mixing of methanol, the freezing point of the condensed droplets reduced considerably (see Figure S13(b) in the Supporting Information). However, condensed microdrops to the untreated surfaces freeze randomly within less than 3min at the temperature of -20℃(see Figure S14(a) in the Supporting Information). And the surface has been covered with frost crystal after 10 min(see Figure S13(b) in the Supporting Information). The optical images of the frosting in the case of spraying with methanol at temperature of -150℃ were shown in Figure 5(a) and (b), the frost crystals formed on surfaces instantly, both at the untreated surfaces and ZnO superhydrophobic surfaces. 9


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Compared with the previous results, the density of the formed frost crystals is greater and the frost crystal is more small (Figure 5(c) and (d)). The top of the crystal frost will melted into water and penetrated into the surface while methanol was mixed, which making the crystal density increasesed. We also found that there were no significant differences in the morphology and weight of frosting in the case of spraying with methanol on both surfaces. Therefore, the trends of SCAs and RAs on the surfaces with change of methanol content were shown in Figure 7(d). With increasing methanol content, the contact angle of the water decrease sharply, and when the content exceeds 50%, the ZnO surface lost its superhydrophobicity. Similarly, the picture of the defrosting can be seen that the superhydrophobic surface has been wetted by the defrosting water (see Figure S17 in the Supporting Information). The optical images of the frosting formation under the condition of airflow shear and sprayed with methanol also been collected. As shown in Figure S18(a), there will be a large amount of frost crystals formed on the untreated surface within 3min at the temperature of -20 ℃ . Surprisingly, the condensed droplets on the ZnO superhydrophobic surfaces did not freeze within 10min, and the coverage ratio of water droplets is also very low (Figure S18(b) and Figure S19(b)). As shown in Figure 6(a) and Figure 6(c), the surface was covered with fine frost crystals immediately. With the extension of time, there are enormous frost crystals appear on the untreated surface at the temperature of -150℃, but the height of the frost crystals is reduced to a great extent compared to the airflow shear alone. The ZnO superhydrophobic surfaces have similar frosting process under this condition (Figure 6(b) and Figure 6(d)), however, the number of large frost crystals on the surface fall vertically. In order to characterize the anti-frosting performance of superhydrophobic surfaces under ultra-low temperature intuitively, the frosting weight after 10min at various environments was collected. As shown in Figures 7(c), It can be clearly seen that the amount of frosting deposited on the ZnO superhydrophobic surface is always lower than the untreated surface under the same conditions.

10


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3.5 Thermal Stability. Thermal stability is a critical factor for extensive application superhydrophobic coating, especially applied to the anti-frosting surfaces under ultra-low temperature. We designed and characterized heat cycle experiments, containing ultra-low-room temperature, and frosting-defrosting, to evaluate the environment adaptability of the ZnO superhydrophobic surfaces. As shown in Figure 7(a) and (b) is the change trends of SCAs and RAs on the surfaces against heat cycle times, suggested that the superhydrophobicity has not yet been changed after 30th cycle of ultralow-room temperature, or after 14th frosting-defrosting test, which shows extremely durable under ultra-low temperature. CONCLUSIONS In summary, we investigated the frosting behavior of a fabricated superhydrophobic ZnO nano-arrays under different temperature and different environment. The surface showed excellent performance in anti-condensation and anti-frosting when the surface temperature was ~-20℃. Although the frosting event inevitably occurs on all surfaces if decreasing the temperature to -50~-150℃,the frost accumulation on the superhydrophobic surfaces always less than the untreated surfaces.Interestingly, the frost layer detaches from the surface within a short time and keep the surface drying in the very beginning of defrosting process. Further, there is no frost formation on the surface at -20℃ during 10 min testing when blowing compressed air and spraying methanol together or spraying methanol individually. It can reduce the height of the frost layer and increases the density when spraying methanol at -150℃. Furthermore, the frost crystals on the upper surface can been blown away due to the low adhesion of ice or frost. The experimental results also show that the ZnO superhydrophobic surface has extremely durability under ultra-low temperature. Therefore, we provides a basic idea for solving the frosting problem under ultra-low temperature while combined with other defrosting method.

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Figure 1(a) The low and high magnified SEM images of as-prepared surface, respectively. And the first illustration is the photograph of water droplet on the ZnO surfaces. All the water SCAs greater than 158°and RAs less than 3°. The second inset reveals the nano-arrays shape from tilted 45°view. (b)Time-lapse photographs of water droplets bouncing on the superhydrophobic surfaces. Droplet sizes~25µL, impacting as-prepared surface from a 15cm height at speed of 1.73m/s. The contacting time between the droplet and the surface from encounter to separation is about 10 ms and the droplet completely leaved the surface without wetted.

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Figure 2 Optical images showing the coalescence-induced self-removal of condensed microdrops on the surfaces. (a) Top-view (b) Side-view. which recorded by a high-speed camera with 5000 frames per second. Condensed microdrops can self-remove by coalescence-induced out-of-plane jumping with the diameters less than 50µm within 0.1s. (Cooling stage temperature Tc=2℃, ambient temperature Ta=16℃ and relative humidity HR =60 %, dew-point temperature Td = 9℃)

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(e)

(f)

Figure 3 The optical images and digital photograph of the frosting on different surfaces under the condition of static environment. (a) the untreated surface, (b) the superhydrophobic surface, (c) the untreated surface, (d) the ZnO superhydrophobic surface (Cooling stage temperature Tc= -150℃, ambient temperature Ta=25℃ and relative humidity HR =55 %). (e) The frosting weight after 10min on different temperatures (f)The amount of frosting with the change of time at different surfaces at -150℃. The frost accumulation on the superhydrophobic surfaces always less than the untreated surfaces. And as the temperature decreases, the difference in the amount of frosting is smaller.

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Figure 4 The optical images and digital photograph of the frosting on different surfaces under the condition of airflow shear. And the speed of airflow was control at 8~10m/s. (a) the untreated surface, -150℃, (b) the ZnO superhydrophobic surface, -150℃, (c) the untreated surface, -150℃,(d) the ZnO superhydrophobic surface, -150℃. And the blue arrow in the figure represented the direction of airflow shear in the experiment. We found that the frost crystals can been blown away on the upper surface due to the low adhesion of ice or frost.

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Figure 5 The optical images and digital photograph of the frosting on different surfaces in the case of spraying with methanol. And the spraying flow control at 0.093g/s, and speed was controlled at 1.5m/s. (a) the untreated surface, -150℃, (b) the ZnO superhydrophobic surface, -150℃, (c) the untreated surface, -150℃, (d) the ZnO superhydrophobic surface, -150℃. The blue arrow in the figure represented the direction of spraying in the experiment. Compared with the previous results, the density of the formed frost crystals is greater and the frost crystal is more small.

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Figure 6 The optical images and digital photograph of the frosting on different surfaces under the condition of airflow shear and sprayed with methanol. (a) the untreated surface, -150℃,(b) the ZnO superhydrophobic surface, -150℃, (c) the untreated surface, -150℃,(d) the ZnO superhydrophobic surface, -150℃. The blue arrow in the figure on behalf of the direction of spraying operation in the experiment.

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(a)

(b)

(c)

(d)

Figure 7(a)Static contact angles and sliding anglesmeasured after immersing in liquid nitrogen for 20min. (b) Static contact angles and sliding angles after treated at a series of cycle of frosting-defrosting test was carried at temparature of -20℃, and frosting time is 10 min. The defrosting process was controlled at 40℃ for more than 10min. It suggested that the superhydrophobicity has not yet been changed after 30th cycle of ultralow-room temperature, or after 14th frosting-defrosting test. (c) The frosting weight after 10min at various environments, the SE expressed as static environment, the ME is mean of spraying with methanol, the AM is mean of the condition of airflow shear and sprayed with methanol and the AS indicated as the condition of airflow shear. (d) Static contact angles and sliding angles measured with change of methanol content.

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■ ASSOCIATED CONTENT Supporting Information Supplementary Text, Figure S1 to S19 and Video S1 to S8 were included. This material is available free of charge via the Internet at http://pubs.acs.org.

■ AUTHOR INFORMATION Corresponding Author Email:[email protected] Notes The authors declare no competing financial interest ■ ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Grants

51671055, 51676033), the China

National

Key R&D Program

(2016YFC0700304), the National Natural Science Foundation of Jiangsu Province (BK20151135).

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REFERENCES 1.

Yao, X.; Song, Y.; Jiang, L., Applications of bio-inspired special wettable surfaces. Advanced

materials 2011, 23, 719-34. 2.

Yao, Y.; Jiang, Y.; Deng, S.; Ma, Z., A study on the performance of the airside heat exchanger

under frosting in an air source heat pump water heater/chiller unit. International Journal of Heat and Mass Transfer 2004, 47, 3745-3756. 3.

Kreder, M. J.; Alvarenga, J.; Kim, P.; Aizenberg, J., Design of anti-icing surfaces: smooth,

textured or slippery? Nature Reviews Materials 2016, 1, 15003. 4.

Jung, S.; Dorrestijn, M.; Raps, D.; Das, A.; Megaridis, C. M.; Poulikakos, D., Are

superhydrophobic surfaces best for icephobicity? Langmuir ,2011, 27, 3059-66. 5.

Farzaneh, M.; Ryerson, C. C., Anti-icing and deicing techniques. Cold Regions Science and

Technology 2011, 65, 1-4. 6.

Parent, O.; Ilinca, A., Anti-icing and de-icing techniques for wind turbines: Critical review.

Cold Regions Science and Technology 2011, 65, 88-96. 7.

Lv, J.; Song, Y.; Jiang, L.; Wang, J., Bio-Inspired Strategies for Anti-Icing. Acs Nano 2014, 8,

3152-69. 8.

Wong, T. S.; Kang, S. H.; Tang, S. K. Y.; Smythe, E. J.; Hatton, B. D.; Grinthal, A.;

Aizenberg, J., Bioinspired self-repairing slippery surfaces with pressure-stable omniphobicity. Nature 2011, 477, 443-7. 9.

Kim, P.; Wong, T. S.; Alvarenga, J.; Kreder, M. J.; Adornomartinez, W. E.; Aizenberg, J.,

Liquid-infused nanostructured surfaces with extreme anti-ice and anti-frost performance. Acs Nano 2012, 6, 6569-77. 10. Ozbay, S.; Yuceel, C.; Erbil, H. Y., Improved Icephobic Properties on Surfaces with a Hydrophilic Lubricating Liquid. ACS applied materials & interfaces 2015, 7. 11. Pant, R.; Ujjain, S. K.; Nagarajan, A. K.; Khare, K., Enhanced Slippery Behavior and Stability of Lubricating Fluid Infused Nanostructured Surfaces. 2016, 75. 12. Liu, Q.; Yang, Y.; Huang, M.; Zhou, Y.; Liu, Y.; Liang, X., Durability of a lubricant-infused Electrospray Silicon Rubber surface as an anti-icing coating. Applied Surface Science 2015, 346, 68-76. 13. Yin, X.; Zhang, Y.; Wang, D.; Liu, Z.; Liu, Y.; Pei, X.; Yu, B.; Zhou, F., Integration of 20


Page 20 of 24

Page 21 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Self-Lubrication and Near-Infrared Photothermogenesis for Excellent Anti-Icing/Deicing Performance. Advanced Functional Materials 2015, 25, 4237–4245. 14. Rykaczewski, K.; Anand, S.; Subramanyam, S. B.; Varanasi, K. K., Mechanism of frost formation on lubricant-impregnated surfaces. Langmuir 2013, 29, 5230-8. 15. Dou, R.; Chen, J.; Zhang, Y.; Wang, X.; Cui, D.; Song, Y.; Jiang, L.; Wang, J., Anti-icing coating with an aqueous lubricating layer. ACS applied materials & interfaces 2014, 6, 6998-7003. 16. Xu, Q.; Li, J.; Tian, J.; Zhu, J.; Gao, X., Energy-effective frost-free coatings based on superhydrophobic aligned nanocones. ACS applied materials & interfaces 2014, 6, 8976-80. 17. Kim, A.; Lee, C.; Kim, H.; Kim, J., Simple approach to superhydrophobic nanostructured Al for practical antifrosting application based on enhanced self-propelled jumping droplets. ACS applied materials & interfaces 2015, 7, 7206-13. 18. Zhang, Q.; He, M.; Chen, J.; Wang, J.; Song, Y.; Jiang, L., Anti-icing surfaces based on enhanced self-propelled jumping of condensed water microdroplets. Chemical communications 2013, 49, 4516-8. 19. Guo, P.; Zheng, Y.; Wen, M.; Song, C.; Lin, Y.; Jiang, L., Icephobic/anti-icing properties of micro/nanostructured surfaces. Advanced materials 2012, 24, 2642-8. 20. Hao, Q.; Pang, Y.; Zhao, Y.; Zhang, J.; Feng, J.; Yao, S., Mechanism of delayed frost growth on superhydrophobic surfaces with jumping condensates: more than interdrop freezing. Langmuir : 2014, 30, 15416-22. 21. Chen, X.; Ma, R.; Zhou, H.; Zhou, X.; Che, L.; Yao, S.; Wang, Z., Activating the microscale edge effect in a hierarchical surface for frosting suppression and defrosting promotion. Scientific reports 2013, 3, 2515. 22. Bengaluru Subramanyam, S.; Kondrashov, V.; Ruhe, J.; Varanasi, K. K., Low Ice Adhesion on Nano-Textured Superhydrophobic Surfaces under Supersaturated Conditions. ACS applied materials & interfaces 2016, 8, 12583-7. 23. Maitra, T.; Tiwari, M. K.; Antonini, C.; Schoch, P.; Jung, S.; Eberle, P.; Poulikakos, D., On the nanoengineering of superhydrophobic and impalement resistant surface textures below the freezing temperature. Nano letters 2014, 14, 172-82. 24. Zhang, Q.; He, M.; Chen, J.; Wang, J.; Song, Y.; Jiang, L., Anti-icing surfaces based on 21


Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

enhanced self-propelled jumping of condensed water microdroplets. Chemical communications 2013, 49, 4516-8. 25. Momen, G.; Jafari, R.; Farzaneh, M., Ice repellency behaviour of superhydrophobic surfaces: Effects of atmospheric icing conditions and surface roughness. Applied Surface Science 2015, 349, 211-218. 26. Wang, Y.; Xue, J.; Wang, Q.; Chen, Q.; Ding, J., Verification of icephobic/anti-icing properties of a superhydrophobic surface. ACS applied materials & interfaces 2013, 5, 3370-3381. 27. Zuo, Z.; Liao, R.; Zhao, X.; Song, X.; Qiao, Z.; Guo, C.; Zhuang, A.; Yuan, Y., Anti-frosting performance of superhydrophobic surface with ZnO nanorods. Applied Thermal Engineering 2016, 110, 39-48. 28. Guo, P.; Zheng, Y.; Wen, M.; Song, C.; Lin, Y.; Jiang, L., Icephobic/anti-icing properties of micro/nanostructured surfaces. Advanced materials 2012, 24, 2642-2648. 29. Sun, X.; Damle, V. G.; Liu, S.; Rykaczewski, K., Bioinspired Stimuli‐Responsive and Antifreeze‐Secreting Anti‐Icing Coatings. Advanced Materials Interfaces 2015, 2.1400479. 30. Li, X.; Yang, B.; Zhang, Y.; Gu, G.; Li, M.; Mao, L., A study on superhydrophobic coating in anti-icing of glass/porcelain insulator. J Sol-Gel Sci Techn 2014, 69, 441-447. 31. Liu, Z.; Gou, Y.; Wang, J.; Cheng, S., Frost formation on a super-hydrophobic surface under natural convection conditions. International Journal of Heat & Mass Transfer 2008, 37, 412-420. 32. Shen, Y.; Tao, J.; Tao, H.; Chen, S.; Pan, L.; Wang, T., Anti-icing potential of superhydrophobic Ti6Al4V surfaces: ice nucleation and growth. Langmuir ,2015, 31, 10799-806. 33. Xia, Y. M.; Zhang, Y. F.; Yu, X. Q.; Chen, F., Direct solution phase fabrication of ZnO nanostructure arrays on copper at near room temperature. Crystengcomm 2014, 16, 5394-5401. 34. Xia, Y.; Zhang, Y.; Yu, X.; Chen, F., Low-temperature solution growth of ZnO nanocone/highly oriented nanorod arrays on copper. The journal of physical chemistry. B 2014, 118, 12002-7. 35. Hobbs, P. V., Ice physics. Oxford Clarendon Press 1974, -1, 71-72. 36. Wang, L.; Gong, Q.; Zhan, S.; Jiang, L.; Zheng, Y., Robust Anti-Icing Performance of a Flexible Superhydrophobic Surface. Advanced materials 2016, 28, 7729-35. 37. Kulinich, S. A.; Farzaneh, M., Ice adhesion on super-hydrophobic surfaces. Applied Surface Science 2009, 255, 8153-8157. 22


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Frosting Behavior of Superhydrophobic Nanoarrays under Ultralow

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