Toward Easily Enlarged Superhydrophobic Materials with Stain

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Toward Easily Enlarged Superhydrophobic Materials with Stain-resistant, Oil-Water Separation and Anti-corrosion Function by a Water-based One-step Electrodeposition Method Huaiyuan Wang, Ziyi Hu, Yixing Zhu, Shuhui Yang, Kai Jin, and Yanji Zhu Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b04401 • Publication Date (Web): 06 Jan 2017 Downloaded from http://pubs.acs.org on January 8, 2017

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Industrial & Engineering Chemistry Research

Toward Easily Enlarged Superhydrophobic Materials with Stain-resistant, Oil-Water Separation and Anti-corrosion Function by a Water-based Onestep Electrodeposition Method Huaiyuan Wang∗, Ziyi Hu, Yixing Zhu, Shuhui Yang, Kai Jin, Yanji Zhu College of Chemistry and Chemical Engineering, Northeast Petroleum University, Daqing, China KEYWORDS: Superhydrophobic, one-step electrodeposition, water-based, surface multifunctionalization, ultrasound-assisted, scaling-up

ABSTRACT: One-step fabrication methods toward superhydrophobic (SH) coatings are recognized very cost-efficient. However, most of the emerged one-step methods rely on the organic solvents to dissolve low surface energy material (LSAM), which might bring serious environmental issue. In this work, a water-based one-step electrodeposition route was provided to obtain high-performance SH coating on various materials and output functional products like,

∗

Corresponding author. Tel.: 0086-4596503083; Fax: 0086-4596503083.

E-mail address: [email protected] (H.Y.Wang)

ACS Paragon Plus Environment

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the mesh used for oil-water separation, a self-cleaning “black board” or stain-resistant cloth, all can be prepared within 5 min. An unconventional lauric acid (LA) emulsion containing metal ions was served as the electrolyte, and with the appearance of ultrasonic field, the organic part was effectively co-deposited. The coated SH surface enjoyed excellent mechanical stability and corrosion-resistant property. Profitably, the electrolyte can be repeatedly utilized for several cycles. Besides, our experiment proved that this technique was really scalable, rendering it great potential for quantity production.

1. INTRODUCTION

In the past few decades, the synthesis of superhydrophobic (SH) surfaces occupying a water contact angle (WCA) over 150° attracts heated research. These surfaces have shown tremendous potential of self-cleaning,1-3 drag reduction,4,5 anti-icing,6 anti-corrosion,7,8 oil-water separation,912

anti-scaling13 and so on. The common fabrication routes for a SH surface including the namely

“top-down” method like chemical etching,9,14,15 anodic oxidation16 or lithography,17,18 and “bottom-up” approaches such as electrodeposition,19,20 spray coating,21,22 self-assembly method (SAM)23 and spin coating.24 Among the numerous fabrication routes, one-step methods25-28 enjoy a huge superiority of short-time available and very cost-efficient. Nevertheless, it is commonly a basic rule to use organic solvents as methanol, ethanol or ethyl acetate to dissolve the low surface energy material (LSEM) in purpose to achieve SH structure in single process. Once in scaling-up producing circumstance, the organic solvents would cause enormous environmental problem. Besides, very


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few literatures have researched into the mechanical stability of their one-step products, for it is probably more difficult to achieve a well-controlled reaction kinetic in the one-step system and the overloaded LSEM inside the structure can seriously decrease the mechanical strength and hardness. Here a water-based one-step electrodeposition route had been reported to create SH coating on various materials and output qualified multi-functional products. As the SH coating was prepared on metal substrates, the resulted surface exhibited the texture similar to that of a black board and enjoyed efficient self-cleaning property; as prepared on meshes, it can then served in efficient oil-water separation; and when prepared on soft materials like carbon cloth, it performed high resistant to water, coffee or even milk. All the products can be realized in less than 5 min. More advantageously, defect-less coating can be conveniently achieved on a sufficient large surface in a rotary drum electrodeposition manner, rendering it great potential of scaling-up that meet the requirement of large quantity production. The output coating presented an apparent nanocrystalline growing feature which was confirmed by the SEM images and XRD result. This nanoscale coating acted excellent mechanical durability that exhibited a WCA enhancing behavior even after sandpaper abrasion of an ultra-long length, as well displayed remarkable corrosion-resistant property, extensibility and bonding strength. The electrodeposition was conducted in a lauric acid (LA) emulsion containing metal ions, which was harmless to human body. With the appearance of external ultrasonic field, the LA colloids were “refined” and moderately co-deposited into the metal matrix without apparently decrease the mechanical strength of the metallic structure. FT-IR curve and DSC result confirmed the co-deposited LA appeared in the form of laurate salt. XPS spectrum indicated the strong M-O binding (M refers to the deposited alloy) between the metallic crystals and the


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carboxyl group from LA. Besides, the electrolyte displayed an impressive feature of reusable that can be repeatedly utilized for several times. It is convinced that this one-step and environmentalfriendly technique possesses broad prospect in the quantity production of oil-water separation, stain-resistant and anti-corrosion materials.

2. EXPERIMENTAL SECTION

Materials. In this work, the widely applied Ni-Cu alloy was chosen as the coated material. NiCu system was one of the most widely researched topics as films, when Ni was alloyed with Cu, it was possible to grow strain free structures based on their similar crystal structure (facecentered cubic, fcc) along with almost the same lattice parameters (approximately 2.5 % misfit).29 The nickel ions source was from the combination of nickel sulfate and nickel chloride (both purchased from Tianjin Fuchen Chemical Reagents Factory), while copper ions was supplied by copper foil as the anode. The boric acid (purchased from Shenyang East China Reagent Plant) was used to adjust solution pH value to 5. The lauric acid (LA) was a Tianjin Chemical Reagent Factory production. The micron-sized SiO2 particle (purchased from Aladdin Company, with a mean diameter of 2 µm) and saccharin sodium (from Kaifeng Xinhua Fine Chemical Factory of Pingmei Company) were added as the crystal modifier. All the reagents were of AR grade and the were summarized in Table 1. Distilled water with a resistivity greater than 18.0 MΩ⋅m was used throughout the experiment. Table 1. The Composition of the Electrolyte. Bath concentration NiSO4·6H2O

0.038~0.33 M


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NiCl2·6H2O

0.084 M

H3BO3

0.3 M

Lauric acid

2.5 mM

Saccharin sodium

4.2 mM

SiO2 particle

13.0 mM

The copper foil was served as anode while the cathode material can be varied, which were stainless steel (SS) or aluminum substrates (both were 1 mm in thickness), SS mesh (200 meshes), copper foil (0.2 mm in thickness), aluminum foil (0.1 mm in thickness) or practical tool as pocket knife, non-metallic material as carbon cloth. Preparation of Electrolyte. Before preparing electrolyte, the LA was mechanically smashed into powder beforehand, then added into the distilled water. After a 10 min sonication at the bath temperature of 40 ℃, the rest components were added and a green emulsion (see Figure 1b) achieved. Electrodeposition Procedure. All materials served as the electrodes were degreased into pure ethanol, cleaned under ultrasound environment for 10 min, followed by distilled water washing for 5 min. Specially, the metallic substrates or foils were abraded with a successive of sand papers from 400 to 1000 grit before the cleaning process. The electrodeposition set-up was displayed in Figure 1a. A built-in heater ensured the bath temperature maintained at 40 ℃. In this system, moderate ultrasonic-field with a power of 300 W and a frequency of 40 kHz was applied. The two electrodes were set face-to-face and separated by 2.5 cm. During electrodepositing, a direct current supplier (Maisen, MS605D) applied a constant voltage of 4 V. After a proper electrodeposition duration within 5 min (the electrodepositing time


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can be varied for different cathodic materials), the fabricated coating was rinsed thoroughly by distilled water and dried at room temperature for 30 min.

Figure 1. (a) The illustration of the electrodepositing set-up, where the numbered elements are: 1) direct-current power supplier; 2) copper foil as the anode; 3) cathode material; 4) build-in heater; 5) water bath; 6) iron stand and 7) ultrasound emitter. (b) The as-prepared emulsion as the electrolyte; the appearance of the coated surface fabricated (c) in the absence and (d) in the appearance of ultrasound. Scanning Electron Microscopy and Energy-Dispersive X-ray Spectroscopy. A ΣIGMA field emission gun scanning electron microscope (SEM, ZEISS, Germany) was applied for surface morphologies characterization. Before taking images, the specimens were mounted on conductive carbon adhesive tabs and were then sputter-coated with a thin layer of gold. An


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energy dispersive X-ray spectrometer (EDS) attachment was used for qualitative elemental chemical analysis. Atomic Force Microscope. The atomic force microscope (AFM, XE7, Park Company) was used to measure the surface roughness data such as average roughness (Ra) and root mean square roughness (Rq). The results were obtained by scanning a 50 × 50 µm area. Fourier-Transform Infrared Spectroscopy and Differential Scanning Calorimetry. A Tensor27 infrared spectrometer (FT-IR) was used for analyzing the existing form of LA on the surface, which was obtained by a KBr pellet technique. The differential scanning calorimetry apparatus (DSC, a NETZSCH product) was applied and the heating rate was controlled to be 10 K/min to analyze the melting behavior between the pure LA sample and the LA existed in the metallic film. X-ray Diffractometer. The crystalline structure of the sample was studied by an X-ray diffractometer (XRD, D/max2200) operating at 40 kV/40 mA. X-ray Photoelectron Spectrumscopy. The coordination between the metallic crystals and LA was studied by an X-ray Photoelectron Spectrumscopy (XPS, Thermo VG Multilab 2000 spectrometer), which was carried out by a monochromatic Al Kα X-ray source. All the core-level spectra had been referenced to C 1s neutral carbon peak at 284.8 eV. Contact Angle and Sliding Angle Measurement. The static contact angle (CA) was evaluated by a contact-angle meter (JGW-360A, Chengdeshi Shipeng Detection Equipment Co., Ltd). Sliding angle of the liquid drops was measured by gradually inclining the tilting stage of the substrate, and the recorded sliding angle was the slope of the tilting stage, on which a liquid droplet began to roll away. All the liquid droplets applied had a volume of 5 µL and the tests


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were operated at room temperature. Both wettability parameters were obtained by measuring six times in each case, with a typical averaged error of less than ±4°. Electrochemical Measurement. The electrochemical measurement was operated on an electrochemical workstation (LK 2010) in a 3.5 wt.% NaCl solution at room temperature. A classic three-electrode cell with a platinum plate (Pt) was employed as the counter electrode and a saturated calomel electrode (SCE, +245 mV vs SHE) as the reference. Linear Abrasion Tests. To exam the mechanical durability of the SH coating, a harsh liner abrasion test was conducted by adding 1.3 kPa pressure load on a coated SS substrate (1.2 × 4 cm in coating area), and then drove the substrate to slide on a 1000 grit sandpaper for up to 4 m. Bonding Strength Test. To investigate the adhesion property, the cross cut tape test was conducted according to the ASTM standard D3359-02. The coated copper foil was used for examination.

3. RESULTS AND DISCUSSIONS

3.1. Creation of Various SH Products and Their Multi-functionalization. Figure 2 displays numerous SH materials provided by this electrodepositing method. It can be concluded that scarcely any defect emerged with the increase of surface dimension or geometric complexity. When the SH coating was successfully decorated on a flattened SS substrate (see Figure 2a), it showed an apparent roughness similar to a black board, and the writing of chalk can be simply erased by running water. Noticeably, no visible surface damage were caused by the scratch of chalk. In another experiment, the coated mesh performed high-efficient oil-water separation property (see Figure 2b). Apart from that, the SH coating acted good compatibility on nonmetallic materials, where we obtained a high-performance stain-resistant carbon cloth (see


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Figure 2d and the excellent anti-fouling ability of the coated cloth showed in Figure S1). Figure 2c confirms a strong durability of the SH coating on a practical tool as pocket knife. All these SH products are able to be realized in less than 5 min.

Figure 2. Highly-performed SH products were fabricated all in less than 5 min: (a) coated SS substrates with the texture similar to that of a black board and showing the self-cleaning property; (b) coated SS mesh with the performance of oil-water separation; (c) coated pocket knife with excellent mechanical stability and (d) stain-resistant cloth. The inserts in (b1) are the water contact angle (WCA) of bare and coated mesh. (c2) reveals that the coated knife was used to


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slice a piece of eraser with a sectional area of 1.6 × 1.6 cm, (c3) indicates the WCA change after each slicing cycle. (d2) exhibits the sliding angles for different types of liquid on the SH cloth. 3.2. Examination of Scaling-up Property. Since the coating is characterized in showing no constraint on various sorts of substrates while all can be available immediately, it is expected if this method is able to achieve SH products on a sufficiently enlarged scale. Figure S2 demonstrates that an uniform SH coating can be prepared on the inner wall of a large-area Ushaped workpiece, without any loss of superhydrophobicity happened at the 90° corner. In another test, a rotary drum device (see Figure 3a) was designed allowing the electrodeposition to be implemented in an incomplete immersion way, which won a huge superiority of achieving very large-area product at a low raw material consumption. A 50 × 4.5 cm aluminum foil was glued on the outer side of rotary drum to be coated (see Figure 3b), and by searching for a optimized experimental condition, the rotating speed (n) of the drum was set to be 1 r/min. A central angel (θ) of 100° allowed an immersion length of 14 mm. After a 40 min experiment, a SH surface in an uniform black color realized (see Figure 3c and 3d). It is convinced that the one-step technique is very scalable.


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Figure 3. (a) The illustration of the rotary drum device used for very large area coating, and the numbered components are: 1) surrounded aluminum foil, 2) electro-brush, 3) rotary drum, 4) transmission, 5) electrolyte bath and 6) anodic copper foil. The appearance of aluminum foil (b) before and (c) after the electrodeposition process; (d) the fabricated large-scale SH coating with good water repellency. For another part, the reusability of the electrolyte was examined. In this test, a 100 mL prepared electrolyte was prepared to undergo several electrodeposition cycles. In each cycle the coating was fabricated on a bare SS substrate from this electrolyte, leaving a 1.2 × 4 mm immersion area. Then after resting for 1 h, the solution was picked up for another electrodepositing cycle. As reveals in Figure 4, the repeatedly used electrolyte was capable to realize qualified SH coating over a hydrophilic SS surface even after 4 cycles (a typical water drop image on a bare SS surface is displayed in Figure S3).

Figure 4. The WCAs of the coatings fabricated from repeatedly used electrolyte. The inserts show the coated surface in the first and the last electrodeposition cycle.


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3.3. Surface Morphology and Characterization. The SH film fabricated on SS substrates were used for surface characterization. The experimental condition was controlled to be 0.11 M nickel sulfate, 2.5 mM LA, and an electrodeposition time of 8 min was chosen to obtain a proper thickness. During our experiments, it discovered a striking contrast between the appearance of coated surfaces that electrodeposited with and without ultrasound irradiation (see Figure 1c and 1d). In the absence of ultrasonic field, many accumulated LA particles can be observed on the coated surface that were being embedded or adsorbed, resulted in very loose surface structures. Oppositely, it appeared very compact and defect-less products in the presence of ultrasound. Conclusively, the ultrasound irradiation acted a special effect to “refine” the size of LA particles that were going to be co-deposited. Figure 5a and 5b are the SEM images of the surface fabricated under ultrasound-assisted condition, exhibiting clearly the existence of the micro/nanobilayer with high density. The metal structure appears mainly in the form of nanoscale crystals enjoying a diameter of about 200 to 300 nm, and these nanocrystals organize into several macro-sized structural units. Advantageously, no visible cracks or other defect has been detected on the metallic surface. Figure 5c displays the cross-section view of the metallic film, which enjoys a thickness of over 10 µm corresponding to a electrodepositing time of 8 min. Additionally, the surface roughness data has been investigated by AFM profile as shown in the insert of Figure 5a. It is found that an average roughness (Ra) of 0.353 µm and a root mean square roughness (Rq) of 0.449 µm received after electrodeposition. EDS analysis is used in order to investigate the surface element composition. As shown in Figure 6a, the EDS spectrum of the superhydrophobic surface reveals the existence of C and O,


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demonstrating the co-deposition of lauric acid. Fe element that being detected is coming from the SS substrate. The element composition summary is in Table 2.

Figure 5. SEM images at the magnification of (a) ×8,000; (b) ×20,000 and (c) the cross-section view of the SH film. The insert of (a) provides the typical AFM image (50 × 50 µm) of the surface. Chemical composition analyses of the surfaces are studied by FT-IR, Figure 6b plots the FT-IR spectrums of the pure lauric acid and the sample from the as-prepared film. The curve of pure LA illustrates the presence of peak at 1701 cm-1 from the free COO band before the electrodeposition process, while which disappears in the curve below, replaced by a new band at around 1556 cm-1. This is related to the coordinated COO functional groups and thus claims the formation of laurate, which is from a reaction between LA and metal ions. Figure 6c provides the differential scanning calorimetry (DSC) spectrum to match and support the FT-IR results. It shows that the melting of pure LA sample can be detected at about 45-55 ℃ but no obvious phase change for the film sample below 200 ℃. This can be concluded that the LA existed fully in the form of laurate salt, enjoying a stronger bonding and a much higher melting point. Figure 6d is the typical XRD pattern of the film. In correspondence with the JCPDS database, obvious peaks at 44.5°, 51.8° and 76.4° each assigns to the pure face-centered cube (fcc) nickel plane of (111), (200) and (220) orientation. Scarcely any peak of Cu crystal can be observed under such


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situation due probably to the comparatively low reduction amount or the amorphization of the alloyed Cu. It has been calculated that the peak intensity ratio of (111), (200) and (220) is 2.54:1:1. The preferred crystal growth along the (111) orientation in contrast to the normal (200) plane oriented Ni film reveals the typical growth of nanoscale metal crystals. In addition, the investigation by XPS spectrum demonstrates clearly the existence of Ni, Cu, C and O elements (Figure 7a). The high-resolution spectra for Ni element in Figure 7b shows the typical Ni 2p3/2 peak at 852.0 eV, while another two strong peaks each at 855.1 and 869.1 eV are discovered, which should be assigned to Ni-O bond and thus confirm the coordination between Ni and COO group from LA. The similar result can be concluded for Cu element. As in Figure 7c, the peak at 931.7 and 951.4 eV each ascribed to Cu 2p3/2 and 2p1/2, two more peaks at 943.0 and 961.4 eV should be Cu-O coordination. Conclusively, the COO polar group of LA can strongly interact with the Ni-Cu alloy, therefore ensure the stability of the one-step reactant.

Figure 6. (a) The EDS results of the SH film; (b) the DSC and (c) the FT-IR analysis between the pure lauric acid and the SH film; (d) the XRD spectrum of the SH coating sample.


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Table 2. A Summary of Element Composition in EDS Research. Element

Wt %

Ni

65.07

Cu

25.65

C

5.11

O

2.52

Fe

1.65

A side reaction of hydrogen evaluation would occur on the cathode surface during electrpdeposition process, thus the major reaction processes of the cathode side can be formulated as follows: Ni2+ + 2e-→ Ni↓

(1)

Ni2+ + 2CH3(CH2)10COOH→ Ni[CH3(CH2)10COO]2↓ + 2H+

(2)

Cu2+ + 2e-→ Cu↓

(3)

2H+ + 2e-→ H2↑

(4)

Figure 7. (a) XPS full spectrum of the coated surface; the high-resolution XPS spectra of (b) Ni and (c) Cu species. 3.4. Schematic of the Electrodeposition Mechanism. The detailed performance of the LA colloids in the depositing process, as a significant case in our study, has been discussed. Former


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study discovered that the long-chain fatty acid would disperse in water as micro-scale colloids.30 The experimental phenomenon shows in Figure 1c confirms that the direct electrodeposition in this sort of emulsion may result in quite loose structure. Thus, the effect of the added ultrasonic field can be summarized in that it “refined” the size of LA that are going to be co-deposited. Ultrasound is acknowledged to generate acoustic cavitation phenomenon inside the liquid environment, in which circumstance many micro-sized bubbles appeared. Besides, as surface tension of the liquid is high, the air nucleates are tent to be formed previously at the solid-liquid interface.31,32 Thus it is convinced that the surface of dispersed LA colloids can easily meet bubble nucleation. By creating highly active region around the suspended particles, these dynamic bubbles will greatly change the existing form of the saturated fatty acid. The hydrophobic colloids might disintegrate and show a strong tendency to diffuse into the gaseous bubble interior, orienting themselves in the bubble-liquid interfacial region with their polar head group pointing to the bulk solution.30 Thereby the free fatty acid gain greater activity with more exposed carboxyl under such circumstance, it is easier for them to combine with metal ions by saponification process. Consequently, the approached free LA at the cathode surface is codeposited in the form of laurate. In summary, the refined LA can be uniformly co-deposited and attributes to the successful superhydrophobicity. It seems this ultrasonic-irradiated manner helps achieve an optimized organic-inorganic composite exhibiting high structural strength in our experiment. The brief illustration of the deposition mechanism is disclosed in Scheme 1. On other hands, the SEM images and XRD spectrum show that the coated surface is prominently characterized by a nanocrystalline growth mode, which reveals an effect of ultrasound leading to the generation of nanomaterials.33-35 Through our investigation, more


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advantages as anti-corrosion and wear-resistant ability of this nanocrystalline coating were found, which will be discussed in the next section.

Scheme 1. The mechanism of the lauric acid co-deposition. 3.5. Performance of the Coating. 3.5.1. Anti-wear Property. The mechanical stability was examined by linear abrasion test on the coated SS substrates. To search for detailed information, electrolyte at a series of nickel sulfate concentrations (from 0.038 to 0.27 M) were prepared while all at the LA concentration of 2.5 mM. The fabricated films were tested by applying a pressure of 1.3 kPa upon the substrate with 1 N weight, followed by dragging the substrate to move in one direction on a 1000 grit sandpaper (shown in Figure 8a). WCA data was recorded by each 1 m till a total abrasion length of 4 m. As results demonstrates in Figure 8c, the 0.19 M and 0.27 M results present superhydrophobicity even after a 4 m abrasion length, which performs a 10 times improvement from a former report23 that was tested under the same friction load. Besides, quite opposite variation trends of WCA for the low Ni2+ concentration products (as the 0.038 and 0.11 M results) and high Ni2+ concentration products (the 0.19 and 0.27 M results) are observed during the abrasion test.


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Figure 8. (a) The illustration of the linear abrasion test and (b) a photo showing the waterresistant property after an abrasion test. (c) The WCA variation of the coating that fabricated under different NiSO4 concentration. The SH behavior can be analyzed with the aid of Cassie’s equation for a solid-liquid interface: cos θr = f1 cos θ − f2

(5)

Where θr is the WCA on the porous SH surface, θ is the WCA on a corresponding smooth coated surface (θ = 90.0° for a smooth Ni-Cu coating surface that was modified afterward by LA, exhibits in Figure S3). f1 is the liquid/solid contact area divided by the projected area; and f2 is the liquid/vapor contact area divided by the projected area (f1 + f2 = 1). Through calculation based on this equation, the f1 values for the two different Ni2+ concentration products before and after the abrasion are summarized in Table 3: Table 3. Liquid/solid Contact Area Before and After the Abrasion. 0.038 M product WCA of surface /° before

smooth

WCA /°

0.27 M product 90.0

144.1


146.8

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abrasion

f1

0.11

0.096

after abrasion

WCA /°

132.6

150.3

f1

0.19

0.077

Followed by investigating the surface morphologies, the SEM images of the 0.038 and 0.27 M products reveal significant differences before and after abrasion. It discovers on both of the intrinsic surfaces the aforementioned micron scale structural units, but they seemed to be more isolated from each other on the surface fabricated from a low Ni2+ concentration electrolyte while more densely distributed on that from the opposite high Ni2+ concentration electrolyte (see Figure 9a and 9b). Figure 9c indicates that the surface with sparse microstructures cannot withstand the friction load and the rough morphology has been almost destroyed within the friction track. The disappearance of micro/nano-scaled rough morphology can explain for the higher f1 after abrasion and thus presented a lower WCA (depicted in Figure 9e). However, much different morphology change is detected on the surface that with the densely distributed microunits (see Figure 9d). Though suffering some damages, the resulted fragments shows a rearrangement on the original surface instead of being stripped away, and a new type of hierachical morphology is created. It seems this sort of structure may present a preferably lower f1 value and resulted in unconventional WCA enhancement (depicted in Figure 9f). These phenomenon matches the results of former studies,20,36 where the SH surface exhibited improved mechanical durability by exposing less isolated or sharp-terminal structures, since the decrease of contact area will result in undesirable higher contact pressure upon load and thus the surface suffered more serious damage. In conclusion, the mechanical strength of this coating can be controlled in the microscopic level by simply adjusting the metal ion concentration of the electrolyte.


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Figure 9. The as-deposited surface morphology of the film fabricated at (a) 0.038 M and (b) 0.27 M NiSO4. The abrasion marks and the illustration of solid-liquid contacting of the coating at (c),(e) 0.038 M and (d),(f) 0.27 M NiSO4. 3.5.2. Anti-corrosion Property. A test of extreme condition was carried out by directly immersing the deposited SS plate in highly concentrated hydrochloric acid (12 M). It has been found from Figure 10a that only small amount of hydrogen bubble generated on the coated side, while the bare metal side was under drastic dissolution. The picture in Figure 10b discovers negligible distraction of the coating and a WCA of 141.5° maintained even after 30 min immersion.


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Figure 10. (a) The comparison of the bare and coated surface after immersed in 12 M HCl for different time; (b) the WCA of the bare and the coated surface after 30 min immersion in acid. (c) The Tafel plots for difference surfaces. Further more, standard corrosion test had been done on an electrochemical workstation (LK 2010) in a 3.5 wt.% NaCl solution at room temperature. In general, the anti-corrosion ability of SH surfaces is ascribed to the storage of air layer (at the namely Cassie-Baxter state37). But when it turned to a wetting state (at the Wenzel state38), the highly porous nature of the film may create more passways for the entry of corrosive medium and cause higher corrosion rate. Figure 10c gives the electrochemical polarization curves for the brass SS, copper, aluminum substrate as well as the coating surface at Wenzel and Cassie-Baxter state. Despite the corrosion potential (Ecorr) of the Cu sheet reached a relative high value of -0.112 V, whether the coating under the


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air layer-covered or wetting condition demonstrates an efficient anti-corrosion property, each enjoying an obviously more positive Ecorr of -0.171 and -0.427 V than the bare SS and aluminum surfaces, and a smaller corrosion current density (icorr) of 0.366 and 0.201 mA/cm2 than all the three bare metal surfaces. This confirms that the coating itself can offer a secondary protection even in case the superhydrophobicity was lost, helping it being more competent to the practical issues. 3.5.3. Extensibility and Bonding Strength Tests. The extensibility test was carried out on the aluminum foil (0.1 mm in the thickness) with the superhydrophobic film. Shown in Figure 11a is the as-prepared film undergoing an over 160° bending successively in two directions. Only one unconspicuous and discontinuous crack appeared. It is convinced that an 160° bending will incur huge curvature and generate great localized stress on the coating, hence proves that the metallic coating can withstand the stretching or extruding force under very harsh condition. To investigate the adhesion property, we conducted the cross cut tape test according to the ASTM standard D3359-02 afterward (as in Figure 11b). With a coating area of 3 × 1.8 cm, the prepared copper plate appeared no squares peeled off and there were few notable traces on the adhesive tapes after pull and removal of the tapes.


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Figure 11. The testing of extensibility and bonding strength.

4. CONCLUSIONS

In this work, we have introduced a water-based electrodeposition technique toward multifunctionalized superhydrophobic products by one-step operation, which gets rid of the drawbacks among the common one-step approach that relying on the pollutive organic solvents. The electrodeposition duration can be as short as below 5 min on many sorts of substrates. Besides, the superhydrophobic coating can be satisfactorily prepared on a sufficient large surface. The fabricated SH coating exhibited excellent mechanical durability, anti-corrosion ability and extensibility. It is convinced that this finding possesses huge potential for the quantity production of oil-water separation, self-cleaning and anti-corrosion materials.

ASSOCIATED CONTENT


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Supporting Information The coated carbon cloth exhibited high resistance to coffee (Figure S1), the fabrication of SH coating on the inner wall of a large U-shaped workpiece (Figure S2), and the water drop images on a bare SS surface and a smooth Ni-Cu coating surface (Figure S3). AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (H.Y.Wang). Tel.: 0086-4596503083. Notes The author declare no competing financial interest. ACKNOWLEDGEMENT The research is financially supported by the National Young Top Talents Plan of China (2013042), National Science Foundation of China (21676052, 21606042), the Science Foundation for Distinguished Young Scholars of Heilongjiang Province (JC201403). REFERENCES (1) Passoni, L.; Bonvini, G.; Luzio, A.; Facibeni, A.; Bottani, C. E.; Fonzo, D. F. Multiscale Effect of Hierarchical Self-Assembled Nanostructures on Superhydrophobic Surface. Langmuir 2014, 30, 13581-13587. (2) Wang, Z.; Li, Q.; She, Z.; Chen, F.; Li, L. Low-Cost and Large-scale Fabrication Method for an Environmentally-Friendly Superhydrophobic Coating on Magnesium Alloy. J. Mater. Chem. 2012, 22, 4097-4105. (3) Ramakrishna, S.; Santhosh Kumar, K. S.; Mathew, D.; Reghunadhan Nair, C. P. A Robust, Melting Class Bulk Superhydrophobic Material with Heat-Healing and Self-Cleaning Properties.


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For Table of Contents Only Toward Easily Enlarged Superhydrophobic Materials with Stain-resistant,

Oil-Water

Separation

and

Anti-corrosion

Function by a Water-based One-step Electrodeposition Method Huaiyuan Wang∗, Ziyi Hu, Yixing Zhu, Shuhui Yang, Kai Jin, Yanji Zhu College of Chemistry and Chemical Engineering, Northeast Petroleum University, Daqing, China

∗

Corresponding author. Tel.: 0086-4596503083; Fax: 0086-4596503083.

E-mail address: [email protected] (H.Y.Wang)


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For Table of Contents 84x47mm (300 x 300 DPI)


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Toward Easily Enlarged Superhydrophobic Materials with Stain

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