Rough Structure of Electrodeposition as a Template for an Ultrarobust

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Rough Structure of Electrodeposition as a Template for an Ultrarobust Self-Cleaning Surface Yongquan Qing,*,† Chuanbo Hu,‡ Chuanning Yang,† Kai An,† Fawei Tang,§ Junyang Tan,† and Changsheng Liu*,† †

Key Laboratory for Anisotropy and Texture of Materials, Ministry of Education, Northeastern University, Shenyang 110819, China School of Metallurgy, Northeastern University, Shenyang 110819, China § College of Materials Science and Engineering, Key Laboratory of Advanced Functional Materials, Education Ministry of China, Beijing University of Technology, Beijing 100124, China ACS Appl. Mater. Interfaces 2017.9:16571-16580. Downloaded from pubs.acs.org by UNIV OF SUNDERLAND on 10/01/18. For personal use only.

‡

S Supporting Information *

ABSTRACT: Superhydrophobic surfaces with self-cleaning properties have been developed based on roughness on the micro- and nanometer scales and low-energy surfaces. However, such surfaces are fragile and stop functioning when exposed to oil. Addressing these challenges, here we show an ultrarobust self-cleaning surface fabricated by a process of metal electrodeposition of a rough structure that is subsequently coated with fluorinated metal-oxide nanoparticles. Scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction were employed to characterize the surfaces. The microand nanoscale roughness jointly with the low surface energy imparted by the fluorinated nanoparticles yielded surfaces with water contact angle of 164.1° and a sliding angle of 3.2°. Most interestingly, the surface exhibits fascinating mechanical stability after finger-wipe, knife-scratch, sand abrasion, and sandpaper abrasion tests. It is found that the surface with superamphiphobic properties has excellent repellency toward common corrosive liquids and low-surface-energy substances. Amazingly, the surface exhibited excellent self-cleaning ability and remained intact even after its top layer was exposed to 50 abrasion cycles with sandpaper and oil contamination. It is believed that this simple, unique, and practical method can provide new approaches for effectively solving the stability issue of superhydrophobic surfaces and could extend to a variety of metallic materials. KEYWORDS: self-cleaning surface, superamphiphobic, electrodeposition, micro- and nanostructures, ultrarobust surface

1. INTRODUCTION Bioinspired superhydrophobic surfaces with self-cleaning function, characterized by water contact angles (CA) greater than 150° and sliding angles (SA) below 10°, have attracted enormous attention in both industrial and academic fields.1−4 Self-cleaning surfaces rely upon water droplets forming near spherical shapes, and because of repulsion, these droplets easily roll on the surface, collecting dirt as they do so.5−7 The combination of roughness on the micro- and nanoscales with low-energy surfaces led to the development of artificial selfcleaning surfaces through various methods, including top-down (e.g., etching,8 lithography9) and bottom-up types (e.g., sol− gel,10 layer-by-layer deposition11). The main disadvantages of these artificial surfaces include poor mechanical stability, easy abrasion, and contamination by oil. To date, several investigations have attempted to solve these problems by establishment of covalent bonding or cross-linking a coating layer between the substrate and the coating.12−15 With these attempts, the stability of the surface was improved to a certain extent; however, achieving excellent surface superhydropho© 2017 American Chemical Society

bicity while retaining robust stability is still difficult; thus, this problem has not been fundamentally solved. To solve these challenges, some mechanically stable superhydrophobic surfaces have been reported by relying on an intrinsic stable media (i.e., metal meshes, polymer, or fabric).16,17 Deng et al.18 reported candle soot as a template for a robust superamphiphobic coating. A breakthrough was achieved by Lu and co-workers, who fabricated a robust selfcleaning surface from both soft and hard materials by combining paint and adhesives.6 Zhou et al.1 developed a cross-linked elastomeric thin coating with a nanocomposite rough structure and low free-energy surface, which endowed fabrics with highly durable superhydrophobicity. Wong et al.19 prepared a large-scale ultradurable and transparent superhydrophobic surface by rapid template-free nano- and microtexturing of tough polymers. Wang and Lin20 reported a robust Received: December 9, 2016 Accepted: April 25, 2017 Published: April 25, 2017 16571

DOI: 10.1021/acsami.6b15745 ACS Appl. Mater. Interfaces 2017, 9, 16571−16580

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ACS Applied Materials & Interfaces

Figure 1. Schematic illustration of the superhydrophobic FAS-TiO2/Zn surface formation process via a two-step method.

hydrophobic nanoporous tungsten oxide coating on various grades of steel via electrodeposition. The mechanical durability of the coating was significantly improved because of chemical bonding with the substrates. Although the as-prepared electrodeposited surface stability was very good, it was easy to lose superhydrophobicity if some external force was applied (e.g., a knife-scratch or abrasion damages). Highly inspired by this, we hypothesized that if the modified nanoparticles could be transferred to the rough structure based on electrodeposition, a robust superhydrophobic surface could be fabricated for practical applications. To this end, herein we report a facile method for fabricating a robust superamphiphobic and self-cleaning surface by a process that involves electrodeposition technology as a tool to produce a stable rough surface, fluoro-silanization of TiO2 nanoparticles, and coating of these onto the rough electroplated surface creating re-entrant structures. By combining the rough structure and modified-nanoparticles, we fabricated a robust surface durable against applied external forces (i.e., finger-wipe, knife-scratch, sand abrasion, and sandpaper abrasion damages) that retained its self-cleaning capability. Moreover, compared to other techniques for fabricating self-cleaning surfaces, this technique has the advantages of being simple, cost-effective, and unique and could be applied to any metal surface.

superoleophilic and superhydrophobic carbon nanotube/poly(dimethylsiloxane)-coated polyurethane sponge for use in oil spill cleanups. These studies make use of an intermediate template to improve the stability of the superhydrophobic surfaces; however, these surfaces are easily damaged under the action of large external forces, mainly because of the lack of hardness in their structures. Copper is an important engineering material, owing to its good ductility, excellent thermal conductivity, and relatively noble properties. It is widely used in many modern industrial areas, especially decorative devices, conductors, lead frames, and aerospace applications. Thus, it is very desirable to fabricate a superhydrophobic copper surface with superior waterrepellence ability. A variety of methods have been developed to prepare superhydrophobic surfaces based on copper substrates,21−24 but reports about mechanically stable selfcleaning copper surfaces are still scarce.25 Titanium dioxide (TiO2) nanostructures have become the focus of enormous interest in biomaterials because of their antibacterial properties, efficiency as photocatalyst, biocompatibility, and good chemical stability.26 Electrodeposition, as a classic technique for fabrication of metal matrix surface which exhibits extraordinary durablility, has the advantages of ease of control, low cost, and high effectiveness. Currently, several studies investigating the preparation of superhydrophobic surfaces via electrodeposition have been reported.25,27−29 In all these studies, a rough structure of a transition-metal layer is first constructed, which is followed by modification with the low-surface-energy material (such as stearic acid, myristic acid, fluoroalkylsilane). Su and Yao25 created a superhydrophobic surface on copper substrate through electrodeposition in traditional Watts bath and heattreatment in the presence of (heptadecafluoro-1,1,2,2tetradecyl)triethoxysilane. Tesler et al.30 fabricated a super-

2. EXPERIMENTAL SECTION 2.1. Materials. Copper plates with dimensions 100 × 60 × 1 mm3 were selected as the substrate. Zinc sulfate hetahydrate (ZnSO4·7H2O) was purchased from Tianjin Kemiou Chemical Reagent Co., Ltd. Dongguan City JiShun Import and Export Co., Ltd. supplied nanoTiO2 (rutile) with an average size of 25 nm. 1,1,2,2-Tetrahydroperfluorodecyltrimethoxysilane (FAS) was provided by Shanghai Aladdin-Reagent Co., Ltd. 2.2. Pretreatment of Copper Substrate. The copper substrate was mechanically polished down to 1200−1500 grit size using abrasive 16572


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Figure 2. Tilt-view SEM images of (a and b) deposited Zn surface and (d and e) FAS-TiO2/Zn surface at different magnifications. (The inset corresponds to the cross-section.) LSCM topographical images of (c) deposited-Zn surface and (f) FAS-TiO2/Zn surface. silicon carbide (SiC) paper, followed by ultrasonic cleaning in acetone for 10 min and rinsing with deionized water. The substrate was processed almost immediately by electrolytic degreasing and electropolished at 1.5 A·dm−2 in a solution containing sodium carbonate (Na2CO3, 0.57 M), potassium hydroxide (KOH, 0.018 M), and sodium dodecyl sulfate (0.028 M) for 2 min. Furthermore, it was dipped in an activation solution containing hydrochloric acid (HCl, 10 wt %) for 30 s at room temperature to remove the oxide film. It was then quickly placed in the electrolytic bath after rinsing with deionized water. 2.3. Electrodeposition of Zinc. Zinc was electrodeposited based on the method described in our previous study.31 Briefly, the Ti-IrO2 and Cu substrate were used as anode and cathode in an electrolyte solution, respectively. A distance of 2 cm separated the anode and cathode plates. The optimized bath contained ZnSO4·7H2O (0.77 M), and the pH was adjusted to 2.0 using sulfuric acid solution (H2SO4, 50 g·L−1). The electrodeposition process was performed by a direct current (DC) power with current densities of 11−23 A·dm−2 at 40 °C. After being subjected to electrolysis for 25 min, the cathode was rinsed several times with distilled water and dried, forming a rough depositedZn surface. 2.4. Preparation of Self-Cleaning FAS-TiO2/Zn Surface. We modified the surface of TiO2 particles by a hydrothermal reaction technique.32 In detail, FAS (1 g) was placed into absolute ethanol (15 mL) which was then well mixed. Then, TiO2 particles (3 g) were added to this mixed solution. The mixture was magnetically stirred at 40 °C for 50 min to form a paintlike coating solution. Subsequently, the deposited-Zn sample was immersed in the coating solution at 80 °C for 20 min, and then the sample was left in air for 10 min and placed in an oven at 120 °C for 30 min. Finally, excess residue on the sample surface was removed by ultrasonic oscillation for 10 min, leaving behind the self-cleaning FAS-TiO2/Zn surface. 2.5. Characterization. The surface morphology of the as-prepared samples was examined by scanning electron microscopy (SEM, FEI Nova NanoSEM 430, 10 kV), and energy dispersive X-ray spectroscopy (EDS) data were acquired using the same instrument. Fouriertransform infrared spectrophotometry (ATR-FTIR, PerkinElmer, United States) and X-ray photoelectron spectroscopy (XPS, KAlpha, United States) were used to determine the chemical composition of the surfaces. The CA and SA were measured with ∼3 μL water droplets at room temperature using a JCY-2 instrument

(Fangrui, China). The surface roughness (Ra) of the samples, with length of 1280 μm, was measured using an OLS3100 laser confocal scanning microscope (LSCM, Japan). X-ray diffraction (XRD, Bruker D8, Germany) was used to elucidate the crystal structure of the samples.

3. RESULTS AND DISCUSSION 3.1. Surface Morphology and Chemical Composition. It is well-known that a superhydrophobic surface can be fabricated based on the combined effects of both low-surfaceenergy materials and micro- and nanocomposite surface structure.33,34 Figure 1 presents the formation process of a superhydrophobic FAS-TiO2/Zn surface. TiO2 nanoparticles are hydrophilic because of the large number of hydroxyl groups existing on its surface, whose free energy can be effectively reduced by self-assembling FAS, because of its high content of −CF2− and −CF3 groups with low surface energy of 18 and 6.7 m·Jm2−,35 respectively. First, the silicon ethoxide groups (Si− OCH2CH3) in FAS are converted to silanol groups (Si−OH) after hydrolysis, which act as reactive groups at the end of the molecule, and then react with the −OH groups of the TiO2 surface to form a self-assembled coating solution. This paintlike coating solution was directly applied onto the deposited-Zn surface using dip-coating. Then the sample was left in air to remove the solvent, followed by curing at 120 °C for 30 min. Thus, an ultrarobust self-cleaning surface was successfully fabricated. Moreover, a water drop placed on top of the FASTiO2/Zn surface formed a static CA of 164.1° and a SA of 3.2°, owing to the significantly reduced adhesion of water to surface. The difficulty for water droplets to deposit on the surface allows them to immediately roll off (Movie S1), indicating that the surface is expected to exhibit a water-repellent effect. On the basis of the model described above, Figure 2a−d shows the tilt-view SEM images with different magnifications of deposited-Zn surfaces and FAS-TiO2/Zn surfaces. Figure 2a,b exhibits that the morphology of the deposited-Zn surface is rather rough and composed of a large number of protrusive 16573


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Figure 3. Tilt-view SEM images of FAS-TiO2/Zn surface: (a) low-magnification image, (b) cross-sectional view of panel a, and (c) magnified image of panel b. Corresponding EDS chemical composition of line-scan (d, e, and f) and area-scan (g, h, and i) signal intensity mapping showing the spatial distribution of the elements Zn, Ti, and O, respectively.

microstructures, with sizes in the range of 10−25 μm, forming microscale rough structures. There are numerous gaps, with an average size of 5−10 μm, between hill-like protrusive structures. The deposited-Zn surface (CA = ∼10.2°) could not support a water droplet in contact with it in the Wenzel’s state,36 indicating that no air pockets were formed so that the surface was completely wetted. Figure 2d,e clearly shows that numerous irregular nanoparticles (with size ranging from dozens to hundreds of nanometers) are attached to the hilllike rough structure surface, forming submicroscale rough structures. Furthermore, nano FAS-TiO2 particles were deposited on microscale rough structure surface, and the covalent bonding occurred between FAS-TiO2 phase and the Zn plated layer (physical bonding or chemical changes), indicating the occurrence of better adhesion between layers of particles and Zn (Figure 3). According to the Cassie−Baxter model,37 the phenomena of superhydrophobicity is explained in terms of trapped air films in the holes and grooves present on submicroscale rough surface structures. These air films can effectively prevent the surface from being wetted by water droplets, leading to larger CA and smaller SA. Further evidence of the Ra is given by LSCM images of the deposited-Zn surface and FAS-TiO2/Zn surface (Figure 2c,f). The Ra values of deposited-Zn surface and FAS-TiO2/Zn surface are 31.3 and 9.1 μm, respectively. Rough surface structure is indispensable for the surface to present superhydrophobicity. The air gets easily trapped in the apertures because the FAS-TiO2/Zn surface has a sufficiently rough structure. The LSCM results

further confirmed that the submicroscale rough structures were formed on the composite surface. In general, the pH and concentration of precursor solution, current density, time, and temperature of electrodepositon influence the microtopography of deposited surface.28,38,39 This study, based on previous reports,31,40 mainly considered the effect of current density on wettability to evaluate the real contribution of Ra toward superhydrophobicity. Figure S1 demonstrates that the superhydrophobicity of the FAS-TiO2/ Zn surface is obviously enhanced with the increase in the current density: the CA increases to 164.1° from 154.3°, and the value of Ra increases to 9.1 μm from 5.3 μm. The superhydrophobicity of the FAS-TiO2/Zn surface was the best when current density was 17 A·dm−2. However, the superhydrophobicity of the FAS-TiO2/Zn surface significantly decreased when the current density exceeded 17 A·dm−2: the CA was decreased to 150.1° from 164.1°, and the Ra was increased to 17.9° from 9.1° with the increase in the current density. This indicates that the surface wettability and Ra can be effectively controlled by regulating the current density. Figure 4 displays the ATR-FTIR and EDS spectra of the deposited-Zn and FAS-TiO2/Zn surfaces. Compared to the spectrum of the initial deposited-Zn surface (Figure 4a), many absorption peaks are detected corresponding to the FAS-TiO2/ Zn surface (Figure 4b). The peak at 1064 cm−1 is the characteristic absorption peak of Si−O−Si; peaks located at ∼1317, 1243, 1207, 1143, and 1115 cm−1 are assigned to the C−F stretching vibration of the −CF3 and −CF2− groups in the fluorinated alkyl chains,41 indicating the successful attach16574


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Figure 4. Chemical composition analysis of the surface: ATR-FTIR spectra of (a) deposited-Zn surface and (b) FAS-TiO2/Zn surface; EDS spectra of (c) deposited-Zn surface and (d) FAS-TiO2/Zn surface.

ment of the FAS-TiO2 film, thus covering the deposited-Zn surface. Figure 4c,d shows the EDS spectra of electrodeposited Zn and FAS-TiO2/Zn surfaces, which corresponds to the concentrations of elements present on the surfaces. The results indicate that the deposited-Zn surface contains only the element Zn (Figure 4c), while the FAS-TiO2/Zn surface mainly consists of elemental C, O, F, Si, Ti, and Zn (Figure 4d), further confirming the attachment of the FAS-TiO2 film, covering the Zn surface. XPS was used to further determine the chemical composition of the FAS-TiO2/Zn surface. In a wide survey, strong signals of C 1s, F 1s, Ti 2p, O 1s, and Zn 2p and a weak signal of Si 2p were detected on the surface (Figure S2). High-resolution spectra for C 1s, F 1s, Ti 2p, O 1s, and Zn 2p were deeply analyzed, as shown in Figure 5. The C 1s peak can be deconvoluted into six peaks located at 294.4, 292.0, 289.7, 287.7, 285.5, and 282.6 eV, which are ascribed to the carbon atoms of −CF3, −CF2−, −CF2−CF3, −CH2−CF2−, −CH2−, and −CH2−Si groups, respectively.42 In addition, the only peak component appearing at the binding energy of ∼689.4 eV in the F 1s core-level signal is associated with the C−F species (Figure 5a).43 This indicates that the FAS monolayer of low surface energy was immobilized on the TiO2 surface. The Ti 2p high-resolution spectrum is shown in Figure 5b and can be deconvoluted into peaks at 465.3 eV (Ti 2p 1/2) and 459.5 eV (Ti 2p 3/2) referring to TiO2. The doublet peak energy separation is 5.8 eV, consistent with that reported in a previous study.44 In the O 1s spectra (Figure 5c), new peaks that arise at 533.3, 532.3, and 530.8 eV corresponding to Si−O, ZnO (OH), and Ti−O are detected, and a strong Zn 2p signal can be deconvoluted into peaks at 1046.0 eV (Zn 2p 1/2) and 1022.8 eV (Zn 2p 3/2), indicating the presence of a Zn−O bond.45

Figure 5d displays XRD patterns of rutile TiO2, FAS-TiO2, deposited-Zn, and FAS-TiO2/Zn. The characteristic diffraction peak of TiO2 does not exhibit any change after modification with FAS. The main peaks that appeared at 2θ of 25.3°, 37.7°, 47.9°, 54.7°, and 62.7° show the expected pattern for rutile TiO2 (JCPDS 65-5714)46 and that the FAS molecules are amorphous (Figure 5d(i)). The six characteristic diffraction peaks of deposited Zn are found at 36.5°, 39.2°, 43.7°, 54.8°, 70.6°, and 82.4° corresponding to the (002), (100), (101), (102), (110), and (112) planes (JCPDS 65-5973), indicating a hexagonal crystal structure (Figure 5d(iii)).47 The sharp and strong reflection peaks indicate that the FAS-TiO2/Zn composite material is well-crystallized (Figure 5d(iv)). 3.2. Mechanical Stability. Superhydrophobic surfaces usually present a rough structure in the micro- or nanoscale and have poor mechanical properties, limiting their use in practical applications.25,39,48 We developed a method to fabricate a self-cleaning surface by using a nanoparticle-filled stable rough structure of electrodeposition for overcoming the weak robustness of superhydrophobic surface. Figure S3 exhibits the “substrate + rough structure + modified-nanoparticle” sample preparation methods (Figure S3a). To investigate the mechanical stability of our coating, we performed several tests including finger-wipe (Figure S3b), knife-scratch (Figure S3c), sand abrasion (Figure S3d), and sandpaper abrasion (Figure S3e). Figure S4 and Movie S2 show the comparison of the finger-wipe and knife-scratch tests on the FAS-TiO2-treated and “rough structure + FAS-TiO2”-treated Cu substrates, respectively. After the finger-wipe and knifescratch tests, the FAS-TiO2 directly coated on the Cu substrate was removed and exhibited a loss of superhydrophobicity. On the other hand, the FAS-TiO2/Zn surface remained on the Cu substrate and thus maintained excellent superhydrophobic 16575


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Figure 5. XPS spectra of the FAS-TiO2/Zn surface: (a) C 1s, (b) Ti 2p, and (c) O 1s high-resolution spectra. The insets correspond to the highresolution F 1s spectra (a) and Zn 2p spectra (c). (d) XRD patterns of (i) rutile TiO2, (ii) FAS-TiO2, (iii) deposited-Zn, and (iv) FAS-TiO2/Zn surfaces.

properties. Sand grains (200−400 μm diameter) impinged upon the FAS-TiO2/Zn surface from a height of 70 to 100 cm, corresponding to an impinging energy of 4.6 × 10−8 to 5.3 × 10−7 J per grain, showed only slight changes in CA and SA of the surface (Figure S3d). Mechanical abrasion resistance test is an effective method to evaluate the stability of superhydrophobic surfaces.6,25,49 The superhydrophobic FAS-TiO2/Zn surface, weighing 100 g, was placed facedown to 400 grit SiC sandpaper. It was first moved for 10 cm along the ruler at a constant speed (Figure 6a), and then the sample face to the sandpaper was rotated by 90° and moved for 10 cm along the ruler (Figure 6b). This process is defined as one abrasion cycle (Movie S3). Surprisingly, the surface still showed good superhydrophobicity after 50 abrasion cycles, and the CAs were between 164.1° and 156.2° (Figure 6c). Furthermore, the surface morphology after abrasion test was studied by SEM. Figure S5 shows the surface morphology, exhibiting a few of abrasion scratches, and the FAS-TiO2/Zn surface provides concave and convex grooves, which can effectively resist the mechanical abrasion. Figure 6d shows the tiny variation of surface hydrophobicity with the increase in applied pressure; the surface still exhibits superhydrophobicity

with a CA of 157.8° and a SA of 8.2° after abrasion for 20 cm at 12 kPa. These results indicate the excellent mechanical abrasion resistance of the superhydrophobic surface. 3.3. Self-Cleaning Property. It is important for superhydrophobic surfaces to have self-cleaning properties in practical applications. The self-cleaning tests are shown in Figure S6 (the experimental schemes) and Figures S7 and 7 (the experimental results). Figure S7a,b demonstrates that deposited-Zn and FAS-TiO2/Zn surfaces were placed in red ink dyed water and subsequently removed. The red liquid wetted the deposited-Zn surface while the FAS-TiO2/Zn surface remained in its initial state with no trace of contamination. Figure S7c,d shows the process of the self-cleaning effect. Dirt (graphite and dust) was placed on the sample surface, and then it was cleaned by fast running water droplets. The deposited-Zn surface was wet and remained contaminated by the dirt; however, the FAS-TiO2/Zn surface very quickly became clean and stayed dry throughout. These tests indicate that the FASTiO2/Zn surface possesses excellent antifouling ability. To date, much of the investigations in the literature conclude that superhydrophobic surfaces tend to be contaminated easily by oil and thus lose their self-cleaning properties. This is 16576


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Figure 6. (a and b) Schematic illustration of sandpaper abrasion test (one cycle); (c) CA and SA as a function of mechanical abrasion cycle number for the superhydrophobic FAS-TiO2/Zn surface. The inset is water droplet traveling test after 50th abrasion cycle. (d) CA and SA of the superhydrophobic FAS-TiO2/Zn surface with increasing applied pressure after abrasion for 20 cm.

Figure 7. Self-cleaning effect of the FAS-TiO2/Zn surface (superamphiphobic surface) after 50th abrasion cycle with sandpaper. (a) Different types of liquid droplets with spherical shape on superamphiphobic surface: red-colored H2O droplet, black-colored HCl droplet, blue-colored NaOH droplet, and oil droplet. (b) Red-colored H2O droplets sitting on the FAS-TiO2/Zn surface under oil (lower image) and on rough electrodeposited Zn surface (upper image). (c−f) Self-cleaning process of the superamphiphobic surface after being contaminated by oil.

attributed to the fact that the surface tension of oil is lower than that of water, so the oil penetrates the surface, thereby

removing the trapped air layer. Although many groups have reported that fabrication of superamphiphobic surfaces (that 16577


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This simple, cost-effective, and unique technique can provide new ideas for designing robust superhydrophobic materials and can be further extended to a variety of metal substrates.

repel both nonpolar liquids and water) can effectively prevent the contamination of oil on the surface,18,50,51 these surfaces lose their self-cleaning properties permanently when an external force is applied (e.g., finger-wipe, sandpaper abrasion etc.). We developed an FAS-TiO2/Zn surface with superamphiphobic properties because its outermost surface contains −CF2− and −CF3 groups. Figure 7 shows the self-cleaning effect of the superamphiphobic surface after the 50th abrasion cycle with sandpaper. Figure 7a reveals the high CA exhibited by the surface for a wide variety of liquid drops, (e.g., HCl, NaOH, and oil), demonstrating excellent repellency toward common corrosive liquids and low-surface-energy substances. Figure 7b illustrates the surface after immersion in oil. Clearly, water droplets sit on the superamphiphobic surface. This is due to the support provided by both the surface structures and oil (lower image of Figure 7b); moreover, water droplets spread and wet the hydrophilic deposited-Zn surface (upper image of Figure 7b). Figure 7c−f demonstrates the immersion of superamphiphobic surface in oil for 5 min after being contaminated and subsequently cleaned. Dirt was then put onto the surface, and it was removed by passing water droplets (Movie S4). Therefore, it can be concluded that the superamphiphobic surface can protect the substrate from abrasion and oil contamination in practical applications. Thus, herein we described an ingenious strategy overcoming many challenges in the realization of stable self-cleaning surfaces on copper substrate, which can be applied under harsh mechanical abrasion and oily environments. A combination of SEM, ATR-FTIR, XPS, and XRD characterization showed that the rough surface with submicroscale structures was created and that the low-surface-energy fluorinated components were successfully prepared on the deposited-Zn surface on copper substrate through this new method. The mechanical stability of superhydrophobic FAS-TiO2/Zn surface was found to be significantly improved because of the structure and bonding strength of the interface between deposited-Zn and the FAS-TiO2 coating. It is believed that the unique idea of “substrate + rough structure + modified-nanoparticle” can be simple, cost-effective, and widely used in a variety of metal substrates (such as steel, magnesium alloy, and aluminum alloy).

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.6b15745. Addtional experimental results (Figures S1−S7) and descriptions of supporting videos (PDF) Movie S1: FAS-TiO2/Zn surface (AVI) Movie S2: Knife-scratch tests on the “rough structure + FAS-TiO2”-treated Cu substrates (AVI) Movie S3: Sandpaper abrasion test (AVI) Movie S4: Self-cleaning tests of the superamphiphobic surface (AVI)

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AUTHOR INFORMATION

Corresponding Authors

*C.L.: e-mail, [email protected], [email protected]; tel, +86 02483687365; fax, +86 02423906313. *Y.Q.: e-mail, [email protected]; tel, +86 02483687365; fax, +86 02423906313. ORCID

Yongquan Qing: 0000-0002-9431-2579 Changsheng Liu: 0000-0002-2087-427X Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Frontier and Key Technical Innovation of Guangdong Province (2015B010122001) and the Joint Founds of NSFC-Liaoning (U1508213).

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REFERENCES

(1) Zhou, H.; Wang, H.; Niu, H.; Gestos, A.; Wang, X.; Lin, T. Fluoroalkyl Silane Modified Silicone Rubber/Nanoparticle Composite: a Super durable, Robust Superhydrophobic Fabric Coating. Adv. Mater. 2012, 24, 2409−2412. (2) Timonen, J. V.; Latikka, M.; Leibler, L.; Ras, R. H.; Ikkala, O. Switchable Static and Dynamic Self-assembly of Magnetic Droplets on Superhydrophobic Surfaces. Science 2013, 341, 253−257. (3) Liu, T.; Kim, C. J. Turning a Surface Superrepellent Even to Completely Wetting Liquids. Science 2014, 346, 1096−1100. (4) Liu, K.; Jiang, L. Bio-Inspired Self-Cleaning Surfaces. Annu. Rev. Mater. Res. 2012, 42, 231−263. (5) Parkin, I. P.; Palgrave, R. G. Self-Cleaning Coatings. J. Mater. Chem. 2005, 15, 1689−1695. (6) Lu, Y.; Sathasivam, S.; Song, J.; Crick, C. R.; Carmalt, C. J.; Parkin, I. P. Robust Self-Cleaning Surfaces that Function When Exposed to Either Air or Oil. Science 2015, 347, 1132−1135. (7) Yang, Q.; Luo, Z.; Jiang, F.; Luo, Y.; Tan, S.; Lu, Z.; Zhang, Z. Z.; Liu, W. Air Cushion Convection Inhibiting Icing of Self-Cleaning Surfaces. ACS Appl. Mater. Interfaces 2016, 8, 29169−29178. (8) Xiu, Y.; Zhu, L.; Hess, D. W.; Wong, C. P. Hierarchical Silicon Etched Structures for Controlled Hydrophobicity/Superhydrophobicity. Nano Lett. 2007, 7, 3388−3393. (9) Gao, X.; Yan, X.; Yao, X.; Xu, L.; Zhang, K.; Zhang, J.; Yang, B.; Jiang, L. The Dry-Style Antifogging Properties of Mosquito Compound Eyes and Artificial Analogues Prepared by Soft Lithography. Adv. Mater. 2007, 19, 2213−2217. (10) Manca, M.; Cannavale, A.; De Marco, L.; Arico, A. S.; Cingolani, R.; Gigli, G. Durable Superhydrophobic and Antireflective Surfaces by

4. CONCLUSION In summary, we presented an ingenious method of fabricating an ultrarobust self-cleaning surface with submicroscale rough structures on copper substrate using a nanoparticle-filled stable rough structure by electrodeposition. The resultant superhydrophobic surface, with high CA (164.1°) and small SA (3.2°), was acquired through the attachment of FAS-TiO2 film, covering the deposited-Zn surface that created the covalent bonding with better adhesion. In addition, the surface wettability and Ra can be effectively controlled by regulating the current density. Furthermore, the surface maintained its superhydrophobicity after several mechanical tests, such as finger-wipe, knife-scratch, sand abrasion, and sandpaper abrasion, indicating that the surface possessed good mechanical stability. Also, the surface has superamphiphobic properties because its outermost surface contains −CF2− and −CF3 groups, possessing excellent acidic, alkaline, and oil repellency. Surprisingly, the surface still exhibited excellent self-cleaning ability even after 50 abrasion cycles with sandpaper and oil contamination. Such an ultrarobust self-cleaning surface is promising for large-scale applications using copper substrates. 16578


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Rough Structure of Electrodeposition as a Template for an Ultrarobust

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