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Simple fabrication of superamphiphobic copper surfaces with multilevel structures
Colloids and Surfaces A 539 (2018) 11–17
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Colloids and Surfaces A journal homepage: www.elsevier.com/locate/colsurfa
Simple fabrication of superamphiphobic copper surfaces with multilevel structures Qiuying Wena,b, Fei Guoa,b, Yubing Penga,b, Zhiguang Guoa,b,
T
⁎
a
Hubei Collaborative Innovation Centre for Advanced Organic Chemical Materials and Ministry of Education Key Laboratory for the Green Preparation and Application of Functional Materials, Hubei University, Wuhan 430062, People’s Republic of China b State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, People’s Republic of China
G RA P H I C A L AB S T R A C T Herein, we reported the simple fabrication of the superamphiphobic copper surfaces via a simple oxidation process and displacement reaction to create multilevel structures, followed by modification. The prepared superamphiphobic copper surfaces exhibit high contact angles (> 150°) of water, various oil and ethanol-water droplets with different mass fraction, which have great self-cleaning, oil resistant, anticorrosion properties.
A R T I C L E I N F O
A B S T R A C T
Keywords: Superamphiphobic Copper Self-cleaning Oil-resistant Corrosion resistance
Copper is widely used in various fields owing to its great electrical and thermal conductivity and so on. Once Coper is endowed with other properties, such as superamphiphobic, and the corresponding applications can be broadened. Hereby, we presented a convenient and cost-effective method to fabricate a superamphiphobic surface on the copper sheet. By virtue of scanning electron microscope (SEM), it is clear that hierarchical structures composed of micrometer-scale flake-like CuO and nanometer-scale Ag particles were formed on the copper surface by an alkali assistant oxidation process and a displacement reaction. After chemical modification of 1H,1H,2H,2H-perfluorodecanethiol, the surface with dual-scale structures was endowed with super-repellent ability towards water and several organic liquids with much lower surface tension, such as diesel, crude oil, colza oil and so on. Such superamphiphobic copper surfaces exhibit high contact angles (> 150°) of water, various oil, and ethanol-water (with different mass fraction) droplets, as well as corresponding low sliding angles (< 10°),
⁎ Corresponding author at: Hubei Collaborative Innovation Centre for Advanced Organic Chemical Materials and Ministry of Education Key Laboratory for the Green Preparation and Application of Functional Materials, Hubei University, Wuhan 430062, People’s Republic of China. E-mail address: [email protected] (Z. Guo).
https://doi.org/10.1016/j.colsurfa.2017.12.007 Received 28 October 2017; Received in revised form 29 November 2017; Accepted 1 December 2017 0927-7757/ © 2017 Elsevier B.V. All rights reserved.
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which possess excellent self-cleaning and oil-resistant properties. In addition, enhanced corrosion resistance of the as-prepared surface was found in potential-dynamic polarization measurement.
1. Introduction
[38,39]. Based on this, the F-rich thiol was introduced to the copper substrate to lower the surface energy. In this study, in order to get a convenient approach to equip the copper with better performances, such as oil resistance, anticorrosion and so on, the superamphiphobic copper surface was prepared through an oxidation process and a displacement reaction to obtain multilevel structures (CuO/Ag multilevel structures), followed by chemical modification of 1H, 1H,2H, 2H-perfluorodecanethiol. The overall fabrication process time is less than 3 h, which is time-saving. Importantly, without the procedure of immersing in the AgNO3 solution to obtain multilevel structures, the superhydrophobic copper surface was only prepared. The superamphiphobic copper surface exhibits high water contact angle (WCA) more than 150° and low sliding angle (SA) less than 10°. In addition, it also shows high oil contact angle (OCA) more than 150° and low sliding angle (SA) less than 10°. The great anticorrosion resistance of the superamphiphobic surface was tested via electrochemical method. It is proved that the prepared superamphiphobic surface may have potential applications in self-cleaning, oil transportation, corrosion resistance, oil resistance, and so on.
Inspired from nature, by recognizing the roles of the two key factors, appropriate roughness and low-surface-energy chemistry composition [1–3], superhydrophobicity has been widely investigated and achieved on various material surfaces due to its numerous functions including drag reduction [4], self-cleaning property [5–7], anti-icing [8], oil/ water separation [9–11], and so on. Among these materials with antiwetting behavior, superhydrophobic metallic materials have attracted increasing interests because metal substrate is more readily to construct rough structure than other materials and superhydrophobicity can greatly facilitate the metallic anticorrosion performance and prolong service life [12,13]. For examples, Cho and co-workers fabricated a superhydrophobic steel surface with improved anticorrosion performance through simply coating superhydrophobic nanocomposites on the bare steel [14]. Liu et al. reported a one-step electrodeposition method to prepare biomimetic superhydrophobic magnesium alloy with corrosion resistance ability [15]. Brassard and co-workers electrodeposited a thin Zn film on steel substrates, followed by modification with ultra-thin films of commercial silicone rubber, getting superhydrophobic surface for prevention of corrosion [16]. At the same time, copper, as an important engineering metallic material, has been widely used in many industrial applications owing to its excellent properties, such as great ductility, high electrical and thermal conductivity. However, when exposed to high humidity or elevated temperature, it can be easily contaminated and corroded despite of its good corrosion resistance, which greatly hamper its performance. Superhydrophobicity offers an efficient strategy to protect copper surface from corrosion and many superhydrophobic copper surfaces have been prepared for broad applications [17–23]. But, superhydrophobic copper surface only exhibits self-cleaning and antifouling abilities towards aqua-based liquid and cannot exhibit oil repellency property due to much lower surface tension of oil, which would seriously hinder applications of superhydrophobic copper such as oil resistance, oil transportation, and so on. Therefore, it is necessary to prepare superamphiphobic copper surface. However, compared to superhydrophobic surface, the demand on constructing superamphiphobic surface is higher. It is prerequisite to construct smaller or more special structure and to be modified with much lower surface energy. Aiming at these problems, many research groups have tried various techniques to create superamphiphobic surfaces and some promising results have been reported [24–28]. It is found that some special morphologies with dual-scale roughness (such as micrometerscale and nanometer-scale surface roughness) make great sense to enhance the superamphiphobic property [29]. By controlling both surface energy and appropriate roughness, superamphiphobic surface can be fabricated [30–35]. Based on that, some superamphiphobic copper have been successfully prepared and researchers have reported a few methods for their development [34,36,37]. For examples, Li et al. prepared superamphiphobic CuO with hierarchical flower-like structures via electrodeposition and solution-immersion process, followed by fluorinated modification for 7 days [24]. Li and co-workers fabricated superamphiphobic surface on a copper substrate through chemical base deposition method and perfluorothiolate modification [36]. However, most of the preparation methods involved in complex steps and are time-consuming. So, it is necessary to obtain superamphiphobicity on copper surface through convenient and time-saving ways to meet the demand of industrial applications. It has been reported that the transition metals and their oxides (Groups VIII and IB such as Cu and Ag) can easily coordinate with thiols
2. Experimental section 2.1. Materials Copper sheet was used after cleaning process. Anhydrous ethanol, sodium hydroxide (NaOH), ammonium persulfate ((NH4)2S2O8) and silver nitrate (AgNO3) were analytical grade reagents and were used as received. 1H,1H,2H,2H-perfluorodecanethiol was used as a low-surface-energy modifier. 2.2. Fabrication of CuO flake-like structures The copper sheet (2 × 3 cm) was ultrasonically cleaned by ethanol and deionized water respectively and dried at room temperature. Then the copper sheet was immersed in 20 mL aqueous solution including NaOH (1 mol/L) and (NH4)2S2O8 (0.05 mol/L) in water bath of 60 °C for 30 min. After the oxidation, the copper sheet was taken out and washed with water, followed by drying at 60 °C. 2.3. Fabrication of CuO/Ag multilevel structures The copper sheet with CuO flake-like structures was immersed in the 20 mL AgNO3 solution (1 g/L) for 30 min at room temperature. Then the copper sheet was taken out and dried at 60 °C for 30 min. In order to remove the residual reagent, the dried copper sheet was washed with deionized water and dried at room temperature to obtain CuO/Ag multilevel structures. 2.4. Modification The copper sheets coated with CuO/Ag multilevel structures were immersed into ethanol solution of 1H,1H,2H,2H-perfluorodecanethiol for 30 min at room temperature. Afterwards, the copper sheets were washed with ethanol and dried at room temperature to obtain superamphiphobic copper surface. As a contrast, before immersed in the AgNO3 solution, the copper sheet with CuO flake-like structures was directly immersed into the ethanol solution of 1H,1H,2H,2H-perfluorodecanethiol for 30 min to obtain superhydrophobic copper surface. 12
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were presented in Fig. 1 and 2. After oxidation, the copper sheet was covered by micro/nano scaled CuO flake-like structures (Fig. 1a). After modified with 1H,1H,2H,2H-perfluorodecanethiol, the CuO flake-like structures turned into micronipples and nanorods structures which were similar to the surface structure of lotus leaf (Fig. 1b) [40]. The micronipples and nanorods structures combined with the low-surfaceenergy material lead to the great superhydrophobicity with WCA more than 160° (Fig. 1c). At the same time, it exhibits oleophobicity with OCA about 104° (Fig. 1d). Compared to this superhydrophobic copper sheet, the superamphiphobic copper surface was obtained through further immersing the oxidized copper sheet into AgNO3 solution to create multilevel structures followed by the chemical modification. In the AgNO3 solution, Ag particles would grow on the copper sheet surface through simple displacement reaction and some Ag particles gathered together to form coral-like aggregation (Fig. 2a1). Importantly, the copper sheet was covered by not only micro/nano scaled CuO flake-like structures but also Ag nanoparticles (Fig. 2a, a1 and a2). Additionally, after chemical modification, the CuO flake-like structures has been transformed to uniform micronipples and nanorods structures (Fig. 2b2) and coral-like Ag aggregation has been changed into re-entrant structure (Fig. 2b1), leading to the development of multilevel structures (Fig. 2b). Briefly, after chemistry modification of the same low-surface-energy material, the superhydrophobic copper sheet that has the similar structure to lotus leaf cannot extremely repel oils. Nevertheless, the CuO/Ag coating with the special multilevel structures exhibits both superhydrophobicity and superoleophobicity.
2.5. Characterization The morphology of the samples was observed on a field emission scanning electron microscope (FESEM, JSM-6701F) with Au-sputtered specimens. As for the component analysis, X-ray photoelectron spectroscopy (XPS, Thermo Scientific ESCALAB 250Xi) measurements were made using the Al Ka line as the excitation source. The element distribution maps of the prepared samples were obtained by energy dispersive spectroscopy (EDS, Kevex). X-ray diffraction (XRD, X’SPERT PRO) analysis was also conducted to testify the chemical compositions. CAs (water, ethanolwater mixture, and various oils) were measured using a CA meter (JC2000D) with about 5 μL liquid droplets at ambient temperature. The average CA values were obtained via measuring each sample at three different positions. SAs were measured on the CA meter using 5–7 μL liquid droplets. In order to test the anticorrosion function, the polarization measurements were conducted in the 3.5 wt.% NaCl aqueous solution at room temperature via a three-electrode system, in which the prepared samples, platinum slice, and the saturated calomel electrode were used as working electrode, counter electrode, and reference electrode, respectively. Besides, the exposed area of the working electrode is 6 cm2. 3. Results and discussion 3.1. Preparation of superamphiphobic copper surface SEM images of the copper sheet processed with different procedures
Fig. 1. SEM images of CuO flake-like structures on the copper surface before (a) and after (b) chemical modification. (c) WCA (left) and OCA (diesel, right) on the superhydrophobic copper sheet surface.
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Fig. 2. SEM images of CuO/Ag multilevel structures on the copper surface before (a) and after (b) chemical modification. (c-e) EDS analysis of the superamphiphobic copper surface.
1H,1H,2H,2H-perfluorodecanethiol. From the SEM-EDS mapping in Fig. 2c and e, each element is uniformly distributed on the surface of the superamphiphobic copper sheet, indicating that the Ag particles uniformly grow on the oxidized copper sheet after the displacement
EDS analysis was conducted to investigate the chemical compositions of the samples. As shown in Fig. 2d, the main elemental compositions of the superamphiphobic copper sheet are Cu, Ag, O, F, C, and S. The appearance of F and S is attributed to the successful modification of 14
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Fig. 3. (a) XPS spectra of the original copper sheet (curve 1), the oxidized copper sheet before (curve 2) and after immersing in the AgNO3 solution (curve 3) and then chemical modification (curve 4). (b) Photographs of various liquid droplets on the superamphiphobic copper sheet. (c) CAs of the superamphiphobic copper sheet.
3.2. Self-cleaning and oil-resistant properties of the superamphiphobic copper surface
reaction. In contrast, EDS analysis of the superhydrophobic copper sheet resemble that of the superamphiphobic copper sheet except no Ag (Fig. S1). In order to further prove the chemical composition, XPS measurements of the copper sheet processed with different procedure were conducted (Fig. 3a). The original copper sheet contains Cu, O, and C (curve 1). In contrast, the O ratio of the oxidized copper sheet is obviously increased (curve 2). After immersing in the AgNO3 solution, the appearance of the Ag peak (curve 3) confirms the successful introduction of Ag particles via displacement reaction. Furthermore, the modification of 1H,1H,2H,2H-perfluorodecanethiol brings about F and S (curve 4 and Fig. S2). In addition, XPS spectrum of the superhydrophobic copper sheet is shown in Fig. S3, being consistent with the EDS analysis. Fig. S4 shows XRD patterns of the copper sheet before and after oxidation. As seen in Fig. S4a, the diffraction peaks are indexed to Cu on the original copper sheet. After oxidation, the additional diffraction peaks are ascribed to the orientation of (1 0), (−1 1), and (2 0) of CuO, further proving that the flake-like structures on the copper sheet are CuO after oxidation reaction (Fig. S4b). The CuO is attributed to the Cu(OH)2 decomposing in the oxidation process and the orientation of (−1 1), (2 0) of CuO is originated from the orientation (1 0), (0 2) of Cu(OH)2 through dehydration [24], The prepared copper sheet with multilevel structures exhibits great superhydrophobicity and superoleophobicity (Fig. 3b and c). The WCA on the superamphiphobic copper sheet is about 158° and the OCAs toward diesel, crude oil, colza oil and hexadecane are all larger than 150°. In addition, the ethanol-water droplet with different mass ratios can also display a spherical shape on the superamphiphobic copper sheet and the CA with 30 wt.% ethanol is about 152.3°. When the mass ratio of ethanol is increased to 50 wt.%, the corresponding CA is about 148.3°. It is indicated that the prepared superamphiphobic copper sheet mostly repels liquid droplets that possess surface tension larger than the 50 wt.% ethanol-water mixture (28.51 mN/m) [41–43]. The SAs of various liquid droplets (water, diesel, crude oil, colza oil, hexadecane, 10 wt.% and 30 wt.% ethanol-water mixtures) are all less than 10° (Table S1 and Movies S1–S7).
It is generally known that the lotus leaf possesses great self-cleaning performance owing to its superhydrophobicity. When water droplets roll off, the dust on lotus leaf surface would be taken away. Compared to the lotus leaf, the superamphiphobic copper sheet shows “selfcleaning” ability toward both water and oil due to a high ratio of air trapped in the interface between superamphiphobic surface and liquid, resulting in that the liquid droplet can be suspended with low adhesion. Just as shown in Fig. S5, based on the air layer trapped on the superamphiphobic copper sheet, there was a stable silver mirror phenomenon when it was immersed into water and diesel, respectively. As shown in Fig. 4a, some dusts are placed on the superamphiphobic copper sheet with a slight inclination. Then, clean water is continuously dripped down and water can smoothly roll down and take the adhered dust away, leading to the surface restore to clean (Movie S8). In addition, the polluted superamphiphobic copper sheet by dust can also be cleaned by the rolling oil droplets (Fig. 4b and Movie S9). In order to demonstrate the oil-resistant performance of the superamphiphobic copper sheet, the oil-resistant tests were conducted by immersing the prepared superhydrophobic and superamphiphobic copper sheets into crude oil and taking it out, respectively. The test results are shown in Fig. 4c and d. It can be found that the superhydrophobic copper sheet was readily polluted by the crude oil (Fig. 4c and Movie S10). On the contrary, the superamphiphobic copper sheet still remained clean (Fig. 4d and Movie S11), showing excellent self-cleaning and oil-resistant performance. These self-cleaning and oil-resistant properties of the superamphiphobic copper are of great significance for practical applications. 3.3. Anticorrosion ability and durability of the superamphiphobic copper surface When the superamphiphobic surface contacts water or some oil, the air layer trapped among micro/nanostructures would act an effective 15
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Fig. 4. Self-cleaning tests of the superamphiphobic copper sheet on the slightly inclined glass sheet and the dust as contaminant is taken away by the water droplets (a) and oil droplets (b) respectively. Oil-resistant tests of the superhydrophobic copper sheet (c) and superamphiphobic copper sheet (d) via immersing them in the crude oil.
excellent corrosion resistance, which may have potential application in different fields. In addition, in order to test the durability of the superamphiphobic copper sheet, the prepared superamphiphobic copper sheet has been placed for ∼50 days at room temperature. After that, WCA and OCA of the superamphiphobic copper sheet were measured again to characterize the water and oil repellence. Diesel was chosen as typical oil.
barrier between substrates and liquids. Therefore, the superamphiphobic surface possesses waterproof, oil proof function, and good anticorrosion properties. In order to prove the corrosion resistance of the superamphiphobic copper sheet, the salt aqueous solution (3.5 wt. %) was used as corrosion solution to testify the anticorrosion performance of the bare and prepared copper sheets by the potentiodynamic polarization measurement (Table 1 and Fig. 5). It is found that the corrosion current (icorr) of the superamphiphobic and superhydrophobic copper sheets all decrease by approximately one order of magnitude, compared to that of the bare copper sheet. Besides, the superamphiphobic copper sheet exhibits smaller icorr value than the superhydrophobic copper sheet, indicating that the superamphiphobic copper sheet has greater anticorrosion ability. It may be attributed to the higher ratio air trapped in the special multilevel structures of the superamphiphobic copper sheet. According to the corrosion characteristics, the prepared superamphiphobic copper sheet exhibits
Table 1 Corrosion characteristics of the bare copper sheet, the superhydrophobic copper sheet and the superamphiphobic copper sheet. Samples Bare copper sheet Superhydrophobic copper sheet Superamphiphobic copper sheet
icorr (A)
Ecorr (V) −5
2.164 × 10 6.934 × 10−6 9.669 × 10−6
−0.2966 −0.2510 −0.2015
Fig. 5. Potentiodynamic polarization curves of the bare copper sheet, the superhydrophobic copper sheet, and the superamphiphobic copper sheet.
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As shown in Fig. S6, the superamphiphobic copper sheet still exhibits excellent superhydrophobicity with WCA of ∼159° and good oleophobicity with OCA of ∼144°. It is indicated that the prepared superamphiphobic copper sheet relatively possesses good durability.
[15]
[16]
4. Conclusions
[17]
In summary, the superamphiphobic copper sheet has been prepared by a simple oxidation process and displacement reaction followed by chemical modification. Comparing the prepared superhydrophobic copper surface with superamphiphobic copper surface, we can find that the multilevel structures play an important role in the construction of the superamphiphobic surface. The obtained superamphiphobic copper sheet exhibits great self-cleaning, oil-resistant, and anticorrosion properties. Even though some superamphiphobic copper with multilevel structures have been constructed, it is generally time-consuming and multi-step to get dual-scale roughness and low-surface-energy modification [24,32,44]. There is still a big challenge to prepare superamphiphobic surface in more convenient ways. This work offers a simple and cost-effective way to prepare superamphiphobic surface that may provide prospects for facilitating their versatility and practicability in potential applications in many fields such as oil transportation, oil resistance, and corrosion resistance. In addition, this approach may also be extended to other metallic materials in practical applications.
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Acknowledgement
[27]
This study is supported by the National Nature Science Foundation of China (No. 51522510, 51675513 and 51735013).
[28] [29]
Appendix A. Supplementary data [30]
Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.colsurfa.2017.12.007.
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Contents lists available at ScienceDirect
Colloids and Surfaces A journal homepage: www.elsevier.com/locate/colsurfa
Simple fabrication of superamphiphobic copper surfaces with multilevel structures Qiuying Wena,b, Fei Guoa,b, Yubing Penga,b, Zhiguang Guoa,b,
T
⁎
a
Hubei Collaborative Innovation Centre for Advanced Organic Chemical Materials and Ministry of Education Key Laboratory for the Green Preparation and Application of Functional Materials, Hubei University, Wuhan 430062, People’s Republic of China b State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, People’s Republic of China
G RA P H I C A L AB S T R A C T Herein, we reported the simple fabrication of the superamphiphobic copper surfaces via a simple oxidation process and displacement reaction to create multilevel structures, followed by modification. The prepared superamphiphobic copper surfaces exhibit high contact angles (> 150°) of water, various oil and ethanol-water droplets with different mass fraction, which have great self-cleaning, oil resistant, anticorrosion properties.
A R T I C L E I N F O
A B S T R A C T
Keywords: Superamphiphobic Copper Self-cleaning Oil-resistant Corrosion resistance
Copper is widely used in various fields owing to its great electrical and thermal conductivity and so on. Once Coper is endowed with other properties, such as superamphiphobic, and the corresponding applications can be broadened. Hereby, we presented a convenient and cost-effective method to fabricate a superamphiphobic surface on the copper sheet. By virtue of scanning electron microscope (SEM), it is clear that hierarchical structures composed of micrometer-scale flake-like CuO and nanometer-scale Ag particles were formed on the copper surface by an alkali assistant oxidation process and a displacement reaction. After chemical modification of 1H,1H,2H,2H-perfluorodecanethiol, the surface with dual-scale structures was endowed with super-repellent ability towards water and several organic liquids with much lower surface tension, such as diesel, crude oil, colza oil and so on. Such superamphiphobic copper surfaces exhibit high contact angles (> 150°) of water, various oil, and ethanol-water (with different mass fraction) droplets, as well as corresponding low sliding angles (< 10°),
⁎ Corresponding author at: Hubei Collaborative Innovation Centre for Advanced Organic Chemical Materials and Ministry of Education Key Laboratory for the Green Preparation and Application of Functional Materials, Hubei University, Wuhan 430062, People’s Republic of China. E-mail address: [email protected] (Z. Guo).
https://doi.org/10.1016/j.colsurfa.2017.12.007 Received 28 October 2017; Received in revised form 29 November 2017; Accepted 1 December 2017 0927-7757/ © 2017 Elsevier B.V. All rights reserved.
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which possess excellent self-cleaning and oil-resistant properties. In addition, enhanced corrosion resistance of the as-prepared surface was found in potential-dynamic polarization measurement.
1. Introduction
[38,39]. Based on this, the F-rich thiol was introduced to the copper substrate to lower the surface energy. In this study, in order to get a convenient approach to equip the copper with better performances, such as oil resistance, anticorrosion and so on, the superamphiphobic copper surface was prepared through an oxidation process and a displacement reaction to obtain multilevel structures (CuO/Ag multilevel structures), followed by chemical modification of 1H, 1H,2H, 2H-perfluorodecanethiol. The overall fabrication process time is less than 3 h, which is time-saving. Importantly, without the procedure of immersing in the AgNO3 solution to obtain multilevel structures, the superhydrophobic copper surface was only prepared. The superamphiphobic copper surface exhibits high water contact angle (WCA) more than 150° and low sliding angle (SA) less than 10°. In addition, it also shows high oil contact angle (OCA) more than 150° and low sliding angle (SA) less than 10°. The great anticorrosion resistance of the superamphiphobic surface was tested via electrochemical method. It is proved that the prepared superamphiphobic surface may have potential applications in self-cleaning, oil transportation, corrosion resistance, oil resistance, and so on.
Inspired from nature, by recognizing the roles of the two key factors, appropriate roughness and low-surface-energy chemistry composition [1–3], superhydrophobicity has been widely investigated and achieved on various material surfaces due to its numerous functions including drag reduction [4], self-cleaning property [5–7], anti-icing [8], oil/ water separation [9–11], and so on. Among these materials with antiwetting behavior, superhydrophobic metallic materials have attracted increasing interests because metal substrate is more readily to construct rough structure than other materials and superhydrophobicity can greatly facilitate the metallic anticorrosion performance and prolong service life [12,13]. For examples, Cho and co-workers fabricated a superhydrophobic steel surface with improved anticorrosion performance through simply coating superhydrophobic nanocomposites on the bare steel [14]. Liu et al. reported a one-step electrodeposition method to prepare biomimetic superhydrophobic magnesium alloy with corrosion resistance ability [15]. Brassard and co-workers electrodeposited a thin Zn film on steel substrates, followed by modification with ultra-thin films of commercial silicone rubber, getting superhydrophobic surface for prevention of corrosion [16]. At the same time, copper, as an important engineering metallic material, has been widely used in many industrial applications owing to its excellent properties, such as great ductility, high electrical and thermal conductivity. However, when exposed to high humidity or elevated temperature, it can be easily contaminated and corroded despite of its good corrosion resistance, which greatly hamper its performance. Superhydrophobicity offers an efficient strategy to protect copper surface from corrosion and many superhydrophobic copper surfaces have been prepared for broad applications [17–23]. But, superhydrophobic copper surface only exhibits self-cleaning and antifouling abilities towards aqua-based liquid and cannot exhibit oil repellency property due to much lower surface tension of oil, which would seriously hinder applications of superhydrophobic copper such as oil resistance, oil transportation, and so on. Therefore, it is necessary to prepare superamphiphobic copper surface. However, compared to superhydrophobic surface, the demand on constructing superamphiphobic surface is higher. It is prerequisite to construct smaller or more special structure and to be modified with much lower surface energy. Aiming at these problems, many research groups have tried various techniques to create superamphiphobic surfaces and some promising results have been reported [24–28]. It is found that some special morphologies with dual-scale roughness (such as micrometerscale and nanometer-scale surface roughness) make great sense to enhance the superamphiphobic property [29]. By controlling both surface energy and appropriate roughness, superamphiphobic surface can be fabricated [30–35]. Based on that, some superamphiphobic copper have been successfully prepared and researchers have reported a few methods for their development [34,36,37]. For examples, Li et al. prepared superamphiphobic CuO with hierarchical flower-like structures via electrodeposition and solution-immersion process, followed by fluorinated modification for 7 days [24]. Li and co-workers fabricated superamphiphobic surface on a copper substrate through chemical base deposition method and perfluorothiolate modification [36]. However, most of the preparation methods involved in complex steps and are time-consuming. So, it is necessary to obtain superamphiphobicity on copper surface through convenient and time-saving ways to meet the demand of industrial applications. It has been reported that the transition metals and their oxides (Groups VIII and IB such as Cu and Ag) can easily coordinate with thiols
2. Experimental section 2.1. Materials Copper sheet was used after cleaning process. Anhydrous ethanol, sodium hydroxide (NaOH), ammonium persulfate ((NH4)2S2O8) and silver nitrate (AgNO3) were analytical grade reagents and were used as received. 1H,1H,2H,2H-perfluorodecanethiol was used as a low-surface-energy modifier. 2.2. Fabrication of CuO flake-like structures The copper sheet (2 × 3 cm) was ultrasonically cleaned by ethanol and deionized water respectively and dried at room temperature. Then the copper sheet was immersed in 20 mL aqueous solution including NaOH (1 mol/L) and (NH4)2S2O8 (0.05 mol/L) in water bath of 60 °C for 30 min. After the oxidation, the copper sheet was taken out and washed with water, followed by drying at 60 °C. 2.3. Fabrication of CuO/Ag multilevel structures The copper sheet with CuO flake-like structures was immersed in the 20 mL AgNO3 solution (1 g/L) for 30 min at room temperature. Then the copper sheet was taken out and dried at 60 °C for 30 min. In order to remove the residual reagent, the dried copper sheet was washed with deionized water and dried at room temperature to obtain CuO/Ag multilevel structures. 2.4. Modification The copper sheets coated with CuO/Ag multilevel structures were immersed into ethanol solution of 1H,1H,2H,2H-perfluorodecanethiol for 30 min at room temperature. Afterwards, the copper sheets were washed with ethanol and dried at room temperature to obtain superamphiphobic copper surface. As a contrast, before immersed in the AgNO3 solution, the copper sheet with CuO flake-like structures was directly immersed into the ethanol solution of 1H,1H,2H,2H-perfluorodecanethiol for 30 min to obtain superhydrophobic copper surface. 12
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were presented in Fig. 1 and 2. After oxidation, the copper sheet was covered by micro/nano scaled CuO flake-like structures (Fig. 1a). After modified with 1H,1H,2H,2H-perfluorodecanethiol, the CuO flake-like structures turned into micronipples and nanorods structures which were similar to the surface structure of lotus leaf (Fig. 1b) [40]. The micronipples and nanorods structures combined with the low-surfaceenergy material lead to the great superhydrophobicity with WCA more than 160° (Fig. 1c). At the same time, it exhibits oleophobicity with OCA about 104° (Fig. 1d). Compared to this superhydrophobic copper sheet, the superamphiphobic copper surface was obtained through further immersing the oxidized copper sheet into AgNO3 solution to create multilevel structures followed by the chemical modification. In the AgNO3 solution, Ag particles would grow on the copper sheet surface through simple displacement reaction and some Ag particles gathered together to form coral-like aggregation (Fig. 2a1). Importantly, the copper sheet was covered by not only micro/nano scaled CuO flake-like structures but also Ag nanoparticles (Fig. 2a, a1 and a2). Additionally, after chemical modification, the CuO flake-like structures has been transformed to uniform micronipples and nanorods structures (Fig. 2b2) and coral-like Ag aggregation has been changed into re-entrant structure (Fig. 2b1), leading to the development of multilevel structures (Fig. 2b). Briefly, after chemistry modification of the same low-surface-energy material, the superhydrophobic copper sheet that has the similar structure to lotus leaf cannot extremely repel oils. Nevertheless, the CuO/Ag coating with the special multilevel structures exhibits both superhydrophobicity and superoleophobicity.
2.5. Characterization The morphology of the samples was observed on a field emission scanning electron microscope (FESEM, JSM-6701F) with Au-sputtered specimens. As for the component analysis, X-ray photoelectron spectroscopy (XPS, Thermo Scientific ESCALAB 250Xi) measurements were made using the Al Ka line as the excitation source. The element distribution maps of the prepared samples were obtained by energy dispersive spectroscopy (EDS, Kevex). X-ray diffraction (XRD, X’SPERT PRO) analysis was also conducted to testify the chemical compositions. CAs (water, ethanolwater mixture, and various oils) were measured using a CA meter (JC2000D) with about 5 μL liquid droplets at ambient temperature. The average CA values were obtained via measuring each sample at three different positions. SAs were measured on the CA meter using 5–7 μL liquid droplets. In order to test the anticorrosion function, the polarization measurements were conducted in the 3.5 wt.% NaCl aqueous solution at room temperature via a three-electrode system, in which the prepared samples, platinum slice, and the saturated calomel electrode were used as working electrode, counter electrode, and reference electrode, respectively. Besides, the exposed area of the working electrode is 6 cm2. 3. Results and discussion 3.1. Preparation of superamphiphobic copper surface SEM images of the copper sheet processed with different procedures
Fig. 1. SEM images of CuO flake-like structures on the copper surface before (a) and after (b) chemical modification. (c) WCA (left) and OCA (diesel, right) on the superhydrophobic copper sheet surface.
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Fig. 2. SEM images of CuO/Ag multilevel structures on the copper surface before (a) and after (b) chemical modification. (c-e) EDS analysis of the superamphiphobic copper surface.
1H,1H,2H,2H-perfluorodecanethiol. From the SEM-EDS mapping in Fig. 2c and e, each element is uniformly distributed on the surface of the superamphiphobic copper sheet, indicating that the Ag particles uniformly grow on the oxidized copper sheet after the displacement
EDS analysis was conducted to investigate the chemical compositions of the samples. As shown in Fig. 2d, the main elemental compositions of the superamphiphobic copper sheet are Cu, Ag, O, F, C, and S. The appearance of F and S is attributed to the successful modification of 14
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Fig. 3. (a) XPS spectra of the original copper sheet (curve 1), the oxidized copper sheet before (curve 2) and after immersing in the AgNO3 solution (curve 3) and then chemical modification (curve 4). (b) Photographs of various liquid droplets on the superamphiphobic copper sheet. (c) CAs of the superamphiphobic copper sheet.
3.2. Self-cleaning and oil-resistant properties of the superamphiphobic copper surface
reaction. In contrast, EDS analysis of the superhydrophobic copper sheet resemble that of the superamphiphobic copper sheet except no Ag (Fig. S1). In order to further prove the chemical composition, XPS measurements of the copper sheet processed with different procedure were conducted (Fig. 3a). The original copper sheet contains Cu, O, and C (curve 1). In contrast, the O ratio of the oxidized copper sheet is obviously increased (curve 2). After immersing in the AgNO3 solution, the appearance of the Ag peak (curve 3) confirms the successful introduction of Ag particles via displacement reaction. Furthermore, the modification of 1H,1H,2H,2H-perfluorodecanethiol brings about F and S (curve 4 and Fig. S2). In addition, XPS spectrum of the superhydrophobic copper sheet is shown in Fig. S3, being consistent with the EDS analysis. Fig. S4 shows XRD patterns of the copper sheet before and after oxidation. As seen in Fig. S4a, the diffraction peaks are indexed to Cu on the original copper sheet. After oxidation, the additional diffraction peaks are ascribed to the orientation of (1 0), (−1 1), and (2 0) of CuO, further proving that the flake-like structures on the copper sheet are CuO after oxidation reaction (Fig. S4b). The CuO is attributed to the Cu(OH)2 decomposing in the oxidation process and the orientation of (−1 1), (2 0) of CuO is originated from the orientation (1 0), (0 2) of Cu(OH)2 through dehydration [24], The prepared copper sheet with multilevel structures exhibits great superhydrophobicity and superoleophobicity (Fig. 3b and c). The WCA on the superamphiphobic copper sheet is about 158° and the OCAs toward diesel, crude oil, colza oil and hexadecane are all larger than 150°. In addition, the ethanol-water droplet with different mass ratios can also display a spherical shape on the superamphiphobic copper sheet and the CA with 30 wt.% ethanol is about 152.3°. When the mass ratio of ethanol is increased to 50 wt.%, the corresponding CA is about 148.3°. It is indicated that the prepared superamphiphobic copper sheet mostly repels liquid droplets that possess surface tension larger than the 50 wt.% ethanol-water mixture (28.51 mN/m) [41–43]. The SAs of various liquid droplets (water, diesel, crude oil, colza oil, hexadecane, 10 wt.% and 30 wt.% ethanol-water mixtures) are all less than 10° (Table S1 and Movies S1–S7).
It is generally known that the lotus leaf possesses great self-cleaning performance owing to its superhydrophobicity. When water droplets roll off, the dust on lotus leaf surface would be taken away. Compared to the lotus leaf, the superamphiphobic copper sheet shows “selfcleaning” ability toward both water and oil due to a high ratio of air trapped in the interface between superamphiphobic surface and liquid, resulting in that the liquid droplet can be suspended with low adhesion. Just as shown in Fig. S5, based on the air layer trapped on the superamphiphobic copper sheet, there was a stable silver mirror phenomenon when it was immersed into water and diesel, respectively. As shown in Fig. 4a, some dusts are placed on the superamphiphobic copper sheet with a slight inclination. Then, clean water is continuously dripped down and water can smoothly roll down and take the adhered dust away, leading to the surface restore to clean (Movie S8). In addition, the polluted superamphiphobic copper sheet by dust can also be cleaned by the rolling oil droplets (Fig. 4b and Movie S9). In order to demonstrate the oil-resistant performance of the superamphiphobic copper sheet, the oil-resistant tests were conducted by immersing the prepared superhydrophobic and superamphiphobic copper sheets into crude oil and taking it out, respectively. The test results are shown in Fig. 4c and d. It can be found that the superhydrophobic copper sheet was readily polluted by the crude oil (Fig. 4c and Movie S10). On the contrary, the superamphiphobic copper sheet still remained clean (Fig. 4d and Movie S11), showing excellent self-cleaning and oil-resistant performance. These self-cleaning and oil-resistant properties of the superamphiphobic copper are of great significance for practical applications. 3.3. Anticorrosion ability and durability of the superamphiphobic copper surface When the superamphiphobic surface contacts water or some oil, the air layer trapped among micro/nanostructures would act an effective 15
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Fig. 4. Self-cleaning tests of the superamphiphobic copper sheet on the slightly inclined glass sheet and the dust as contaminant is taken away by the water droplets (a) and oil droplets (b) respectively. Oil-resistant tests of the superhydrophobic copper sheet (c) and superamphiphobic copper sheet (d) via immersing them in the crude oil.
excellent corrosion resistance, which may have potential application in different fields. In addition, in order to test the durability of the superamphiphobic copper sheet, the prepared superamphiphobic copper sheet has been placed for ∼50 days at room temperature. After that, WCA and OCA of the superamphiphobic copper sheet were measured again to characterize the water and oil repellence. Diesel was chosen as typical oil.
barrier between substrates and liquids. Therefore, the superamphiphobic surface possesses waterproof, oil proof function, and good anticorrosion properties. In order to prove the corrosion resistance of the superamphiphobic copper sheet, the salt aqueous solution (3.5 wt. %) was used as corrosion solution to testify the anticorrosion performance of the bare and prepared copper sheets by the potentiodynamic polarization measurement (Table 1 and Fig. 5). It is found that the corrosion current (icorr) of the superamphiphobic and superhydrophobic copper sheets all decrease by approximately one order of magnitude, compared to that of the bare copper sheet. Besides, the superamphiphobic copper sheet exhibits smaller icorr value than the superhydrophobic copper sheet, indicating that the superamphiphobic copper sheet has greater anticorrosion ability. It may be attributed to the higher ratio air trapped in the special multilevel structures of the superamphiphobic copper sheet. According to the corrosion characteristics, the prepared superamphiphobic copper sheet exhibits
Table 1 Corrosion characteristics of the bare copper sheet, the superhydrophobic copper sheet and the superamphiphobic copper sheet. Samples Bare copper sheet Superhydrophobic copper sheet Superamphiphobic copper sheet
icorr (A)
Ecorr (V) −5
2.164 × 10 6.934 × 10−6 9.669 × 10−6
−0.2966 −0.2510 −0.2015
Fig. 5. Potentiodynamic polarization curves of the bare copper sheet, the superhydrophobic copper sheet, and the superamphiphobic copper sheet.
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As shown in Fig. S6, the superamphiphobic copper sheet still exhibits excellent superhydrophobicity with WCA of ∼159° and good oleophobicity with OCA of ∼144°. It is indicated that the prepared superamphiphobic copper sheet relatively possesses good durability.
[15]
[16]
4. Conclusions
[17]
In summary, the superamphiphobic copper sheet has been prepared by a simple oxidation process and displacement reaction followed by chemical modification. Comparing the prepared superhydrophobic copper surface with superamphiphobic copper surface, we can find that the multilevel structures play an important role in the construction of the superamphiphobic surface. The obtained superamphiphobic copper sheet exhibits great self-cleaning, oil-resistant, and anticorrosion properties. Even though some superamphiphobic copper with multilevel structures have been constructed, it is generally time-consuming and multi-step to get dual-scale roughness and low-surface-energy modification [24,32,44]. There is still a big challenge to prepare superamphiphobic surface in more convenient ways. This work offers a simple and cost-effective way to prepare superamphiphobic surface that may provide prospects for facilitating their versatility and practicability in potential applications in many fields such as oil transportation, oil resistance, and corrosion resistance. In addition, this approach may also be extended to other metallic materials in practical applications.
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Acknowledgement
[27]
This study is supported by the National Nature Science Foundation of China (No. 51522510, 51675513 and 51735013).
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Appendix A. Supplementary data [30]
Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.colsurfa.2017.12.007.
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