One-Step Spray-Coating Process for the Fabrication of Colorful

Subscriber access provided by CMU Libraries - http://library.cmich.edu

Article

One-step spray-coating process for the fabrication of colorful superhydrophobic coatings with excellent corrosion resistance Jian Li, Runni Wu, Zhijiao Jing, Long Yan, Fei Zha, and Ziqiang Lei Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.5b02734 • Publication Date (Web): 14 Sep 2015 Downloaded from http://pubs.acs.org on September 15, 2015

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Langmuir is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 30

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

Langmuir

Colorful superhydrophobic anticorrosive coatings were fabricated by spraying various stearate suspensions onto metallic substrates, showing uniform and distinguishing colors.

ACS Paragon Plus Environment

Langmuir

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

One-step spray-coating process for the fabrication of colorful superhydrophobic coatings with excellent corrosion resistance Jian Li, * Runni Wu, ‡ Zhijiao Jing, ‡ Long Yan, Fei Zha and Ziqiang Lei * Key Laboratory of Eco-Environment-Related Polymer Materials, Ministry of Education of China, Key Laboratory of Gansu Polymer Materials, College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou 730070, China

*

Corresponding author. Tel.: +86 931 7971533. Tel.: +86 931 7970359. E-mail:[email protected] (J. Li), [email protected] (Z. Lei). ‡

These authors contributed equally. 1


Page 2 of 30

Page 3 of 30

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

Langmuir

Abstract: A simple method was used to generate colorful hydrophobic stearate particles via chemical reactions between inorganic salts and sodium stearate. Colored self-cleaning superhydrophobic coatings were prepared through a facile one-step spray-coating process by spraying the stearate particle suspensions onto stainless steel substrates. Furthermore, the colorful superhydrophobic coating maintains excellent chemical stability under both acidic and alkaline harsh circumstances. After being immersed in 3.5 wt% NaCl aqueous solution for one month, the as-prepared coatings still remain superhydrophobicity, however, lost the self-cleaning property with the sliding angle about 46 ± 3°. The corrosion behavior of the superhydrophobic coatings on Al substrate was characterized by the polarization curve and the electrochemical impedance spectroscopy (EIS). The electrochemical corrosion test results indicated that the superhydrophobic coatings possessed excellent corrosion resistance property, which could supply efficient and long-term preservation for the bare Al substrate. Keywords: superhydrophobic; colorful; stearate particles; corrosion resistance

2


Langmuir

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

1. Introduction Inspired by natural water-repellent surfaces derived from leaves of various plants, petals of several flowers and body structures of diverse insets, which possess contact angles (CAs) higher than 150°,1–3 artificial superhydrophobic surfaces have been prepared and received extensive attentions because of their remarkable significance in both fundamental research and potential industrial applications during the last decades, for example, self-cleaning,4 transparent coatings,5,6 anti-fogging,7 anti-corrosion,8–10 oil/water separation,11–13 selective transportation of microdroplets,14–16 and so forth. On the basis of the results of previous studies, the conventional approach of fabricating superhydrophobic surfaces involves two-steps: first creating a hierarchical rough surface and then modifying it with low energy materials.17,18 Therefore, if the two-steps involved in the preparation of traditional superhydrophobic surfaces could be accomplished in just one single step, the complexity of fabricating superhydrophobic surfaces would be eliminated.19–25 Herein, the superhydrophobic surfaces are fabricated using a facile one-step process through spraying the stearate hydrophobic particles onto stainless steel substrates. With respect to potential application of superhydrophobic surfaces, the diverse color appearance of superhydrophobic surfaces is as important as other properties in potential academic research and industrial applications. However, up to now, the preparation of colorful superhydrophobic coatings is still scarce due to difficult to alter their color appearance. Recently, a few groups have attempted to creat colorful superhydrophobic surfaces.26–29 For example, Ishizaki et al. obtained the color-tuned 3


Page 4 of 30

Page 5 of 30

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

Langmuir

anticorrosive magnesium alloy by a facile and cheap method.26 Ogihara et al. fabricated superhydrophobic colorful coatings through spraying pigment nanoparticle suspensions.27 Soler et al. prepared colored hydrophobic materials via grafting with polyfluorinated azo dyes.28 The aforementioned approaches to preparation of colored superhydrophobic coatings required either complex process control or pigments as raw materials. Therefore, it is great necessity to fabricate colorful superhydrophobic coatings by facile and inexpensive methods. In our work, various hydrophobic stearate particles are utilized to fabricate colored superhydrophobic coatings because of the simplicity in synthesis, low cost and widely tunable color appearances. Herein, the colorful superhydrophobic coatings were prepared through a simple one-step spray-coating process by spraying the stearate particle ethanol suspensions onto stainless steel substrates, showing uniform and distinguishing colors such as white, cinerous, purple, aurantium and blue respectively. Up to now, the preparation of colorful superhydrophobic coatings with considerably controllable color through colored stearate salts has never been reported. In addition, the method used here was simple, inexpensive and environmentally friendly, and the homogenesous stearate salts was used, avoiding pigments or dyes as raw materials. Besides, the colorful superhydrophobic coating maintains outstanding chemical stability under both acidic and alkaline harsh conditions. Furthermore, the corrosion behavior of the colored superhydrophobic coatings on Al substrate was also studied by the polarization curve and the electrochemical impedance spectroscopy (EIS). The results exhibit that the colorful superhydrophobic coatings possess outstanding corrosion resistance. 4


Langmuir

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

2. Experimental Section 2.1 Materials. Sodium stearate (NaSA), cupric acetate, iron (III) chloride hexahydrate, cobaltous (II) sulfate heptahydrate, chromium (III) chloride hexahydrate and zinc chloride were purchased from Tianjin Chemical Reagent Co., Ltd. and used as they were received. Stainless steel substrates were obtained from a local store and cleaned with acetone and ethanol respectively before use. 2.2 Preparation of colored particles and superhydrophobic coatings. Colored hydrophobic stearate particles were obtained by a simple chemical precipitation method through the chemical reactions in hot water between inorganic salts and organic salt of NaSA. In our study, it is the copper stearate (CuSA2) particle to be the represent sample of the colored hydrophobic stearate particle during the whole measurement. In detail, 8 mmol NaSA was firstly added to 80 mL hot water. After that, 4 mmol cupric acetate was dissolved in distilled water leading to transparent aqueous solutions. Then, the transparent aqueous solutions were added to the NaSA aqueous solution to generate CuSA2 particles. The other inorganic salts used in our work are iron (III) chloride hexahydrate, cobaltous (II) sulfate heptahydrate, chromium (III) chloride hexahydrate and zinc chloride respectively. The inorganic salts react with organic salts of NaSA to produce colored hydrophobic CuSA2, ferric stearate (FeSA3, 4 mmol iron (III) chloride hexahydrate:12 mmol NaSA), cobaltous stearate (CoSA2, 4 mmol cobaltous (II) sulfate heptahydrate:8 mmol NaSA), chromium stearate (CrSA3, 4 mmol chromium (III) chloride hexahydrate:12 mmol NaSA) and zinc stearate (ZnSA2, 4 mmol zinc chloride:8 mmol 5


Page 6 of 30

Page 7 of 30

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

Langmuir

NaSA) particles, respectively. In our study, it is the CuSA2 particle to be the represent sample of the hydrophobic colored stearate particles during the whole measurement. X-ray photoelectron spectroscopy (XPS) spectra and Fourier transform infrared spectrum (FT-IR) data (Figure S1 and S2a, Supporting Information) both confirmed the successful formation of CuSA2. The FT-IR spectra of other stearate salts were also shown in Figure S2, Supporting Information. The as-prepared single CuSA2 particle exhibits interesting flowerlike architecture composed of nanosheets with the average diameter of about 12 µm (Figure S3 and S4, the average diameter of other stearate particles were also shown in Figure S3 and S4, Supporting Information). Colored superhydrophobic coatings were prepared via a simple one-step spray-coating approach. Stearate particles (0.2 g) were dissloved in 20 mL ethanol to obtain uniform suspensions under magnetically stirring for 1h. Subsequently, the uniform suspensions were sprayed onto stainless steel substrates with 0.2 MPa compressed air gas using a spray gun with the nozzle diameter of about 0.8 mm, which was connected with an air compressor. The distance between the spray gun and the substrates was about 15 cm. Finally, the coatings were dried at ambient temperature for several hours in order to evaporate the ethanol completely. 2.3 Characterization. FT-IR spectroscopy was conducted with a Bio-Rad FTS-165 equipment. Dynamic light scattering (DLS) measurements were performed with Zetasizer Nanoseries (Malvern Instruments). XPS spectra were acquired on a PHI-5702 electron spectrometer using Mg Kα radiation as excitation source. The binding energies were referenced to the C 1s at 284.80 eV and the pass energy used 6


Langmuir

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

was 29.35 eV. A ratio Cu/C was calculated with the Shirley background. The morphological analysis was performed using a field emission scanning electron microscope (FE-SEM, Zeiss). Static water contact angle (CA) values were obtained using a Krüss DSA 100 apparatus at ambient temperature with 5 µL of deionized water (Millipore, >1.82 MΩ cm) on the sample surfaces. The sliding angles (SAs) were measured by slowly tilting the sample using the tilting table of the Krüss DSA 100 with 8 µL water droplet on it until the water droplet began to slide. The contact angle hysteresis (CAH) was computed by the difference between the values of the advancing contact angle (θadv) and receding contact angle (θrec). The water droplets with different pH values were measured on a pH meter (PHS-3C). Electrochemical measurements were carried out in 3.5 wt% NaCl corrosive solution at room temperature using a computer-controlled CHI660E electrochemical workstation, which was equipped with a three-electrode system with a saturated Ag/AgCl reference electrode, a platinum electrode as the counter electrode, and the samples (bare aluminum film and superhydrophobic coating formed on the aluminum film) as the working electrode. The surface area of the test samples open to the corrosive solution was 1 cm2. At first, the superhydrophobic coating formed on aluminum film was immersed in 3.5 wt% NaCl corrosive solution to establish the open circuit potential (Eocp). The polarization curves were obtained at a sweep rate of 5 mV s-1. The electrochemical impedance spectroscopy (EIS) measurements were conducted at Eocp in the frequency ranged from 10 mHz to 100 kHz with 2 cycles at each frequency using an ac perturbation of 5 mV. Impedance data were analyzed 7


Page 8 of 30

Page 9 of 30

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

Langmuir

using ZSimpWin software. 3. Results and Discussion Colored hydrophobic stearate particles were obtained through the chemical reactions in hot water between inorganic salts and sodium stearate (SA). Figure 1 shows the colorful superhydrophobic coatings prepared via a simple one-step spray-coating process. These coatings fabricated by spraying stearate particle ethanol suspensions on stainless steel substrates containing of copper stearate (CuSA2), ferric stearate (FeSA3), cobaltous stearate (CoSA2), chromium stearate (CrSA3) and zinc stearate (ZnSA2), show uniform, distinct colors covering the whole substrates, which are blue, aurantium, purple, cinerous and white, corresponding to CuSA2, FeSA3, CoSA2, CrSA3 and ZnSA2, respectively. Surface morphology of the as-prepared CuSA2 coating was investigated by FE-SEM. As shown in Figure 2a, the low magnification FE-SEM image exhibits that the surface are not smooth and a large number of particles agglomerate together to form larger microclusters. There are also numerous irregular void spaces among individual particles. Figure 2b exhibits image of a magnified microcluster, which is composed of some irregular micro-nanosheets as well as many messy gaps between the sheets, resulting in a larger fraction of air trapped in the irregular void spaces and grooves. And, the thickness of the coating is about 100 µm (Figure 2c). Therefore, this surface morphology is advantageous to lead to the excellent superhydrophobic and the low adhesive properties with a CA as high as 162 ± 1° and a SA as low as 4°. In this study, the CAH for the water droplets on the colorful coatings was also characterized. 8


Langmuir

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

Page 10 of 30

As listed in Table 1, it can be seen that all coatings exhibit large CAs (approximately 160°), low SAs (≤5°) and low CAH with water droplets easily rolling off the surfaces. Other colored coatings have similar morphologies because all coatings are prepared by the one-step spray-coating process of homologous particles. Table1.CAs and SAs of colorful superhydrophobic stearate coatings. CAH

SA

160.3 ± 2°

3.8

4

164.1 ± 2°

161.9 ± 2°

2.9

3

160.4 ± 1°

163.1 ± 2°

159.1 ± 2°

4

4

CrSA3

160.1 ± 1°

162.7 ± 2°

158.0 ± 2°

4.7

5

ZnSA2

159.8 ± 1°

161.4 ± 2°

155.6 ± 2°

5.8

5

Pigments

CA

θadv

CuSA2

162.1 ± 1°

164.1 ± 2°

FeSA3

160.6 ± 1°

CoSA2

θrec

Degree is the unit for all angles in the Table.

The superhydrophobic surfaces always performed durable resistance in different corrosive environments. In our work, it is the superhydrophobic CuSA2 coating to be the represent sample of the colorful superhydrophobic coatings during the whole measurement. Figure 3a shows the relationship between pH values of water droplet and the water CAs and SAs on the superhydrophobic CuSA2 coating. CA values on the superhydrophobic coating keep almost invariably within experimental error at all pH values of water droplet ranged from 1 to 14 and SA values remain below 10° expect for PH 14 value, suggesting a good chemical stability of the colorful superhydrophobic coatings to acid droplets, basic droplets and some salt aqueous solutions. Figure 3b shows the variation in water CAs and SAs of the superhydrophobic CuSA2 coating as a function of immersion time in 3.5 wt% NaCl 9


Page 11 of 30

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

Langmuir

aqueous solution. It is clear that the as-prepared coating retains superhydrophobicity because of their water CAs larger than 150°, however, the water SAs increase a little with time evolution in 3.5 wt% NaCl solution. Further increased the immersion time to one month, the SA value on the CuSA2 coating surface increases to 46 ± 3° with the CA value dedreased to 154 ± 1° (Figure 4a and b insets), indicating the surface lost the self-cleaning property. It is well-known that surface wettability is governed by the surface morphology and chemical composition. Using FE-SEM, it was found that the surface morphology of the colorful superhydrophobic coatings did not show any significant change after immersion in 3.5 wt% NaCl solutions even for one month, as shown in Figure 4a and b. Therefore, the wettability variation was supposed to have been caused by the changes of local chemical property, which was proved by XPS analysis (Figure S5, Supporting Information). After immersion in 3.5 wt% NaCl solution for one month, very little Cl element existed on the immersed surface leads to the increase of the SA value. The corrosion resistance of the superhydrophobic surfaces is a key factor determining the possibility of the superhydrophobic surfaces in fundamental research and

practical

applications.30−37

The

corrosion

resistance

of

the

colorful

superhydrophobic coating was tested in 3.5 wt% NaCl aqueous solution by the way of electrochemistry. The superhydrophobic coating on the Al substrate can form a successful barrier against moisture/water diffusion through hydrophobic particles to the underlying Al interface, where corrosion can be initiated. Figure 5 exhibits potentiodynamic polarization curves of pristine aluminum substrate after immersion 10


Langmuir

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

Page 12 of 30

in 3.5 wt% NaCl aqueous solution for 2 h and superhydrophobic CuSA2 coating formed on aluminum substrate after immersion in 3.5 wt% NaCl aqueous solution for 6 h and 30 days at room temperature. Electrochemical parameters like corrosion potential (Ecorr) and corrosion current density (Icorr) for bare Al and CuSA2 coating using the Tafel extrapolation from the potentiodynamic polarization curves are given in Table 2. In a typical polarization curve, a lower corrosion current density usually indicates a lower corrosion rate and a better corrosion resistance.38,39 It should be noted that the Icoor of the superhydrophobic coating on aluminum substrate immersed in 3.5 wt% NaCl corrosive solution for 6 h and for 30 days, decrease by 3 orders and 2 orders than that of bare Al substrate, which means that the superhydrophobic coating provides very effective and long-term protecting the aluminum from corrosion. In addition, the Ecorr of the superhydrophobic coating is more positive than that of the untreated aluminum surface (Figure 5 and Table 2). Thus, we could conclude that the superhydrophobic coating is effective and long-term for improving the corrosion resistance of aluminum surface. Table 2. Ecorr and Icorr for bare Al substrate immersed for 2 h and copper stearate coating immersed for 6 h and 30 days obtained from Tafel measurement in 3.5 wt% NaCl solution. Sample

Ecorr (V) Icorr (A cm-2)

Bare Al

Superhydrophobic coating immersed for 6 h

immersed for 30 days

-0.805

-0.695

-0.656

2.416×10-6

6.019×10-9

3.274×10-8

11


Page 13 of 30

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

Langmuir

EIS is generally recognized as one of effective and revealing method for the corrosion characterization of coated metals.40–42 In the present study, the EIS measurements were performed under open circuit potential in the 3.5 wt% NaCl corrosive solutions with the frequency range from 10 mHz to 100 kHz. Figure 6a depicts the evolution of the impedance spectra of the as-prepared CuSA2 film coated on aluminum surface after immersion in 3.5 wt% NaCl solution for 6 h and 30 days. It can be observed a large semicircle and a tail from the EIS spectra, in which the diameter of the high frequency capacitive loop in the impedance plots represents the polarization resistance of the coating and the low frequency tail is related to the diffusion.32,39 With increase of the immersion time, the loops have little change. As shown in Figure 6a, the superhydrophobic coating has the higher impedance value than that of the interface for bare Al substrate. It is in agreement with the bode plot (impedance modulus |Z| as a function of frequency) in Figure 6b. Although the SA values increase from 4° to 46°after one month immersion, however, there is a little change in the low frequency impedance. One can observe that the impedance modulus |Z| of the resulting superhydrophobic coating immersed for 6 h and 30 days is two orders of magnitude than that of pristine Al substrate. The impedance modulus |Z| of superhydrophobic coating after immersed for 6 h and for 30 days at low frequency maintains a high value and is estimated to be about 1.4×106 Ω cm2, which is about 78 times higher than the resistance of pristine Al substrate. The EIS spectra of the pristine Al surface after immersion in 3.5 wt % NaCl solution for 2 h show one phase maximum at medium frequency, while those of the CuSA2 coated surface after 12


Langmuir

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

immersion in 3.5 wt % NaCl solution for 6 h and 30 days have two phase maxima at relatively low and high frequencies (Figure 6c). The EIS data for other colored coating were also shown (Figure S6-S9, Supporting Information). These results from EIS further demonstrate the as-fabricated colorful superhydrophobic coating provides excellent and long-term anticorrosive properties, which can suppress the contact of aluminum substrate with corrosion solution. The excellent anticorrosion ability of the colored superhydrophobic coatings can be attributed to a synergistic effect of superhydrophobic property based on the stearate salts coatings and air trapped in the porous structure, which maintains a stable air/liquid interface and inhibits erosion of corrosive medium. Spraying is facile and time-efficient approaches that enable the commercial scale production of large-area coatings without the limitation of the specific substrate. The assembly of stearate particles is very fast and leads to homogeneous coatings. The thickness of the colored superhydrophobic coatings gradually increases with the time evolution of sprayed stearate suspension on the substrate. The anticorrosive property of colored superhydrophobic coatings with different thickness nearly kept the same, which could be ascribed to the anti-corrosive property of the top coatings. In addition, the long-term air exposure stability of these superhydrophobic coatings has been investigated. The results shows that these superhydrophobic coatings preserve their superhydrophobic behavior with the CAs larger than 155° and SAs lower than 10° even exposure to air for three months. These observations exhibit that the as-prepared colorful superhydrophobic coatings are rather durable, probably due to the good 13


Page 14 of 30

Page 15 of 30

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

Langmuir

chemical and structural stability of stearate salts. Although the colorful superhydrophobic

coatings

are

mechanical

fragile,

the

destroyed

colorful

superhydrophobic coatings could be repaired by spraying the stearate suspension again on the destroyed coatings. In addition, the low-priced coating repairing materials and simple fabrication method enable the repairable operation at anytime and anywhere without the limitation of the regeneration times. 4. Conclusions In summary, colored hydrophobic stearate particles are synthesized through simple chemical reaction between appropriate inorganic salt and sodium stearate in hot water. Superhydrophobic coatings with water CAs larger than 160° and SAs less than 5° were prepared through a simple one-step spray-coating process by spraying the colored stearate particles ethanol suspensions onto stainless steel substrates, showing uniform and distinguishing colors such as blue, aurantium, purple, cinerous and white respectively. Besides, the colorful superhydrophobic coating possesses excellent chemical stability under both acidic and alkaline harsh circumstances. In addition, the as-prepared coatings still remain superhydrophobicity with the surface morphology nearly unchanged after being immersed in 3.5 wt% NaCl aqueous solution for one month, however, lost the low adhesive property with the SA about 46°. The colored superhydrophobic coatings also exhibits larger impedance and lower corrosion current density than that of untreated aluminum substrate even for one month immersion in 3.5 wt% NaCl corrosive solution. We believed that the convenient and low-cost approach presented here can provide a valid strategy and potential practical 14


Langmuir

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

applications for preparing colorful superhydrophobic coatings on metallic materials with excellent anticorrosive property. Acknowledgements The National Nature Science Foundation of China (Grant No. 21301141), the Nature Science Foundation of Gansu Province, China (145RJYA241), and the Young Teacher Research Foundation of Northwest Normal University (NWNU-LKQN-12-6) are financially supporting this work. Supporting Information FE-SEM image and DLS results of the stearate particles. FT-IR spectra of stearate salts. XPS analysis for CuSA2 particles and CuSA2 coating after immersion in 3.5 wt % NaCl solution for one month. EIS results of other stearate salts coated Al surfaces in 3.5 wt% NaCl solution. This material is available free of charge via the Internet at http://pubs.acs.org. References (1) Feng, L.; Li, S. H.; Li, Y. S.; Li, H. J.; Zhang, L. J.; Zhai, J.; Song, L. Y.; Liu, B. Q.; Jiang, L.; Zhu, D. B. Super-hydrophobic Surfaces: From Nature to Artificial. Adv. Mater. 2002, 14, 1857–1860. (2) Autumn, K.; Liang, Y. A.; Hsieh, S. T.; Zesch, W.; Chan, W. P.; Kenny, T. W.; Fearing, R.; Full, R. J. Adhesive Force of A Single Gecko Foot-Hair. Nature 2000, 405, 681–685. (3) Feng, L.; Zhang, Y. N.; Xi, J. M.; Zhu, Y.; Wang, N.; Xia, F.; Jiang, L. Petal Effect: A Superhydrophobic State with High Adhesive Force. Langmuir 2008, 24, 4114–4119. 15


Page 16 of 30

Page 17 of 30

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

Langmuir

(4) Ragesh, P.; Ganesh, V. A.; Nair, S. V.; Nair, A. S. A Review on Self-Cleaning and Multifunctional Materials. J. Mater. Chem. A 2014, 2, 14773–14797. (5) Yu, S.; Guo, Z.; Liu, W. Biomimetic Transparent and Superhydrophobic Coatings: From Nature and Beyond Nature. Chem. Commun. 2015, 51, 1775–1794. (6) Li, J.; Yan, L.; Ouyang, Q.; Zha, F.; Jing, Z.; Li, X.; Lei, Z. Facile Fabrication of Translucent Superamphiphobic Coating on Paper to Prevent Liquid Pollution. Chem. Eng. J. 2014, 246, 238–243. (7) Darmanin, T.; Guittard, F. Recent Advances in the Potential Applications of Bioinspired Superhydrophobic Materials. J. Mater. Chem. A 2014, 2, 16319–16359. (8) Wang, P.; Zhang, D.; Qiu, R.; Wan, Y.; Wu, J. Green Approach to Fabrication of A Super-hydrophobic Film on Copper and the Consequent Corrosion Resistance. Corros. Sci. 2014, 80, 366–373. (9) Xu, W. J.; Song, J. L.; Lu, Y.; Yu, Z. Y. Rapid Fabrication of Large-Area, Corrosion-Resistant Superhydrophobic Mg Alloy Surfaces. ACS Appl. Mater. Interfaces 2011, 3, 4404–4414. (10) Shubha, H. N.; Venkatesha, T. V.; Vathsala, K.; Pavitra, M. K.; Punith Kumar, M. K. Preparation of Self Assembled Sodium Oleate Monolayer on Mild Steel and Its Corrosion Inhibition Behavior in Saline Water. ACS Appl. Mater. Interfaces 2013, 5, 10738–10744. (11) Li, J.; Yan L.; Li, H.; Li, W.; Zha F.; Lei Z. Underwater Superoleophobic Palygorskite Coated Mesh for the Efficient Oil/Water Separation, J. Mater. Chem. A, 2015, 3, 14696–14702. 16


Langmuir

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

(12) Li, J.; Yan L.; Li, H.; Li, J. P.; Zha F.; Lei Z., A Facile One-step Spray-Coating Process for the Fabrication of Superhydrophobic Attapulgite Coated Mesh Used in Oil/Water Separation, RSC Adv., 2015, 5, 53802–53808. (13) Li, J.; Yan L.; Zhao Y.; Zha F.; Wang, Q.; Lei Z. One-step Fabrication of Robust Fabrics with Both-Faced Superhydrophobicity for Separation and Capture Oil From Water. Phys. Chem. Chem. Phys. 2015, 17, 6451−6457. (14) Li, J.; Jing, Z.; Zha, F.; Yang, Y.; Wang, Q.; Lei, Z. Facile Spray-Coating Process for the Fabrication of Tunable Adhesive Superhydrophobic Surfaces with Heterogeneous Chemical Compositions Used for Selective Transportation of Microdroplets with Different Volumes. ACS Appl. Mater. Interfaces 2014, 6, 8868–8877. (15) Chen, Z.; Du, M.; Lai, H.; Du, Y.; Zhang, N.; Sun, K. Selective Transportation of Microdroplets Assisted by A Superhydrophobic Surface with pH-Responsive Adhesion. Chem. Asian J. 2013, 8, 3200–3206. (16) Li, J.; Jing, Z.; Yang, Y.; Wang, Q.; Lei, Z. From Cassie State to Gecko State: A Facile Hydrothermal Process for the Fabrication of Superhydrophobic Surfaces with Controlled Sliding Angles on Zinc Substrates. Surf. Coat. Technol. 2014, 258, 973–978. (17) Zhang, X.; Shi, F.; Niu, J.; Jiang, Y.; Wang, Z. Superhydrophobic Surfaces: From Structural Control to Functional Application. J. Mater. Chem. 2008, 18, 621–633. (18) Bhushan, B.; Jung, Y. C. Natural and Biomimetic Artificial Surfaces for Superhydrophobicity, Self-Cleaning, Low Adhesion and Drag Reduction. Prog. Mater. 17


Page 18 of 30

Page 19 of 30

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

Langmuir

Sci. 2011, 56, 1–108. (19) Saleema, N.; Sarkar, D. K.; Paynter, R. W.; Chen, X. G. Superhydrophobic Aluminum Alloy Surfaces by A Novel One-Step Process. ACS Appl. Mater. Interfaces 2010, 2, 2500–2502. (20) Li, J.; Jing, Z.; Yang, Y.; Zha, F.; Yan, L.; Lei, Z. Reversible Low Adhesive to High Adhesive Superhydrophobicity Transition on ZnO Nanoparticle Surfaces. Appl. Surf. Sci. 2014, 289, 1–5. (21) Ogihara, H.; Xie, J.; Okagaki, J.; Saji, T. Simple Method for Preparing Superhydrophobic Paper: Spray-Deposited Hydrophobic Silica Nanoparticle Coatings Exhibit High Water-Repellency and Transparency. Langmuir 2012, 28, 4605–4608. (22) Francisco, R.; Hoyos, M.; García, N.; Tiemblo, P. Superhydrophobic and Highly Luminescent Polyfluorene/Silica Hybrid Coatings Deposited onto Glass and Cellulose-Based Substrates. Langmuir 2015, 31, 3718–3726. (23) Rangel, T. C.; Michels, A. F.; Horowitz, F.; Weibel, D. E. Superomniphobic and Easily Repairable Coatings on Copper Substrates Based on Simple Immersion or Spray Processes. Langmuir 2015, 31, 3465–3472. (24) Li, J.; Ling, J.; Yan, L.; Wang, Q.; Zha, F.; Lei, Z. UV/Mask Irradiation and Heat Induced Switching On-Off Water Transportation on Superhydrophobic Carbon Nanotube Surfaces. Surf. Coat. Technol. 2014, 258, 142–145. (25) Manoudis, P. N.; Karapanagiotis, I. Modification of the Wettability of Polymer Surfaces Using Nanoparticles. Prog. Org. Coat. 2014, 77, 331–338. (26) Ishizaki, T.; Sakamoto, M. Facile Formation of Biomimetic Color-Tuned 18


Langmuir

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

Page 20 of 30

Superhydrophobic Magnesium Alloy with Corrosion Resistance. Langmuir 2011, 27, 2375–2381. (27)

Ogihara,

H.;

Okagaki,

J.; Saji,

T.

Facile

Fabrication

of

Colored

Superhydrophobic Coatings by Spraying A Pigment Nanoparticle Suspension. Langmuir 2011, 27, 9069–9072. (28) Soler, R.; Salabert, J.; Sebastián, R. M.; Vallribera, A.; Roma, N.; Ricartand, S.; Molins, E. Highly Hydrophobic Polyfluorinated Azo Dyes Grafted on Surfaces. Chem. Commun. 2011, 47, 2889–2891. (29) Ge, D.; Yang, L.; Wu, G.; Yang, S. Spray Coating of Superhydrophobic and Angle-Independent Coloured Films. Chem. Commun. 2014, 50, 2469–2472. (30) Wang, Z. W.; Li, Q.; She, Z. X.; Chen, F. N.; Li, L. Q. Low-Cost and Large-Scale Fabrication Method for An Environmentally-Friendly Superhydrophobic Coating on Magnesium Alloy. J. Mater. Chem. 2012, 22, 4097–4105. (31) Ishizaki, T.; Masuda, Y.; Sakamoto, M. Corrosion Resistance and Durability of Superhydrophobic Surface Formed on Magnesium Alloy Coated with Nanostructured Cerium Oxide Film and Fluoroalkylsilane Molecules in Corrosive NaCl Aqueous Solution. Langmuir 2011, 27, 4780–4788. (32) Zhao, L.; Liu, Q.; Gao, R.; Wang, J.; Yang, W.; Liu, L. One-Step Method for the Fabrication of Superhydrophobic Surface on Magnesium Alloy and Its Corrosion Protection, Antifouling Performance. Corros. Sci. 2014, 80, 177–183. (33) Rao, A. V.; Latthea, S. S.; Mahadik, S. A.; Kappenstein, C. Mechanically Stable and Corrosion Resistant Superhydrophobic Sol-Gel Coatings on Copper Substrate. 19


Page 21 of 30

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

Langmuir

Appl. Surf. Sci. 2011, 257, 5772–5776. (34) Zang, D.; Zhu, R.; Wu, C.; Yu, X.; Zhang, Y. Fabrication of Stable Superhydrophobic Surface with Improved Anticorrosion Property on Magnesium Alloy. Scripta Mater. 2013, 69, 614–617. (35) Peng, S.; Yang, X.; Tian, D.; Deng, W. Chemically Stable and Mechanically Durable Superamphiphobic Aluminum Surface with a Micro/Nanoscale Binary Structure, ACS Appl. Mater. Interfaces 2014, 6, 15188–15197. (36) Gao, R.; Liu, Q.; Wang, J.; Zhang, X.; Yang, W.; Liu, J.; Liu, L. Fabrication of Fibrous Szaibelyite with Hierarchical Structure Superhydrophobic Coating on AZ31 Magnesium Alloy for Corrosion Protection. Chem. Eng. J. 2014, 241, 352–359. (37) Liu, Q.; Chen, D.; Kang, Z. One-Step Electrodeposition Process to Fabricate Corrosion-Resistant Superhydrophobic Surface on Magnesium Alloy. 2015 ACS Appl. Mater. Interfaces 2015, 7, 1859–1867. (38) Zhang, F.; Zhao, L.; Chen, H.; Xu, S.; Evans, D. G.; Duan, X. Corrosion Resistance of Superhydrophobic Layered Double Hydroxide Films on Aluminum. Angew. Chem. Int. Ed. 2008, 47, 2466–2469. (39) Su, F.; Yao, K. Facile Fabrication of Superhydrophobic Surface with Excellent Mechanical Abrasion and Corrosion Resistance on Copper Substrate by a Novel Method. ACS Appl. Mater. Interfaces 2014, 6, 8762–8770. (40) Zomorodian, A.; Garcia, M. P.; Silva, T. M.; Fernandes, J.C.S.; Fernandes, M. H.; Montemor, M. F. Corrosion Resistance of a Composite Polymeric Coating Applied on Biodegradable AZ31 Magnesium Alloy. Acta Biomater. 2013, 9, 8660–8670. 20


Langmuir

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

(41) She, Z.; Li, Q.; Wang, Z.; Li, L.; Chen, F.; Zhou, J. Novel Method for Controllable Fabrication of A Superhydrophobic CuO Surface on AZ91D Magnesium Alloy. ACS Appl. Mater. Interfaces 2012, 4, 4348–4356. (42) She, Z.; Li, Q.; Wang, Z.; Li, L.; Chen, F.; Zhou, J. Researching the Fabrication of Anticorrosion Superhydrophobic Surface on Magnesium Alloy and Its Mechanical Stability and Durability. Chem. Eng. J. 2013, 228, 415–424.

21


Page 22 of 30

Page 23 of 30

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

Langmuir

Figure Captions Figure 1. Photographs of colored coatings on stainless steel substrates by spraying blue, aurantium, purple, cinerous and white stearate, respectively. Figure 2. FE-SEM images of the as-prepared CuSA2 coatings: (a) low magnification, (b) high magnification and (c) cross-sectional view, respectively. The insets show the water droplet on the coating with (a) CA of 162 ± 1°, (b) a SA of 4 ± 1° and CAH of 3.8°. Figure 3. Variation in the water CAs and SAs of the sample surfaces as a function of (a) pH values of water droplets and (b) immersion time in the 3.5 wt% NaCl aqueous solution. Figure 4. FE-SEM images of the as-prepared CuSA2 coatings immersed in 3.5 wt % NaCl solution for one month: (a) low magnification and (b) high magnification, respectively. The insets show the photographs of a water droplet on the coating with a CA of 154 ± 1° and a SA of 46 ± 3°. Figure 5. Potentiodynamic polarization curves of bare aluminum substrate after immersion in 3.5 wt% NaCl aqueous solution for 2 h and superhydrophobic CuSA2 coating formed on aluminum substrate after immersion in 3.5 wt % NaCl aqueous solution for 6 h and 30 days respectively. Figure 6. EIS results of bare and CuSA2 coated Al surfaces in 3.5 wt% NaCl solution. (a) Nyquist plots, (b) bode |Z| versus frequency plots, and (c) bode–phase angle versus frequency plots.

22


Langmuir

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

The TOC graphic

23


Page 24 of 30

Page 25 of 30

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

Langmuir

Figure 1. Photographs of colored coatings on stainless steel substrates by spraying blue, aurantium, purple, cinerous and white stearate, respectively.


Langmuir

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

Figure 2. FE-SEM images of the as-prepared CuSA2 coatings: (a) low magnification, (b) high magnification and (c) cross-sectional view, respectively. The insets show the water droplet on the coating with (a) CA of 162 ± 1°, (b) a SA of 4 ± 1° and CAH of 3.8°.


Page 26 of 30

Page 27 of 30

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

Langmuir

Figure 3. Variation in the water CAs and SAs of the sample surfaces as a function of (a) pH values of water droplets and (b) immersion time in the 3.5 wt% NaCl aqueous solution.


Langmuir

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

Page 28 of 30

Page 29 of 30

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

Langmuir

Figure 5. Potentiodynamic polarization curves of bare aluminum substrate after immersion in 3.5 wt% NaCl aqueous solution for 2 h and superhydrophobic CuSA2 coating formed on aluminum substrate after immersion in 3.5 wt % NaCl aqueous solution for 6 h and 30 days respectively.


Langmuir

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

Figure 6. EIS results of bare and CuSA2 coated Al surfaces in 3.5 wt% NaCl solution. (a) Nyquist plots, (b) bode |Z| versus frequency plots, and (c) bode–phase angle versus frequency plots.


Page 30 of 30

One-Step Spray-Coating Process for the Fabrication of Colorful

Recommend Documents