ECS Electrochemistry Letters, 1 (4) D21-D23 (2012) D212162-8726/2012/1(4)/D21/3/$28.00 © The Electrochemical Society

Simultaneous Fabrication of Superhydrophobic Coatingson Cathodic and Anodic Copper Surfaces with Micro/Nano-StructuresZhi Chen,a,z Limei Hao,b and Changle Chena

aDepartment of Applied Physics, Northwestern Polytechnical University, Xi′an 710129, ChinabDepartment of Applied Physics, Xi′an University of Science & Technology, Xi′an 710054, China

In this letter, we presented a novel one-step electrodeposition method to prepare two superhydrophobic coatings, and it cansimultaneously fabricate two different superhydrophobic coatings on cathodic and anodic copper surfaces, respectively. The as-fabricated cathodic superhydrophobic coatings need only 15 sec, and the anodic superhydrophobic coatings need 5 min, which isshorter than that in the reported literature. The cooperation of hierarchical structures and low surface energy plays an important rolein the formation of superhydrophobicity. Furthermore, both of the coatings are bulk materials, and have a good extensive applicationprospect.© 2012 The Electrochemical Society. [DOI: 10.1149/2.001205eel] All rights reserved.

Manuscript submitted May 7, 2012; revised manuscript received July 16, 2012. Published August 24, 2012.

Superhydrophobic surfaces with water contact angle larger than150◦ have attracted significant attention due to their many practi-cal applications in diverse areas.1,2 Many researchers have fabricatedartificial superhydrophobic surfaces by mimicking the surface of lo-tus leaves.3 All of methods emphasize the coexistence of surfaceroughness and the low surface energy to obtain superhydrophobic-ity. Therefore, if both of surface roughness and low surface energywere achieved in one-step method, the conventional two steps proce-dure could be simplified, and the fabrication process would largelybe shortened.4 A copper carboxylate superhydrophobic film was pre-pared with one-step solution-immersion process.5 However, it is time-consuming from ten hours to several days. Furthermore, electrodepo-sition has emerged as a competitive technique for the advantages overother techniques: easy control of the thickness of the surface; simplic-ity; inexpensive equipment, and the possibility of making large-areasurface.6,7 Recently, this type of superhydrophobic surface was alsoconstructed by a time-saving electrodeposition method.8,9 However,there is only limited published literature concerning a rapid one-stepprocess to fabricate anodic9 or cathodic superhydrophobic surfaces10

by electrodeposition method, but no published literature about si-multaneous fabrication of two anodic and cathodic superhydrophobiccoatings.

In the letter, ferric chloride (FeCl3 · 6H2O) was added to a uniformsolution of myristic acid and ethanol to accelerate the reaction process;such a system presents a novel and rapid electrodeposition method forsimultaneously constructing environmentally stable superhydropho-bic coatings on cathodic and anodic copper surfaces, respectively.

Experimental

All chemical reagents used in the experiment were of analyticalgrade and used without further purification. The electrolyte is a uni-form 150 mL solution of ferric chloride, myristic acid, and ethanol.Two clean copper plates were used as the cathode and anode in anelectrolytic cell with a direct current (DC) voltage of 30 V and a dis-tance of 2 cm. After an electrolysis time of 0.1 to 90 min, the workingelectrodes were rinsed thoroughly with distilled water and ethanoland then dried with an air conditioner. The samples obtained werethen characterized by field-emission scanning electron microscopy(FE-SEM, JSM-6390A), and the crystalline phases were determinedby X-ray diffraction (XRD, D/max2400) with monochromatic CuKα radiation. Infrared transmission spectrum was recorded at roomtemperature on a Fourier transform infrared spectrophotometer (FTIR,BRUKER-Tensor27), and contact angle analyzes were performed withan optical Charge-coupled Device (CCD; CNB-GP300 CGG1) at anambient temperature. The average contact angle value was determined

zE-mail: c2002z@nwpu.edu.cn

by measuring the sample at five different positions. Water droplets ofabout 5 μL were dropped onto the superhydrophobic coatings from adistance of 0.2 cm by a vibrating burette.

Results and Discussion

Figs. 1a and 1b show SEM images of the as-prepared cathodicsurfaces after application of a DC voltage of 30V DC to a solu-tion of 0.025M ferric chloride and 0.2M myristic acid electrolyte for10 min. Fig. 1a shows many cactus-like particles on the cathodic sur-face after an electrodeposition process with diameters ranging from1 μm to 3 μm. A high-magnification SEM image the cathodic surface(Fig. 1b) shows that the cactus-like morphology includes hierarchi-cal micro/nano- structures with each cactus composed of one sphereand many thin nanosheets, which increase the surface roughness. Asshown in the inset in Fig. 1b, a water droplet on the coatings indicateshigh superhydrophobicity on the cathodic surface.

The structure and composition of the cathodic coatings were de-termined by XRD and FTIR analysis. Fig. 1c shows the XRD spectraof the cathodic coatings at room temperature. Three equally distancedpeaks marked with “#” appear in the range of 1.5◦ to 10◦, indicating thepresence of lamellar structures. FTIR analysis was used to determinethe composition of lamellar structures observed in the small-angleregion of the XRD patterns obtained. As shown in Fig. 1d, the sym-metric –CH stretching absorption band at 2920 cm−1 and asymmetric–CH stretching absorption band at 2853 cm−1 indicate the presenceof a long-chain alkyl group11 on the cathodic coatings. Two new ab-sorption bands at 1455 and 1578 cm−1 are assigned to symmetricand asymmetric COO– stretching vibrations, respectively. Thus, thelamellar structures on the cathodic coatings appear to be composed offerric myristate (Fe[CH3(CH2)12COO]3). In short, the appearance ofthe ferric myristate confirms the presence of methylated components(CH3 and CH2) with low surface energy on the cathodic surface. Bub-bles were also observed near the cathode during the reaction process,probably due to the formation of hydrogen.12

Fig. 2a depicts the relationship between the contact angle andelectrodeposition time. Short durations of electrodeposition (0.25 min)are sufficient to render superhydrophobicity on the cathodic surface.As the deposition time increases, the contact angle increases. Whenthe deposition time is 1 min, the contact angle is 160◦. When the timeis extended to 10 min, the contact angle increases to 165◦ and therolling angle becomes less than 2◦. Further increasing the depositiontime from 10 min to 90 min does not result in further improvement inthe contact angle.

When the powder scraped from the cathodic surface with a knifewas adhered to a piece of self-adhesive tape, the tape also exhib-ited excellent superhydrophobic properties, as seen from the inset inFig. 2a. Thus, the coating is confirmed to be a bulk material withextensive potential for application in large-scale production.

) unless CC License in place (see abstract).  ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 164.41.102.240Downloaded on 2014-05-17 to IP

D22 ECS Electrochemistry Letters, 1 (4) D21-D23 (2012)

Figure 1. SEM images of cathodic coatings after 10 min of exposure to a solution of 0.025M ferric chloride and 0.2M myristic acid electrolyte at 30 V: (a) 3000×;(b) 10000×; (c) The XRD spectrum of the coatings; (d) The FTIR spectrum of the coatings.

Aside from the cathodic coatings, analysis of the characteristicsof the corresponding anodic coatings was also performed after 2 dof exposure to the ambient room temperature under air conditioning.Fig. 2b shows the relationship between the contact angle and elec-trodeposition time. When the deposition time is 5 min, the anodicsurface exhibits a contact angle of 152◦ and a rolling angle of lessthan 5◦. Increasing the deposition time improves the superhydropho-bic performance of the anodic coatings; such that the contact angle canis 155◦ after 10 min of deposition. However, when the time is furtherextended, the contact angle begins to decrease. The contact angle sig-nificantly decreases after the deposition time more than 30 min, likelybecause the coatings become too thick and weakly-adhered powderdesquamated from the anodic surface. When these desquamated coat-ings were collected from the electrolytic cell, washed with water andethanol, dried on a piece of paper, and then exposed to air for 1 d,superhydrophobic properties were still observed. The inset in Fig. 2bshows water droplets on the sheet of paper, which suggests that theanodic coatings are also composed of bulk materials.

Figs. 3a and 3b show SEM images of the anodic coatings for10 min. Anodic coatings were also composed of many micro/nano-particles. Fig. 3c shows three obvious peaks marked with “#”, indicat-ing the presence of a small amount of myristate salt in the coatings.The diffraction peaks13 marked with “*” are assigned to paratacamite(Cu2(OH)3Cl), consistent with JPDF Card No. 01-0793. The peaksmarked with “∇” also match the JPDF card of CuCl (Card No. 19-0389). Fig. 3d depicts the FTIR spectrum of the anodic coatings, whereabsorption peaks of 3449, 3333, 986, 921, 848, 591, 513 and 456 cm−1

are assigned to Cu2(OH)3Cl 14 and the peaks of 2915, 2849, 1443 and1585 cm−1 are mainly attributed to the vibration peaks of coppermyristate.15 From the FTIR and XRD analyzes, we can concludethat the anodic coatings are composed of Cu[CH3(CH2)12COO]2,Cu2(OH)3Cl, and CuCl. The cooperation of micro/nano- particlesand copper myristate with the low surface energy together realizes thesuperhydrophobicity of anodic surface.

It is seen from Fig. 2 that the maximum contact angle on ca-thodic coatings is 165◦, while that of the smooth copper surface with

Figure 2. Changes in the water contact angle of the coatings with increasing electrolysis time: (a) Cathodic surface and (b) Anodic surface.

) unless CC License in place (see abstract).  ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 164.41.102.240Downloaded on 2014-05-17 to IP

ECS Electrochemistry Letters, 1 (4) D21-D23 (2012) D23

Figure 3. SEM images of anodic coatings after 10 min of exposure to a solution of 0.025M ferric chloride and 0.2M myristic acid electrolyte at 30 V: (a) 500×;(b) 3000×; (c) The XRD spectrum; (d) The FTIR spectrum.

myristic acid is about 109◦. When these angles are introduced intoC-B equation,16 it is estimated that the air interfacial area is 0.949 andmicro/nano- structures area is only 0.051. Similarly, the air interfa-cial area on anodic coatings is 0.861. Thus, two deposited electrodesurfaces with micro/nano- structures and low surface energy pos-sess the high air area and then show the excellent superhydrophobicproperty.

Conclusion

Two excellent superhydrophobic coatings were simultaneouslyfabricated via a rapid, simple, and one-step electrodeposition pro-cess on cathodic and anodic copper surfaces from an electrolytesolution including ferric chloride, myristic acid, and ethanol, re-spectively. As-prepared cathodic coatings for electrodeposited for0.25 min possessed superhydrophobic properties. When electrode-position time is increased to 10 min, the contact angle reaches 165◦.Corresponding anodic coatings electrodeposited for 10 min also fea-ture superhydrophobicity and contact angle of 155◦. Cathodic coat-ings consist of Fe [CH3(CH2)12COO]3 and anodic coatings consistof Cu[CH3(CH2)12COO]2, Cu2(OH)3Cl, and CuCl. This method issimple, requires a short preparation time, yields the bulk material-type anodic and cathodic coatings, and uses inexpensive chemicals.Therefore, the method is economical and suitable for large-scaleproduction.

Acknowledgments

This work was supported by the National Natural Science Founda-tion of China (No.11102164), the Scientific Research Program Fundedby Shaanxi Provincial Education Department (No. 12JK0966) and theFundamental Research Fund of Northwestern Polytechnical Univer-sity, China (Nos. JC201267, JC200919).

References

1. Y. Y. Yan, N. Gao, and W. Barthlott, Adv. Colloid Interface Sci., 169, 80 (2011).2. K. S. Liu and L. Jiang, Nano Today, 6, 155 (2011).3. W. Barthlott and C. Neinhuis, Planta, 202, 1 (1997).4. N. Saleema, D. K. Sarkar, R. W. Paynter, and X. G. Chen, ACS Appl. Mater. Inter-

faces, 2, 2500 (2010).5. S. Wang, L. Feng, and L. Jiang, Adv. Mater., 18, 767 (2006).6. I. Zhitomirsky, Adv. Colloid Interface Sci., 97, 279 (2002).7. L. Wang, S. J. Guo, X. G. Hu, and S. J. Dong, Electrochem. Commun., 10, 95 (2008).8. J. M. Xi, L. Feng, and L. Jiang, Appl. Phys. Lett., 92, 053102 (2008).9. Y. Huang, D. K. Sarkar, and X. G. Chen, Mater. Lett., 64, 2722 (2010).

10. Z. Chen, L. M. Hao, A. Q. Chen, Q. J. Song, and C. L. Chen, Electrochim. Acta, 59,168 (2012).

11. J. M. Xi, L. Feng, and L. Jiang, Appl. Phys. Lett., 92, 053102 (2008).12. W. L. Tsai, P. C. Hsu, Y. H. Wu, C. H. Chen, L. W. Chang, J. H. Je, H. M. Lin,

A. Groso, and G. Margartondo, Nature, 417, 139 (2002).13. A. R. Mendoza, F. Corvo, A. Gomez, and J. Gomez, Corros. Sci., 46, 1189 (2004).14. A. Lluveras, S. Boularand, A. Andreotti, and M. Vendrell-Saz, Appl. Phys. A, 99, 363

(2010).15. S. T. Wang, L. Feng, and L. Jiang, Adv. Mater., 18, 767 (2006).16. A. B. D. Cassie and S. Baxter, Trans. Faraday Soc, 546, 40 (1944).

) unless CC License in place (see abstract).  ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 164.41.102.240Downloaded on 2014-05-17 to IP