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Materials Chemistry and Physics 134 (2012) 657e663

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Materials Chemistry and Physics

journal homepage: www.elsevier .com/locate/matchemphys

Fabrication of CuZn5eZnOeCuO microenano binary superhydrophobic surfacesof CassieeBaxter and Gecko model on zinc substrates

Xiaofeng Shi, Shixiang Lu*, Wenguo Xu*

The Key Laboratory of Cluster Science of Ministry of Education, School of Chemistry, Beijing Institute of Technology, Beijing, China

a r t i c l e i n f o

Article history:Received 4 November 2011Received in revised form18 February 2012Accepted 16 March 2012

Keywords:Thin filmsHeat treatmentSurface propertiesMetals

* Corresponding authors. Tel.: þ86 10 68912667; faE-mail addresses: shixianglu@bit.edu.cn (S. Lu), xu

0254-0584/$ e see front matter � 2012 Elsevier B.V.doi:10.1016/j.matchemphys.2012.03.046

a b s t r a c t

Superhydrophobic surfaces were prepared via immersing the clean perpendicular zinc substrates intoaqueous copper chloride (CuCl2) solution and followed by annealing in dry air. Two Superhydrophobicmodels were obtained by controlling the concentration of CuCl2 aqueous solution. One had a high watercontact angle (CA) of 162 � 2� with a small sliding angle SA of less than 2 � 1�, which was identified withCassieeBaxter model, the other had a high CA of larger than 150� with a high adhesion, which wasidentified with Gecko model. CuZn5eZnOeCuO microenano binary structure leads to super-hydrophobicity of the surface. Wettability and durability of surfaces were investigated and a theoreticalexplanation on superhydrophobic surfaces is presented. Durability test was carried out to study prop-erties of the surface. Formation mechanism of the surface was also explained.

� 2012 Elsevier B.V. All rights reserved.

1. Introduction

Any surface with an apparent water contact angle (CA) largerthan 150� is generally referred as a superhydrophobic surface andwhen the sliding angle (SA) is lower than 5�, the superhydrophobicsurface has the self-cleaning property, otherwise, the super-hydrophobic surface has a high adhesion [1,2]. Superhydrophobicsurfaces with water-repellency, anti-erosion and self-cleaningproperties have attracted a great deal of interest in both academicand industrial research efforts.

Conventionally, superhydrophobic surfaces are governed byboth their chemical composition and surface roughness [3]. Theeffect of roughness on hydrophobicity has been described byWenzel’s model [4] and CassieeBaxter’s model [5]. Variousmethods have been developed to prepare superhydrophobicsurfaces, including electrospinning [6e9], solegel methods[10e15], lithographic methods [16e18], phase separation [19,20],electrochemical deposition [21e23], plasma etching [24e26],chemical vapor deposition [27e30] and liquid-phase deposition[31,32]. However, most of them use organic materials in the prep-aration processes to enhance the surface superhydrophobicity. Themodified surfaces are not stable and restrain some other propertiesof materials due to organic films, such as the heat conduction and

x: þ86 10 68912631.wg60@bit.edu.cn (W. Xu).

All rights reserved.

electric conduction, therefore, researchers try to fabricate super-hydrophobic surfaces without any low-surface-energy modifica-tion, for example, Chen et al. prepared the apparentsuperhydrophobic surface of 3D SnO2 nanoflowers with nano-porous petals using a controlled structure-preserving thermaloxidation process [33], and Li et al. used novel plasma assistedthermal vapor deposition followed by a low pressure oxidation todevelop nanoporous Zn nanobelt and nanowire films performinggood superhydrophobicity [34], and the superhydrophobility wasobserved with the coexistence of the micro- and nanoscaled CuIcrystals prepared by an in-situ etching process in an ethanolsolution via a reaction of copper with I2 [35], Song et al. reportedpreparation of superhydrophobic Au/Cu microenanostructures viaimmersing the copper sheet into HAuCl4 solution [36], and super-hydrophobic nickel nanocones structure and microenano hierar-chical structure were prepared by electrodeposition [37]. Theresulted surfaces exhibited excellent superhydrophobicity withoutany additional modification.

Because metallic materials play an important role in the appli-cations for the modern engineer industry, fabricating a super-hydrophobic surface on them is of great significance. Stablesuperhydrophobic platinum surfaces were fabricated on zincsubstrates in PtCl4 solution without further modification [38]. TheCuZn5eZnO microenano binary structures superhydrophobicsurface was prepared via immersing the zinc substrate intoaqueous copper (II) chloride (CuCl2) solution and followed theannealing under the humid condition [39].

Table 1The table of CAs of the sample 0e8 and the sample 00e80 .

Concentration/mol L�1

Samples

No annealing Annealing

CA CA SA

0 46 � 2� (the sample 0) 111 � 2� (the sample 00) e

0.0025 20 � 2� (the sample 1) 150 � 2� (the sample 10) 180�

0.005 10 � 2� (the sample 2) 153 � 2� (the sample 20) 180�

0.01 4 � 2� (the sample 3) 161 � 2� (the sample 30) 2 � 1�

0.025 21 � 2� (the sample 4) 156 � 2� (the sample 40) 180�

0.05 7 � 2� (the sample 5) 156 � 2� (the sample 50) 180�

0.1 3 � 2� (the sample 6) 155 � 2� (the sample 60) 180�

0.2 5 � 2� (the sample 7) 155 � 2� (the sample 70) 180�

0.3 2 � 2� (the sample 8) 153 � 2� (the sample 80) 180�

0.00 0.05 0.10 0.15 0.20 0.25 0.300

20

40

60

80

100

120

140

160b

Con

tact

ang

le /

º

Concentration / mol⋅L-1

a

Fig. 1. Variation of CAs with different concentration of CuCl2 aqueous solution, (a) thesample 0e8, (b) the sample 00e80 .

X. Shi et al. / Materials Chemistry and Physics 134 (2012) 657e663658

In this work, we investigate the wettability of surfaces on zincsubstrates in different related conditions. The stable super-hydrophobic surfaces with CuZn5eZnOeCuO microenano binarystructures of CassieeBaxter model and Gecko model have beenobtained. The superhydrophobic surfaces were prepared by anneal-ing. Wettability and durability of surfaces were investigated anda theoretical explanationon superhydrophobic surfaces is presented.

2. Experimental methods

2.1. Preparation of superhydrophobic surface

All the chemicals were analytic grade reagents without furtherpurification and from Beijing Chemical Company. Zinc substratewas obtained from Beijing Nonferrous Metal Research Institute.

Briefly, zinc substrates (1.0 cm� 1.0 cm� 0.1 cm, Beijing, 99.9%)were sonicleaned using ethanol, acetone and deionized water,respectively, etched in 1 mol L�1 HCl solution for 5 min to removethe greasy dirt and the zinc oxide layer. The zinc substrates were setperpendicularly in UPVC tube without bottom shown as ourprevious report [39], and then were immersed into CuCl2 aqueoussolution at different concentration (0 mol L�1, 0.0025 mol L�1,0.005mol L�1, 0.01 mol L�1, 0.025 mol L�1, 0.05 mol L�1, 0.1 mol L�1,0.2 mol L�1, 0.3 mol L�1) for an hour at room temperature, thenrinsed with deionized water. Dried in the air, they were placed ina cruciblewith cover, and annealed in the oven at 200 �C for an hour.

In thearticle, samples before annealingare called for short sample0 (0 mol L�1), sample 1 (0.0025 mol L�1), sample 2 (0.005 mol L�1),sample 3 (0.01 mol L�1), sample 4 (0.025 mol L�1), sample 5(0.05 mol L�1), sample 6 (0.1 mol L�1), sample 7 (0.2 mol L�1), andsample 8 (0.3 mol L�1). Similarly, samples after annealing are calledfor short sample 00 (0mol L�1), sample 10 (0.0025mol L�1), sample 20

(0.005mol L�1), sample 30 (0.01 mol L�1), sample 40 (0.025mol L�1),sample 50 (0.05 mol L�1), sample 60 (0.1 mol L�1), sample 70

(0.2 mol L�1), and sample 80 (0.3 mol L�1).

2.2. Characterization

X-ray diffraction (XRD) analyzed on the X’Pert Pro MPD powderdiffractometer, using Cu Ka radiation (40 kV, 40 mA, andl ¼ 0.15418 nm) between 30� and 80� with X’Celerator’s scanningrate of 0.033�/step, 20 s/step; The XPS spectra were obtained ina PHI 5300 X-ray photoelectron spectrometer (Physical Electronics,USA), using 250 W Mg Ka (l ¼ 0.9891 nm) X-ray as the excitationsource, with a constant analyzer energy mode at a chamber pres-sure of 10�7 Pa and wide and narrow scan pass energy of 89.45 eVand 44.75 eV, respectively, at 0.1 eV/step. The C1s line (284.6 eV)was used as the reference with an accuracy of �0.20 eV; Themorphologies were characterized by field-emission scanningelectron microscopy (SEM) which carried out on a field-emission-SEM (JEOL JSM-7500F); Energy-dispersive X-ray spectrometry(EDX) was used to check the composition of the surface.

Static water CA and SA were measured by the sessile-dropmethod with distilled water (8 mL) on optical CA meter (FTÅ 200,Dataphysics Inc., USA) at room temperature. The average CA valueswere obtained by measuring more than five different positions ofone sample. All values of each sample are in a range of �2�, as iserror bars in graph.

3. Results and discussion

3.1. Mechanism of the process

The water CAs and SAs of the sample 0e8 and the sample 00e80

are listed in Table 1. Fig. 1 shows the curves of variation based in

Table 1. Comparing Curve a (the sample 0e8) and Curve b (thesample 00e80), wettability is obviously different before and afterannealing at the same concentration of CuCl2 aqueous solution.Annealing plays an important role in superhydrophobicity ofsurfaces.

It can be seen that the CA of the sample 10e80 are in the rangefrom 150 � 2� to 162 � 2� in Fig. 1b. These results reveal theconcentration of CuCl2 aqueous solution have little or no effect onwettability for the samples, with little difference that is due toexperimental error. That is to say, they are rough enough to performsurface superhydrophobicity. But these surfaces without thesample 30 have high adhesion since the droplets never drop downwhen the substrates turn upside down, which are identified withGecko model [40,41]. By contrast, the water SA of the sample 30 is2 � 1�, which is called CassieeBaxter model theoretically.

Fig. 2 shows SEM images of the samples. The sample 0, 1, 2, 3, 4,5, 6, 7 and 8 are labeled by a, b, c, d, e, f, g, h and i, respectively. Thesample 00, 10, 20, 30, 40, 50, 60, 70 and 80 are labeled by a0, b0, c0, d0, e0, f0,g0, h0 and i0, respectively. The insets are CAs and SAs profiles of waterdroplets on prepared surfaces. It is visible and clear to illustrateFig. 1 and Table 1.

As can be seen, many holes similar to regular hexagon-likehoneycombs are obtained on the zinc substrate by etching in HClsolution in Fig. 2a; A large number of micro-spheres and micro-pillars are formed along the walls of the honeycomb-like cells onthe surfaces of the sample 1e4 and the sample 10e40 in Fig. 2bee;Thin slices assemble on the surfaces of the sample 5e6 and thesample 50e60 in Fig. 2f and g; Thick slices stack to the surfaces of the

Fig. 2. Top-view FESEM images of the samples reacted in CuCl2 solution at different concentration for 1 h before (a, b, c, d, e, f, g, h, i) and after (a0 , b0 , c0 , d0 , e0 , f0 , g0 , h0 , i0) annealing at200 �C for 1 h, aei: the sample 0e8, a0ei0: the sample 00e80 . Insets are CAs and SAs profiles of water droplets (8 mL) on the surface.

X. Shi et al. / Materials Chemistry and Physics 134 (2012) 657e663 659

sample 7e8 and the sample 70e80 in Fig. 2h and i. From thecomparison of SEM images, it is indicated that the surface topog-raphy is related with different concentration of CuCl2 aqueoussolution and is not changed significantly after annealing.

Fig. 3 shows the XRD spectra of the samples. Peaks derived fromthe zinc substrate are so strong that they overtop the line and it isdifficult to be marked in the spectra. The peak marked with “B” issatellite peak of metal zinc. CuZn5 alloys labeled with “7” are

Fig. 3. The XRD spectra of the samples, (a): AeI: the sample 0e8, (b): A0eI0: the sample 00e80 .

X. Shi et al. / Materials Chemistry and Physics 134 (2012) 657e663660

formed in the process of displacement. The peaks of crystalline ZnOare labeled with “A” and the peak of CuO is marked with “-”. Ascan be seen, the peak of ZnO (102) in Fig. 3a (A) is inherent on purezinc substrate; The peak of ZnO (002) is clear in Fig. 3a (B); Peaks ofCuZn5 alloys and ZnO (112) are detected in Fig. 3a (C) e Fig. 3a (E);CuZn5 alloys and ZnO (100), ZnO (002), ZnO (110), ZnO (103) andZnO (112) can be seen clearly in Fig. 3a (F)e Fig. 3a (I). In Fig. 3b, thepeak of ZnO (102) in Fig. 3b (A0) is inherent on pure zinc substrate;Peaks of ZnO (100), ZnO (002), ZnO (110), ZnO (103) and ZnO (112)is clear in Fig. 3b (B0) and Fig. 3b (C0); Peaks of CuZn5 alloys, CuO,ZnO (103) and ZnO (112) are in Fig. 3b (D0) e Fig. 3b (I0). Bycomparison of the samples reacting in CuCl2 aqueous solution at

0 500 1000

Cu

2p

O

1s

Zn

3s

A

Zn

3pZn

3d

B

C /

S

Binding Energy / ev

a

920 940 960 980

Shake-up

peak

c (Cu)

A

B

Shake-up

peak 2p1/2

C /

S

Binding Energy / eV

2p3/2

Fig. 4. The XPS spectra of the samples, (a): The total region, (b): Zn regi

different concentration, ZnO and CuZn5 do not change greatlybefore and after annealing from Fig. 3. In fact, ZnO, CuO and CuZn5are on the surfaces of the samples, but some of them are too smallor amorphous, so the peaks are very slight in the XRD spectra.

All the peaks coincide with that of the standardized PDF card ofzinc (No. 04-0831), CuZn5 (No. 35-1151), CuO (No. 44-0706) andcrystal ZnO (No. 36-1451).

The sample 3 and the sample 30 are taken as examples to furtheridentify the composition with XPS and EDX measurements.

Fig. 4 shows the XPS of the sample 3 labeled with (A) and thesample 30 labeled with (B) in the graphs. Fig. 4a shows the total XPSfor the sample, which reveals that Cu, O and Zn exist on the surfaces

1016 1018 1020 1022 1024 1026 1028 1030 1032 1034 1036

B

(Zn)

A

b

C /

S

Binding Energy / ev

2p3/2

524 526 528 530 532 534 536 538 540 542 544

d

B

(O)

A

C /

S

Binding Energy / eV

1s1/2

on, (c): Cu region, (d): O region: (A) the sample 3 (B) the sample 30 .

X. Shi et al. / Materials Chemistry and Physics 134 (2012) 657e663 661

whether the sample is annealed or not. Fig. 4b shows the XPS of theZn 2p3/2 that the peaks locate at 1021.1 eV in the curve A and1021.3 eV in the curve B which is higher. It reveals that more Zn isoxidized into ZnO when annealing, which is in good agreementwith ZnO (1021.7 eV). Fig. 4c shows the Cu 2p XPS of the samples.The Cu 2p spectrum of the curve A presents a single spin orbital pairwith Cu 2p3/2 and Cu 2p1/2 at 932.2 eV and 951.5 eV. The Cu 2p3/2and Cu 2p1/2 peaks are observed along with their shake-up satel-lites at higher binding energy in both curves as characteristic forCu2þ, suggesting that the signals can be associated with CuO(933.74 eV) species [42e44]. It is in good agreement with theprevious observation in XRD pattern of Fig. 3a (D) and Fig. 3b (D0).After annealing, those of the curve B shift to higher binding energyat 933.0 eV (Cu 2p3/2) and 951.8 eV (Cu 2p1/2), respectively. Theslight shift at high binding energy is indicative of a large chargetransfer from Cu toward the CuO [42e44]. Fig. 4d shows the XPSspectra of the O 1s 1/2 that the peaks located at 530.7 eV in thecurve A and 531.0 eV in the curve B. Higher binding energy on thesample 30 in curve B reveals Cu of low valence transfer toward tothe CuO species when annealing. The slight changes of peak posi-tion can be seen in XPS spectra, which clearly further indicate thatthe compositions of the zinc substrate are changed after annealing,but no new substrates else are generated. More Zn and Cu areoxidizing to ZnO and CuO by annealing.

Fig. 5 shows the EDX spectrum of the sample 30. It reveals thatthe zinc surface reacted with low concentration CuCl2 mainlyconsists of oxygen, copper, and zinc element with a ratio of 40.54%:28.09%: 30.03%.

As shown in Fig. 6a, the water CAs of the resulted surfaceschange with annealing time at 200 �C, which reacted in0.01mol L�1 CuCl2 aqueous solution for an hour. Thewater CAvalueof the zinc substrate annealed for 60 min is highest as shown inFig. 1a. It is indicated that when the annealing time is shorter than60 min, crystalline grain ZnO and CuO generated are not enough toform suitable microenano binary structure; When the annealingtime is longer than 60 min, crystalline grain ZnO and CuO grow somany that they stuff the gap in rough zinc substrate.

Zn Cu

O

Fig. 5. The EDX spectrum

Fig. 6b shows the water CAs on the resulted surfaces variedsignificantly under different annealing temperature for an hour,which reacted in 0.01 mol L�1 CuCl2 aqueous solution for an hour.As can be seen from the graph that the zinc substrate annealed at200 �C is most superhydrophobic. It implies that annealingtemperature lower than 200 �C is too low to form crystalline grainZnO and CuO quickly in an hour to change the surface topography. Itis known that melting points of metal Zn and Cu are 419 �C and1083 �C, respectively, and that of CuZn5 alloy is lower than both ofthem. Once the annealing temperature higher than 200 �C, CuZn5alloy and even the zinc substrate would melt and destroy thestructure of metallic materials.

According to the characteristics of surface topography andcomposition above, the formation mechanism of this specialstructure can be explained by the following discussions: Cu2þ inthe aqueous solution are deoxidize to Cu atom by Zn atom on thezinc substrate. Cu atoms generated in the chemical displacementcome into the crystal zinc lattices or interstices among them toform CuZn5 and the copper zinc alloy, causing crystal zinc defects.Then the chemical displacement preferred occurs at the sites ofthe zinc defects continuously. When the concentration of CuCl2aqueous solution is low, micro-spheres and micro-pillars of CuZn5and the copper zinc alloy are gradually formed on the surface.When the concentration of CuCl2 aqueous solution is high, manyfurcations like the tree branches of CuZn5 and the copper zincalloy are formed. Gradually, they break away from the surfaceeasily because of long reaction time. Since oxygen dissolves in thesolution, it is inevitable that Zn and Cu are oxidized in the processof displacement, but oxidation is weaker than the chemicaldisplacement.

When annealed, the Zn and Cu at active lattices defects on thesurface are oxidized by O2 in air to ZnO and CuO or a mass of crystalZnO germinate, or those generated in displacement grow largergradually on the surfaces. The annealing treatment, an industrialconventional method, changes the properties of metal surfaces. Themain reactions in the system are shown in the following equations:(Scheme 1)

Zn Cu

of the sample 30 .

0 20 40 60 80 100 1200

20

40

60

80

100

120

140

160

Con

tact

ang

le /

°

Heating time / min

a

50 100 150 200 250 30020

40

60

80

100

120

140

160

Con

tact

ang

le /

°

Heating temperature / °C

b

Fig. 6. Annealing time-dependent (a) and annealing temperature-dependent (b) plots of CAs at 0.01 mol L�1 CuCl2 aqueous solution for an hour.

0.8

1.0

X. Shi et al. / Materials Chemistry and Physics 134 (2012) 657e663662

3.2. Theoretical explanation for superhydrophobility

For the sample 30, nano-crystal grains ZnO and CuO growon micro-sized CuZn5 pillars, which form the CassieeBaxtermodel. The coexistence of microenano binary structuresCuZn5eZnOeCuO/zinc is responsible for inducing super-hydrophobic and self-cleaning behavior. Its superhydrophobicity isexplained in terms of the CassieeBaxter equation between thewater CA on a flat surface (q) and a rough surface (q0) (equation (1))[5,6].

cosq0 ¼ f1cosq� f2 (1)

In this equation, f1 and f2 are ratios of solid surface and air incontact with liquid, respectively, and f1 þ f2 ¼ 1. From Fig. 3d0 andFig. 3d, q0 ¼ 162� 2�and q¼ 47� 2�. The resulting values of f1 and f2are about 0.0292 and 0.9708 in calculation, respectively, implyingthat the larger fraction of air among the interspaces on the super-hydrophobic surface. When the water droplet contacts with therough surface, it is the air trapping in the rough structure that propsthe water drop up to prevent the penetration of water droplets intothe cavities, so that the water drop can stand on the surface andslide quickly when the surface slightly tilted. For the sample 10e80

except the sample 30, though their topographies are different, theheight of their microenano binary structures CuZn5eZnOeCuO/zinc is lower than that of the sample 30. When the water dropletis supported on the surface, it penetrates into the structure slightlyand pushes out some air to form a closed hole, which forms theGecko model. So the surfaces show superhydrophobic but havea high adhesion.

0.0

0.2

0.4

0.6

cos

θ

ethanol

3.3. Wettability of different surface tension liquid

Fig. 7 shows that cosines of CA which change with surfacetension of different liquid droplets at 25 �C (gLG/water¼ 72.8 mNm�1,

Zn+Cu2+ Zn2++ Cu

Scheme 1. The main reactions in the formation of superhydrophobic surface.

gLG/glycerol ¼ 63.3 mN m�1, gLG/glycol ¼ 48.4 mN m�1,gLG/ethanol ¼ 22.3 mN m�1) on the superhydrophobic sample 30 withCassieeBaxter model. It is found that cos q of liquids with the samehydroxyl (eOH) is a linear function of gLG. The equation can beobtained bymathematic linear simulation (equation (2)). The liquidsurface tension increases, the CA increases then. Therefore, itmeans that it is thermodynamically favorable for high surfacetension liquid to keep superhydrophobic on the sample 30.

cosq ¼ 1� 0:0271gLGð0 � gLG � 74:1;�1 � cosq � 1Þ (2)

3.4. Durability test

The durability of the superhydrophobic samples (the sample 30,the sample 50, the sample 60 and the sample 70) was tested with CAmeasurement in atmosphere after some days. Fig. 8 shows thecurves of CAs changing in atmosphere after some days. It can beseen that, CAs of the samples all have be decreasing every day. Thesamples with Gecko model are no longer superhydrophobic after90 days. However, the sample 30 with CassieeBaxter model haskept superhydrophobic after exposion in outdoor for a long time. Itis indicated that the superhydrophobic surface of CassieeBaxtermodel is more stable to be laid up a long time in atmospherethan that of Gecko model.

20 30 40 50 60 70 80

-1.0

-0.8

-0.6

-0.4

-0.2

water

glycerol

glycol

γlv / mN⋅m-1

Fig. 7. Cosines of CAs on the surface of the sample 30 changing with surface tension ofdifferent liquid droplets at 25 �C (water, glycerol, glycol, ethanol). The inserts arephotos of the CAs.

0 20 40 60 80 100 120 140 160 180 200 220

115

120

125

130

135

140

145

150

155

160

165

Con

tact

ang

le /

°

Time / Days

0.2 mol⋅L-1

0.01mol⋅L-1

0.1 mol⋅L-10.05 mol⋅L-1

Fig. 8. CAs on the surfaces of the sample 50e70 and the sample 30 changing in atmo-sphere after some days.

0 20 40 60 80

-150

153045607590

105120135150165

c

b

Con

tant

ang

le /

°

Time / Days

a

Fig. 9. CAs changing after some days. (a) The pure zinc substrate in 3.5 wt.% NaClsolution, (b) the sample 30 in 3.5 wt.% NaCl solution, (c) the sample 30 in atmosphere.

X. Shi et al. / Materials Chemistry and Physics 134 (2012) 657e663 663

The durability of the sample 30 was tested in 3.5 wt.% NaClsolutions for several days showed in Fig. 9a. It shows the pure zincsubstrate has been corroded only one day later. And a lot of whiteZn(OH)2 can be seen on its surface in the experiment, which showsthe bad durability in 3.5 wt.% NaCl solution. However, in Fig. 9b, it isfound that the CAs decrease from 162 � 2� to lower than 81 � 2�

after 55 days. The sample 30 with CassieeBaxter model performsbetter durability. But it cannot resist the corrosion in NaCl solutionfor a long time, compared to that in atmosphere from Fig. 9c. So thesuperhydrophobic sample 30 is not suitable to be used in electrolytesolution and is going to be improved in the future research.

4. Conclusions

The zinc substrates were modified by chemical displacement ata perpendicular position and annealed to form microenano binarystructure with CuZn5eZnOeCuO/zinc of CassieeBaxter and Geckomodel, controlled by the concentration of CuCl2 aqueous solution,without further modification of additional low-surface-energycompounds and even without using any organics in the prepara-tion. The annealing treatment plays an important role in

superhydrophobicity of metallic materials. The superhydrophobicsurface of CassieeBaxter model shows better durability in a longtime period in atmosphere than that of Gecko model.

Acknowledgment

We gratefully thank the National Natural Science Foundation ofChina (No. 20933001), National 863 Project of China (No.3170021301004) and the 111 Project of China (No. B 07012) for thework.

References

[1] A. Yildirim, H. Budunoglu, B. Daglar, H. Deniz, M. Bayindir, ACS Appl. Mater.Interfaces 3 (2011) 1804.

[2] M. Miwa, A. Nakajima, A. Fujishima, K. Hashimoto, T. Watanabe, Langmuir 16(2000) 5754.

[3] L. Feng, S. Li, Y. Li, Adv. Mater. 14 (2002) 1857.[4] R.N. Wenzel, Ind. Eng. Chem. 28 (1936) 988.[5] A.B.D. Cassie, S. Baxter, Trans. Faraday Soc. 40 (1944) 546.[6] L. Jiang, Y. Zhao, J. Zhai, Angew. Chem. Int. Ed. 43 (2004) 4338.[7] K. Acatay, E. Simsek, C. Ow-Yang, Y.Z. Menceloglu, Angew. Chem. Int. Ed. 43

(2004) 5210.[8] M. Ma, R.M. Hill, J.L. Lowery, S.V. Fridrikh, G.C. Rutledge, Langmuir 21 (2005)

5549.[9] Y. Zhu, J.C. Zhang, Y.M. Zheng, Z.B. Huang, L. Feng, L. Jiang, Adv. Funct. Mater.

16 (2006) 568.[10] P.M. Barkhudarov, P.B. Shah, E.B. Watkins, D.A. Doshi, C.J. Brinker, J. Majewski,

Corros. Sci. 50 (2008) 897.[11] H. Budunoglu, A. Yildirim, M.O. Guler, M. Bayindir, ACS Appl. Mater. Interfaces

3 (2011) 539.[12] M. Hikita, K. Tanaka, T. Nakamura, T. Kajiyama, A. Takahara, Langmuir 21

(2005) 7299.[13] H.M. Shang, Y. Wang, K. Takahashi, G.Z. Cao, J. Mater. Sci. 40 (2005) 3587.[14] S.S. Latthe, H. Imai, V. Ganesan, A.V. Rao, Micropor. Mesopor. Mater. 130

(2010) 115.[15] N.J. Shirtcliffe, G. McHale, M.I. Newton, C.C. Perry, Langmuir 19 (2003) 5626.[16] D. Öner, T.J. McCarthy, Langmuir 16 (2000) 7777.[17] J. Shieh, F.J. Hou, Y.C. Chen, H.M. Chen, S.P. Yang, C.C. Cheng, H.L. Chen, Adv.

Mater. 22 (2010) 597.[18] B. He, N.A. Patankar, J. Lee, Langmuir 19 (2003) 4999.[19] H.Y. Erbil, A.L. Demirel, Y. Avci, O. Mert, Science 299 (2003) 1377.[20] A. Nakajima, K. Abe, K. Hashimoto, T.Watanabe, Thin Solid Films 376 (2000) 140.[21] N.J. Shirtcliffe, G. McHale, M.I. Newton, C.C. Perry, Langmuir 21 (2005) 937.[22] X. Zhang, F. Shi, X. Yu, H. Liu, Y. Fu, Z.Q. Wang, L. Jiang, X.Y. Li, J. Am. Chem. Soc.

126 (2004) 3064.[23] F. Shi, Z.Q. Wang, X. Zhang, Adv. Mater. 17 (2005) 1005.[24] W. Chen, A. Fadeev, M. Heich, Langmuir 15 (1999) 3395.[25] K. Tsougeni, N. Vourdas, A. Tserepi, E. Gogolides, C. Cardinaud, Langmuir 25

(2009) 11748.[26] D.O.H. Teare, C.G. Spanos, P. Ridley, E.J. Kinmond, V. Roucoules, J.P.S. Badyal,

S.A. Brewer, S. Coulson, C. Willis, Chem. Mater. 14 (2002) 4566.[27] S. Harasek, H.D. Wanzenboeck, B. Basnar, J. Smoliner, J. Brenner, H. Stoeri,

E. Gornik, E. Bertagnolli, Thin Solid Films 414 (2002) 199.[28] K.K.S. Lau, J. Bico, K.B.K. Teo, M. Chhowalla, G.A.J. Amaratunga, W.I. Milne,

G.H. McKinley, K.K. Gleason, Nano Lett. 3 (2003) 1701.[29] Y.Y. Wu, M. Bekke, Y. Inoue, H. Sugimura, H. Kitaguchi, C.S. Liu, O. Takai, Thin

Solid Films 457 (2004) 122.[30] L. Huang, S.P. Lau, H.Y. Yang, E.S.P. Leong, S.F. Yu, S. Prawer, J. Phys. Chem. B

109 (2005) 7746.[31] J.L. Campbell,M.Breedon,K. Latham,K.Kalantar-zadeh, Langmuir24 (2008)5091.[32] S.L. Gras, T. Mahmud, G. Rosengarten, A. Mitchell, K. Kalantar-zadeh, Chem-

PhysChem. 8 (2007) 2036.[33] A.C. Chen, X.S. Peng, K. Koczkur, B. Miller, Chem. Commun. 17 (2004) 1964.[34] G. Li, B. Wang, Y. Liu, T. Tan, X.M. Song, H. Yan, Appl. Surf. Sci. 255 (2008) 3112.[35] L. Xin, M. Wan, Cryst. Growth Des 6 (2006) 2661.[36] W. Song, J. Zhang, Y. Xie, Q. Cong, B. Zhao, J. Colloid Interface Sci. 329 (2009) 208.[37] T. Hang, A.M. Hu, H.Q. Ling, M. Li, D.L. Mao, Appl. Surf. Sci. 256 (2010) 2400.[38] T. Ning, W.G. Xu, S.X. Lu, J. Colloid Interface Sci. 361 (2011) 388.[39] W.G. Xu, X.F. Shi, S.X. Lu, Mater. Chem. Phys. 129 (2011) 1042.[40] M.H. Jin, X.J. Feng, L. Feng, T.L. Sun, J. Zhai, T.J. Li, L. Jiang, Superhydrophobic

aligned polystyrene nanotube films with high adhesive force, Adv. Mater. 17(2005) 1977e1981.

[41] X. Hong, X.F. Gao, L. Jiang, Application of superhydrophobic surface with highadhesive force in no lost transport of superparamagnetic microdroplet, J. Am.Chem. Soc. 129 (2007) 1478e1479.

[42] B. Xu, L. Dong, Y. Chen, J. Chem. Soc. Faraday Trans. 94 (1988) 1905.[43] G. Córdoba, M. Viniegra, J.L.G. Fierro, J. Padilla, R. Arroyo, J. Solid State Chem.

138 (1998) 1.[44] J.P. Espinós, J. Morales, A. Barranco, A. Caballero, J.P. Holgado, A.R. González-

Elipe, J. Phys. Chem. B 106 (2002) 6921.