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Novel strategy in enhancing stability and corrosion resistance for hydrophobic functional films on copper surfaces
Electrochemistry Communications 11 (2009) 1675–1679
Contents lists available at ScienceDirect
Electrochemistry Communications journal homepage: www.elsevier.com/locate/elecom
Novel strategy in enhancing stability and corrosion resistance for hydrophobic functional films on copper surfaces Shougang Chen *, Yan Chen, Yanhua Lei, Yansheng Yin Institute of Material Science and Engineering, Ocean University of China, Qingdao 266100, PR China
a r t i c l e
i n f o
Article history: Received 9 June 2009 Received in revised form 21 June 2009 Accepted 23 June 2009 Available online 26 June 2009 Keywords: Copper Dopamine Adhesive film Corrosion EIS
a b s t r a c t A rod-like 1-dodecanethiol film assisted with the preferential adhesion of polydopamine was prepared on the non-etching copper surfaces by a simple dip-coating method. The formation and surface structure of the film were characterized by water contact angle measurement, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Once the 1-dodecanethiol film formed on the polydopamine-coated copper surface, the hydrophilic surface changed to hydrophobic. The corrosion behavior of the functional films was evaluated by the electrochemical impedance spectroscopy (EIS). The excellent corrosion resistance property could be ascribed to the compact film structure and good seawater stability for modified copper surface, especially in limiting the infiltration of Cl . Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction The surface modification of bulk material plays important roles in modern chemical, biological, and materials sciences, and in applied science, engineering, and technology [1]. Copper is an important metal in the chemical and microelectronics industries due largely to its high thermal and electrical conductivities and low cost [2–5]. For example, copper alloys are often used in the fabrication of tubes for heat exchangers, electrical power lines for communications, pipelines for domestic and industrial water utilities and copper has become the material of choice in the deposition of highly conductive interconnects on an integrated circuit. A major disadvantage in the use of copper for these applications is that it corrodes easily, especially in aqueous environment containing Cl ions, even trace amounts of Cl [6]. The corrosion resistance of copper devices can be significantly improved by modifying their surfaces with organic molecules and polymers, especially for the superhydrophobic surface coatings. Petrovic et al. reported the corrosion protection of self-assembled alkanethiol monolayer on copper in a sodium acetate solution with a pH of 6 [7]. Azzaroni and Cipollone found that octadecanethiol absorbed on copper surface formed densely packed SAMs, which was found to be effective inhibitors of copper corrosion in a borax buffer containing chloride anions [8]. Tan et al. reported that the maximum efficiency of the SAM of benzenethiols for protection of corrosion of copper in 0.5 M H2SO4 solution was 86.47% * Corresponding author. E-mail address: [email protected] (S. Chen). 1388-2481/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2009.06.021
[9]. Quan et al. studied the corrosion protection ability of the SAMs of shiff-bases on copper surfaces [10]. Abelev et al. explored the efficiency of corrosion resistance in terms of the passivation of copper surface with short-chain alkanoic Acid Potassium Salts [11]. Our previous work [12,13] also successfully fabricated superhydrophobic films by myristic acid on the copper surfaces and attained good corrosion resistance property in seawater. However, in aforementioned work, copper electrodes need to be etched in an acid solution for a period of time, in order to build the linkage between organic films and copper surfaces, but this method to some extent pays the price of sacrificing the mechanical properties of metal surface and undermining the corrosion resistance. Moreover, considering the weak adhesive force of coating layers on the copper surface [7–13], it is an urgent requirement for researchers to fabricate enhanced adhesive force between the coating layer and the metal substrate. Recently, mussel adhesive proteins (MAPs) excreted by marine mussels have attracted much attention because of their ability to form strong adhesive interaction with various substrates in wet environment [14,15], and the dopamine coating layers could be further modified by the strong covalent interaction between thiol- or amine-containing molecules [15,16]. The discovery has stimulated great interest in exploiting catechol to enhance interfacial adhesion of materials [17–19]. Based on above discussions, the aim of this study is to design stable, compact and higher adhesive force functional films assisted with the adhesion of polydopamine on the non-etching copper surfaces by a simple dip-coating method. Meanwhile, the corrosion behavior of hydrophobic 1-dodecanethiol film was also explored.
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S. Chen et al. / Electrochemistry Communications 11 (2009) 1675–1679
2. Experimental section
2.2. Copper surface modification
2.1. Copper surface preparation
Dopamine hydrochloride (2 g/L) was dissolved in 10 mM Tris– HCl (pH 8.5), which is used to prevent the pH of the solution changed, and the pH-induced oxidation changes the solution color until dark brown. Then the cleaned copper substrates were immersed in the alkaline dopamine solution. After 24 h, the substrate was taken out and rinsed with deionized water and dried under the N2 gas flow before storage or treated. For 1-dodecanethiol ad-layer formation,
Copper samples were mechanically polished successively with SiC papers of different grit 400, 800, 1000, 2000 and 0.5 lm diamond paste. These samples were then ultrasonically cleaned with acetone, ethanol and deionized water for 5 min, respectively, and dried with compressed air before coating.
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Fig. 1. X-ray photoelectron spectra of different elements present on the surface of copper covered with dopamine (a) Cu 2p, (b) C 1s, (c) O 1s, (d) N 1s, and (e) N 1s, (f) S 2p of the 1-dodecanethiol film assisted with the adhesive of dopamine.
S. Chen et al. / Electrochemistry Communications 11 (2009) 1675–1679
10 mM of 1-dodecanethiol was dissolved in dichloromethane. Before the formation of 1-dodecanethiol film, the solution should be put the oxygen removed by bubbling with N2, then the polydopamine-coated copper substrate was added. The substrate was taken out after 24 h, and rinsed by ethanol and dried under the N2 blow. 2.3. Surface characterization The morphologies of samples were observed on a field-emission scanning electron microscopy (FE-SEM, JEOL-JSM-6700F) at 5.0 kV, and the corresponding element distributions were determined by an energy dispersive X-ray spectroscopy (EDS). Chemical composition information about the samples was also obtained by X-ray photoelectron spectroscopy (XPS). The measurement was carried out on a PHI-5702 multifunctional spectrometer using Al Ka radiation, and the binding energies were referenced to the C 1s line at 284.8 eV from adventitious carbon. The contact angle was tested with a JC2000C1 CA system at ambient temperature. 2.4. Electrochemical experiments The electrochemical impedance spectroscopy (EIS) was performed by ZAHNER IM6 electrochemical workstation (Germany) at ambient temperature in sterile seawater. The working cell was a standard three-electrode cell having a Pt net as counter electrode, saturated calomel electrode (SCE) as reference electrode and modified copper coupons as working electrode. All measured potentials presented in this paper were referred to SCE. 3. Results and discussion Fig. 1 shows the XPS results of successful self-polymerization of dopamine and 1-dodecanethiol grafting functional films. The
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deconvolution spectra for copper, oxygen, carbon and nitrogen are shown in Fig. 1a–d, respectively. The peaks at 933.4 eV for Cu 2p3/2 and 953.6 eV for Cu 2p1/2 can be attributed to oxidation of copper surface to CuO during polydopamine film formation. The C 1s peaks of 284.7 and 286.1 eV assigned to C–C/C–H, and C–N/C–O, respectively, due to two different carbon environments in the polydopamine. The O 1s peak is observed at 532.1 eV, while the characteristic binding energy of the elemental oxygen is 529.9 eV. The N 1s peak is observed at 400.9 eV, while the characteristic binding energy of the elemental nitrogen is reported as 398.0 eV in the literature [20]. The shift of O 1s and N 1s binding energies indicates that oxygen and nitrogen play vital roles in polymerizing process of dopamine on the copper surface. Fig. 1e and f show the signals of N not detected for copper surface and S not detected for poly(dopamine)-coated copper surface suggest that the 1-dodecanethiol film is indeed formed on copper surface assisted with the adhesion of polydopamine. Fig. 2 shows the surface morphologies and the wettabilities of bare Cu, dopamine modified Cu, and dopamine/1-dodecanethiol modified Cu surfaces. It is evidently found that the polished copper surface is very smooth even at large scale except some nicks (Fig. 2c), and the bare copper surface shows hydrophilic with a water contact angle of about 91°. In Fig. 2a, the dopamine modified copper surface displays a smooth surface morphology without cracks or nicks, and nanometer sized randomly distributed bright granules is formed on the whole substrate. Compared to bare copper, the decrease of contact angle (50°) further indicates that dopamine film is formed on copper substrate, and the EDS analysis (Fig. 2d) of these granules reveals strong N and O signals and the content of C is also obviously increased, which results agree well with the XPS analysis. When 1-dodecanethiol is grafted on the polydopamine-coated copper surface, the surface morphology changed dramatically and many inclined rod-like protrusions
Fig. 2. SEM images of (a) dopamine modified (b) dopamine/1-dodecanethiol modified (c) bare copper surfaces, and the corresponding EDS analysis of (d) dopamine modified and (e) dopamine/1-dodecanethiol modified copper surface. The insets are the contact angle photographs of water droplet covering the surfaces, respectively.
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S. Chen et al. / Electrochemistry Communications 11 (2009) 1675–1679
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Fig. 3. Nyquist diagrams (a) and Bode diagrams (b) for dopamine/1-dodecanethiol modified (Cu + DA + –SH), dopamine modified (Cu + DA) and bare copper (Cu) electrodes immersion in 3.5 wt.% NaCl solution for 1 day. The inset is the amplified diagrams in the higher frequency range.
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modulus of modified copper electrodes is steadily increased, especially for the DA/1-dodecanethiol hydrophobic film, whose Z modulus is increased by three orders of the magnitude to the range of 106 X cm2. Although the contact angle (120°) of the dopamine/1dodecanethiol modified copper surface is smaller than that of previous work [12,13], the interface adhesive force and corrosion resistance property for the hydrophobic film are superior to that of the super-hydrophobic films and other competitors. These experimental phenomena can be easily reproduced. Moreover, the high Z modulus at low frequency indicates that the 1-dodecanethiol film is compact and few porosity and defects (Fig. 2b). Moreover, it cannot be denied that the long-term environmental stability of functional film plays an important role in practical application, so the stability of the dopamine/1-dodecanethiol hydrophobic film was evaluated in seawater (Fig. 4). There is no obvious fluctuation of the contact angles on the surface after storage about 20 days, showing almost no effect of Cl on the surface. The compact film and good seawater stability of modified copper surface explain well the excellent corrosion resistance property, especially in limiting the infiltration of Cl . 4. Conclusion
occurred (Fig. 2b), and the contact angle of the hybrid film increased to 120°. Based on the results of corresponding EDS (Fig. 2e) and above XPS, we think these rod-like protrusions are long alkyl chain of 1-dodecanethiol. In order to explore the corrosion resistance ability of these functional films, the electrochemical technique of EIS was applied. Fig. 3a shows the typical Nyquist impedance plots for the different copper electrodes after 1d immersion in 3.5 wt.% NaCl solution, and the inserted figure is the amplified diagram in the higher frequency range. The impedance spectra of bare copper in 3.5 wt.% NaCl solution contains depressed semicircle whose center lied below the real axis, such behavior is often attributed to the roughness and other inhomogenities of the solid electrode [21,22]. For the modified copper electrodes, the impedance semicircles enlarge markedly but do not change other aspects of the electrode behavior based on the same shapes with the bare copper. It is well known that higher Z modulus at lower frequency displays a better corrosion resistant on the metal substrates [23,24]. Z modulus (Fig. 3b) of the bare copper substrate is in the range of 103 X cm2 at low frequency, suggesting that the bare copper substrate is easily eroded. However, in the same frequency range (Fig. 3b), the Z
The present work shows that stable, compact and higher adhesive force hydrophobic films were prepared with the help of preferential adhesion of polydopamine on the non-etching copper surfaces by a simple dip-coating method. And this functional film keeps the long-term seawater stability and superior corrosion resistance property and can be widely applied in corrosion protection of various engineering materials. Acknowledgments This work was sponsored by National Natural Science Foundation (50702053; 50672090) and Natural Science Foundation of Shandong Province (Y2008B46). References [1] [2] [3] [4] [5]
R. Langer, Science 293 (2001) 58. G.K. Jennings, J.C. Munro, T.H. Yong, P.E. Laibinis, Langmuir 14 (1998) 6130. M. Stolmar, E. Roduner, J. Am. Chem. Soc. 120 (1998) 583. Z.G. Guo, W.M. Liu, B.L. Su, Appl. Phys. Lett. 92 (2008) 063104. Y.H. Lu, H.B. Xu, J. Wang, X.F. Kong, Electrochim. Acta 54 (2009) 3972.
S. Chen et al. / Electrochemistry Communications 11 (2009) 1675–1679 [6] A.K. Geim, S.V. Dubonos, I.V. Grigorieva, K.S. Novoselov, A.A. Zhukov, S.Y. Shapoval, Nat. Mater. 2 (2003) 461. [7] Z. Petrovic, M.M. Hukovic, R. Babic, Prog. Org. Coat. 61 (2008) 1. [8] O. Azzaroni, M. Cipollone, M.E. Vela, R.C. Salvarezza, Langmuir 17 (2007) 1483. [9] Y.S. Tan, M.P. Srinivasan, S.O. Pehkomem, Y.M. Chooi, Corros. Sci. 48 (2006) 840. [10] Z.L. Quan, S.H. Chen, Y. Li, X.G. Cui, Corros. Sci. 44 (2002) 703. [11] E. Abelev, D. Starosvetsky, Y. Ein-Eli, Langmuir 23 (2007) 11281. [12] T. Liu, Y.S. Yin, S.G. Chen, X.T. Chang, S. Cheng, Electrochim. Acta 52 (2007) 3709. [13] T. Liu, S.G. Chen, S. Cheng, J.T. Tian, X.T. Chang, Y.S. Yin, Electrochim. Acta 52 (2007) 8003. [14] E. Loizou, J.T. Weisser, A. Dundigalla, L. Porcar, G. Schmidt, J.J. Wilker, Macromol. Biosci. 6 (2006) 711.
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[15] Z.Y. Xi, Y.Y. Xu, L.P. Zhu, Y. Wang, B.K. Zhu, J. Membrane Sci. 327 (2009) 244. [16] M.J. LaVoie, B.L. Ostaszewski, A. Weihofen, M.G. Scholssmacher, D.J. Selkoe, Nat. Med. 11 (2005) 1214. [17] B.H. Lee, J. Rho, P.B. Messersmith, Adv. Mater. 21 (2009) 431. [18] H. Lee, S.M. Dellatore, W.M. Miller, P.B. Messeramith, Science 318 (2007) 426. [19] M. Yu, T.J. Deming, Macromolecular 31 (1998) 4739. [20] B.V.A. Rao, M.Y. Iqbal, B. Sreedhar, Corros. Sci. 51 (2009) 1441. [21] K.F. Khaled, Mater. Chem. Phys. 112 (2008) 104. [22] I. Thompson, D. Campbell, Corros. Sci. 36 (1994) 187. [23] A.J. Vreugdenhil, V.J. Gelling, M.E. Woods, J.R. Schmelz, B.P. Enderson, Thin Solid Films 517 (2008) 538. [24] M. Qian, A.M. Soutar, X.H. Tan, X.T. Zeng, S.L. Wijesinghe, Thin Solid Films 517 (2009) 5237.
Contents lists available at ScienceDirect
Electrochemistry Communications journal homepage: www.elsevier.com/locate/elecom
Novel strategy in enhancing stability and corrosion resistance for hydrophobic functional films on copper surfaces Shougang Chen *, Yan Chen, Yanhua Lei, Yansheng Yin Institute of Material Science and Engineering, Ocean University of China, Qingdao 266100, PR China
a r t i c l e
i n f o
Article history: Received 9 June 2009 Received in revised form 21 June 2009 Accepted 23 June 2009 Available online 26 June 2009 Keywords: Copper Dopamine Adhesive film Corrosion EIS
a b s t r a c t A rod-like 1-dodecanethiol film assisted with the preferential adhesion of polydopamine was prepared on the non-etching copper surfaces by a simple dip-coating method. The formation and surface structure of the film were characterized by water contact angle measurement, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Once the 1-dodecanethiol film formed on the polydopamine-coated copper surface, the hydrophilic surface changed to hydrophobic. The corrosion behavior of the functional films was evaluated by the electrochemical impedance spectroscopy (EIS). The excellent corrosion resistance property could be ascribed to the compact film structure and good seawater stability for modified copper surface, especially in limiting the infiltration of Cl . Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction The surface modification of bulk material plays important roles in modern chemical, biological, and materials sciences, and in applied science, engineering, and technology [1]. Copper is an important metal in the chemical and microelectronics industries due largely to its high thermal and electrical conductivities and low cost [2–5]. For example, copper alloys are often used in the fabrication of tubes for heat exchangers, electrical power lines for communications, pipelines for domestic and industrial water utilities and copper has become the material of choice in the deposition of highly conductive interconnects on an integrated circuit. A major disadvantage in the use of copper for these applications is that it corrodes easily, especially in aqueous environment containing Cl ions, even trace amounts of Cl [6]. The corrosion resistance of copper devices can be significantly improved by modifying their surfaces with organic molecules and polymers, especially for the superhydrophobic surface coatings. Petrovic et al. reported the corrosion protection of self-assembled alkanethiol monolayer on copper in a sodium acetate solution with a pH of 6 [7]. Azzaroni and Cipollone found that octadecanethiol absorbed on copper surface formed densely packed SAMs, which was found to be effective inhibitors of copper corrosion in a borax buffer containing chloride anions [8]. Tan et al. reported that the maximum efficiency of the SAM of benzenethiols for protection of corrosion of copper in 0.5 M H2SO4 solution was 86.47% * Corresponding author. E-mail address: [email protected] (S. Chen). 1388-2481/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2009.06.021
[9]. Quan et al. studied the corrosion protection ability of the SAMs of shiff-bases on copper surfaces [10]. Abelev et al. explored the efficiency of corrosion resistance in terms of the passivation of copper surface with short-chain alkanoic Acid Potassium Salts [11]. Our previous work [12,13] also successfully fabricated superhydrophobic films by myristic acid on the copper surfaces and attained good corrosion resistance property in seawater. However, in aforementioned work, copper electrodes need to be etched in an acid solution for a period of time, in order to build the linkage between organic films and copper surfaces, but this method to some extent pays the price of sacrificing the mechanical properties of metal surface and undermining the corrosion resistance. Moreover, considering the weak adhesive force of coating layers on the copper surface [7–13], it is an urgent requirement for researchers to fabricate enhanced adhesive force between the coating layer and the metal substrate. Recently, mussel adhesive proteins (MAPs) excreted by marine mussels have attracted much attention because of their ability to form strong adhesive interaction with various substrates in wet environment [14,15], and the dopamine coating layers could be further modified by the strong covalent interaction between thiol- or amine-containing molecules [15,16]. The discovery has stimulated great interest in exploiting catechol to enhance interfacial adhesion of materials [17–19]. Based on above discussions, the aim of this study is to design stable, compact and higher adhesive force functional films assisted with the adhesion of polydopamine on the non-etching copper surfaces by a simple dip-coating method. Meanwhile, the corrosion behavior of hydrophobic 1-dodecanethiol film was also explored.
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S. Chen et al. / Electrochemistry Communications 11 (2009) 1675–1679
2. Experimental section
2.2. Copper surface modification
2.1. Copper surface preparation
Dopamine hydrochloride (2 g/L) was dissolved in 10 mM Tris– HCl (pH 8.5), which is used to prevent the pH of the solution changed, and the pH-induced oxidation changes the solution color until dark brown. Then the cleaned copper substrates were immersed in the alkaline dopamine solution. After 24 h, the substrate was taken out and rinsed with deionized water and dried under the N2 gas flow before storage or treated. For 1-dodecanethiol ad-layer formation,
Copper samples were mechanically polished successively with SiC papers of different grit 400, 800, 1000, 2000 and 0.5 lm diamond paste. These samples were then ultrasonically cleaned with acetone, ethanol and deionized water for 5 min, respectively, and dried with compressed air before coating.
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Fig. 1. X-ray photoelectron spectra of different elements present on the surface of copper covered with dopamine (a) Cu 2p, (b) C 1s, (c) O 1s, (d) N 1s, and (e) N 1s, (f) S 2p of the 1-dodecanethiol film assisted with the adhesive of dopamine.
S. Chen et al. / Electrochemistry Communications 11 (2009) 1675–1679
10 mM of 1-dodecanethiol was dissolved in dichloromethane. Before the formation of 1-dodecanethiol film, the solution should be put the oxygen removed by bubbling with N2, then the polydopamine-coated copper substrate was added. The substrate was taken out after 24 h, and rinsed by ethanol and dried under the N2 blow. 2.3. Surface characterization The morphologies of samples were observed on a field-emission scanning electron microscopy (FE-SEM, JEOL-JSM-6700F) at 5.0 kV, and the corresponding element distributions were determined by an energy dispersive X-ray spectroscopy (EDS). Chemical composition information about the samples was also obtained by X-ray photoelectron spectroscopy (XPS). The measurement was carried out on a PHI-5702 multifunctional spectrometer using Al Ka radiation, and the binding energies were referenced to the C 1s line at 284.8 eV from adventitious carbon. The contact angle was tested with a JC2000C1 CA system at ambient temperature. 2.4. Electrochemical experiments The electrochemical impedance spectroscopy (EIS) was performed by ZAHNER IM6 electrochemical workstation (Germany) at ambient temperature in sterile seawater. The working cell was a standard three-electrode cell having a Pt net as counter electrode, saturated calomel electrode (SCE) as reference electrode and modified copper coupons as working electrode. All measured potentials presented in this paper were referred to SCE. 3. Results and discussion Fig. 1 shows the XPS results of successful self-polymerization of dopamine and 1-dodecanethiol grafting functional films. The
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deconvolution spectra for copper, oxygen, carbon and nitrogen are shown in Fig. 1a–d, respectively. The peaks at 933.4 eV for Cu 2p3/2 and 953.6 eV for Cu 2p1/2 can be attributed to oxidation of copper surface to CuO during polydopamine film formation. The C 1s peaks of 284.7 and 286.1 eV assigned to C–C/C–H, and C–N/C–O, respectively, due to two different carbon environments in the polydopamine. The O 1s peak is observed at 532.1 eV, while the characteristic binding energy of the elemental oxygen is 529.9 eV. The N 1s peak is observed at 400.9 eV, while the characteristic binding energy of the elemental nitrogen is reported as 398.0 eV in the literature [20]. The shift of O 1s and N 1s binding energies indicates that oxygen and nitrogen play vital roles in polymerizing process of dopamine on the copper surface. Fig. 1e and f show the signals of N not detected for copper surface and S not detected for poly(dopamine)-coated copper surface suggest that the 1-dodecanethiol film is indeed formed on copper surface assisted with the adhesion of polydopamine. Fig. 2 shows the surface morphologies and the wettabilities of bare Cu, dopamine modified Cu, and dopamine/1-dodecanethiol modified Cu surfaces. It is evidently found that the polished copper surface is very smooth even at large scale except some nicks (Fig. 2c), and the bare copper surface shows hydrophilic with a water contact angle of about 91°. In Fig. 2a, the dopamine modified copper surface displays a smooth surface morphology without cracks or nicks, and nanometer sized randomly distributed bright granules is formed on the whole substrate. Compared to bare copper, the decrease of contact angle (50°) further indicates that dopamine film is formed on copper substrate, and the EDS analysis (Fig. 2d) of these granules reveals strong N and O signals and the content of C is also obviously increased, which results agree well with the XPS analysis. When 1-dodecanethiol is grafted on the polydopamine-coated copper surface, the surface morphology changed dramatically and many inclined rod-like protrusions
Fig. 2. SEM images of (a) dopamine modified (b) dopamine/1-dodecanethiol modified (c) bare copper surfaces, and the corresponding EDS analysis of (d) dopamine modified and (e) dopamine/1-dodecanethiol modified copper surface. The insets are the contact angle photographs of water droplet covering the surfaces, respectively.
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S. Chen et al. / Electrochemistry Communications 11 (2009) 1675–1679
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Fig. 3. Nyquist diagrams (a) and Bode diagrams (b) for dopamine/1-dodecanethiol modified (Cu + DA + –SH), dopamine modified (Cu + DA) and bare copper (Cu) electrodes immersion in 3.5 wt.% NaCl solution for 1 day. The inset is the amplified diagrams in the higher frequency range.
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Time(days) Fig. 4. The change of contact angle with the time for the dopamine/1-dodecanethiol modified copper surface in seawater.
modulus of modified copper electrodes is steadily increased, especially for the DA/1-dodecanethiol hydrophobic film, whose Z modulus is increased by three orders of the magnitude to the range of 106 X cm2. Although the contact angle (120°) of the dopamine/1dodecanethiol modified copper surface is smaller than that of previous work [12,13], the interface adhesive force and corrosion resistance property for the hydrophobic film are superior to that of the super-hydrophobic films and other competitors. These experimental phenomena can be easily reproduced. Moreover, the high Z modulus at low frequency indicates that the 1-dodecanethiol film is compact and few porosity and defects (Fig. 2b). Moreover, it cannot be denied that the long-term environmental stability of functional film plays an important role in practical application, so the stability of the dopamine/1-dodecanethiol hydrophobic film was evaluated in seawater (Fig. 4). There is no obvious fluctuation of the contact angles on the surface after storage about 20 days, showing almost no effect of Cl on the surface. The compact film and good seawater stability of modified copper surface explain well the excellent corrosion resistance property, especially in limiting the infiltration of Cl . 4. Conclusion
occurred (Fig. 2b), and the contact angle of the hybrid film increased to 120°. Based on the results of corresponding EDS (Fig. 2e) and above XPS, we think these rod-like protrusions are long alkyl chain of 1-dodecanethiol. In order to explore the corrosion resistance ability of these functional films, the electrochemical technique of EIS was applied. Fig. 3a shows the typical Nyquist impedance plots for the different copper electrodes after 1d immersion in 3.5 wt.% NaCl solution, and the inserted figure is the amplified diagram in the higher frequency range. The impedance spectra of bare copper in 3.5 wt.% NaCl solution contains depressed semicircle whose center lied below the real axis, such behavior is often attributed to the roughness and other inhomogenities of the solid electrode [21,22]. For the modified copper electrodes, the impedance semicircles enlarge markedly but do not change other aspects of the electrode behavior based on the same shapes with the bare copper. It is well known that higher Z modulus at lower frequency displays a better corrosion resistant on the metal substrates [23,24]. Z modulus (Fig. 3b) of the bare copper substrate is in the range of 103 X cm2 at low frequency, suggesting that the bare copper substrate is easily eroded. However, in the same frequency range (Fig. 3b), the Z
The present work shows that stable, compact and higher adhesive force hydrophobic films were prepared with the help of preferential adhesion of polydopamine on the non-etching copper surfaces by a simple dip-coating method. And this functional film keeps the long-term seawater stability and superior corrosion resistance property and can be widely applied in corrosion protection of various engineering materials. Acknowledgments This work was sponsored by National Natural Science Foundation (50702053; 50672090) and Natural Science Foundation of Shandong Province (Y2008B46). References [1] [2] [3] [4] [5]
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