- Email: [email protected]
Facile electrodeposition of superhydrophobic and oil-repellent thick layers on steel substrate
Materials Letters 184 (2016) 243–247
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Facile electrodeposition of superhydrophobic and oil-repellent thick layers on steel substrate Barbora Pijáková n, Miloš Klíma, Milan Alberti, Vilma Buršíková Department of Physical Electronics, Masaryk University, 267/2 Kotlářská, Brno CZ-61137, Czech Republic
art ic l e i nf o
a b s t r a c t
Article history: Received 25 January 2016 Received in revised form 20 June 2016 Accepted 13 August 2016 Available online 15 August 2016
The aim of this work is to produce liquid-repellent surface on stainless steel via simple electrodeposition. For this purpose, myristic acid, stearic acid ethanol solution and perfluorooctanoic acid aqueous solution were used. Resulting contact angles and surface energy values were studied. Superhydrophobic and superoleophobic behavior of samples prepared using perfluorooctanoic acid electrolyte were performed by contact angle 159° for deionized water, 153° for olive oil and low surface energy 0.60 mJ/m2. Relation between the non-wettable behavior of samples, surface structure, chemical composition and mechanical properties were observed by SEM with EDX analysis, FTIR spectroscopy and tribological measurement, giving the preference to fluorinated precursor and low voltage electrodeposition. & 2016 Elsevier B.V. All rights reserved.
Keywords: Electrodeposition Superhydrophobicity Superoleophobicity Functional surface Perfluorooctanoic acid
1. Introduction A repellency of the surfaces for various liquids is the point of the interest for many research teams [1,2]. Characterization of non-wettable behavior is realized by measuring the contact angle (CA) values of liquids on the surface [3]. As the result of the theoretical aspects introducing the Young's equation, Wenzel and Cassie-Baxter wetting models [4–6], the roles of surface energy, surface morphology and surface tension are crucial. For perspective application, there are two necessary steps to reach the repellency, namely creation of an appropriate morphology and the modification of surface energy by suitable chemical composition [7,8]. The bioinspiration lead to mimicking of natural morphology and production of artificial surfaces in laboratory conditions [9– 11]. An application of liquid-repellent products introduces the large quantity of possible substrates for modification such as textiles [12], wood [13], plastics [14,15], paper [16,17] or glass [18,19]. Important substrates for industry are metals. The hybrid surface modification consists of enhancing the surface roughness with inorganic nanoparticles or chemical etching and additive modification of nanoparticles by organic precursors such as fluorinated organic compounds [20–22]. Many research teams present the preparation of superhydrophobic surface on metals such as aluminum [1,23,24], copper [25,26] or iron [27] by long-time n
Corresponding author. E-mail address: [email protected] (B. Pijáková).
http://dx.doi.org/10.1016/j.matlet.2016.08.078 0167-577X/& 2016 Elsevier B.V. All rights reserved.
immersions of substrate with modified structure in stearic acid (SA), myristic acid (MA) [28,29] with analogue results given by replacing the precursors with perfluorooctanoic acid (PFOA) [30], providing water and oil repellency. Two-step methods consisting of the microstructure formation and hydrophobization were replaced by controlled electrolysis with ethanol solution of SA or MA as electrolytes [31,32–34]. This method is time-saving, simple and effective for metal substrate modification. However, the products exhibit no repellency for low surface tension liquids. Herein, we report simple time-saving deposition method of liquid-repellent layers on the stainless steel. Furthermore, by introducing of PFOA in electrolyte, water and oil repellent coatings are formed, prioritizing PFOA before non-fluorinated organic acids requiring addition of inorganic salt. Substitution of ethanol with water in electrolyte containing PFOA could help to solve the problem of acid persistence in water [35,36] by recycling the contaminated fraction of water. Deposited layers can be applied to enhance the corrosion resistance or to introduce functional properties such anti-icing and self-cleaning.
2. Experimental 2.1. Materials and methods 2.1.1. Materials PFOA (Alfa Aesar, 95%), MA (Alfa Aesar, 98%), lanthanum(III) chloride heptahydrate (LaCl3 7H2O, Alfa Aesar, 99%), SA (Lachema,
244
B. Pijáková et al. / Materials Letters 184 (2016) 243–247
Table 1 CA values for testing liquids and calculated surface free energy. Liquid CA [deg] Sample
Distilled water
Glycerol
Ethylene glycol
Diiodomethane
Formamide
1-bromonaphthalene
Surface free energy [mJ/m2]
sMA sSA sPFOA
1567 2 151 73 1597 2
149 7 5 148 7 8 1547 3
148 74 1397 8 1527 2
106 7 11 122 77 1417 3
1507 3 1427 12 1417 4
637 28 64 7 19 1447 5
16.10 11.40 0.60
Fig. 1. SEM micrographs of surface structure (magnification 10 kx), inset of image detail (magnification 50 kx) and water droplet with stated WCA for sMA, sSA and sPFOA samples.
95%), potassium bromide (KBr, Sigma Aldrich, Z99%), ethanol (Sigma-Aldrich, 95%), glycerol (Sigma-Aldrich, Z99%), 1-bromonaphthalene, ethyleneglycol (Sigma-Aldrich, Z99.5%), diiodomethane (Sigma-Aldrich, 99%), formamide (Sigma-Aldrich, Z99.5%) and deionized water (conductivity 18.18 mS/cm at 13 °C; prepared at Masaryk university using RO 1-1CC unit by MEMSEP Ltd.) were used for experiments. 2.1.2. Surface characterization CA and surface energy values, averaged from ten measurements, were obtained by Surface Energy Evaluation (see) System device with eponymous software (AdveX Instruments) for 2.5 μl droplets. The surface energy was determined using the six-liquid Owens-Wendt regression model. Norm-referenced neutral salt spray (NSS) corrosion tests were realized for 1000 h according to CSN EN ISO 9227 NSS to observe possible corrosion product formation. Macroscopic topography and surface roughness was characterized by confocal microscope Olympus LEXT OLS4000 operating with LEXT software. For microstructure observation, SEM Tescan MIRA3 using secondary electron (SE) detector was employed. Each sample was coated by 19 nm of gold in order to prevent surface charging. The film thickness was measured using DektakXT (Bruker) mechanical profilometer. The mechanical properties of the films were studied using TI950 (Hysitron) and Fischerscope H100 nanoindenters. The scratch resistance and film adhesion were studied by means of Revetest Xpress plus scratch tester (Anton Paar) equipped with a Rockwell type diamond indenter with a radius of 200 mm. The load was increased at a constant rate 16 N/min, while the scratch length was 16 mm. Occurrence of chemical elements from precursors was stated in wt% by SEM-EDX mapping of the 25 mm2 area. FTIR spectrometer Bruker VERTEX 80v equipped with attenuated total reflectance (ATR) plate measured reflectance spectra of samples on steel substrate and transmittance spectra of KBr pellets containing pure precursors (concentration up to 1%). 2.2. Electrodeposition Stainless steel plates 20 70 1.5 mm in size were cleaned in
ethanol, ethanol/deionized water, deionized water ultrasonic bath, each for 15 min and dried with the airflow. Electrolytes with concentration of 0.1 M MA and 0.038 M of LaCl3 7H2O in ethanol, 0.05 M SA with 0.038 M LaCl3 7H2O in ethanol and 0.045 M PFOA in deionized water were prepared two hours prior the deposition. The distance between the electrodes was two centimeters. Using DC power supply DF3010 (Wentronic GmbH), working conditions were set to 30 V for 10 min for MA electrolyte according to [37], 15 V for 10 min for SA and 5 V for 20 min for PFOA solution. Optimal working conditions for SA and PFOA electrolytes were optimized in dependence on water CA (WCA) (see Table S1 Supplementary material). After the deposition termination, samples were retained in a fume hood until dried.
3. Results and discussion 3.1. Contact angle and surface energy measurement WCA values were stated 156 72°, 1517 3° and 159 72° for prepared samples sMA, sSA and sPFOA respectively, exhibiting superhydrophobic behavior. However, the CA for olive oil (OCA) with surface tension of E32 mN/m was impossible to state for sMA and sSA due to their oleophilicity. OCA for sPFOA was stated in a range of 15373° exhibiting superoleophobic behavior. The high liquid CAs ensure the perspective usage of PFOA products. The Table 1 contains the CA values for liquids and surface energies, that were stated 16.10 mJ/m2, 11.40 mJ/m2 and 0.60 mJ/m2 for sMA, sSA and sPFOA, respectively. Low deviations for sPFOA CA values predict eligible material uniformity. The Meng et al. [38] referred that surface energy exceeding the one-quarter of the liquid surface tension result in wettable behavior (CA o90°). This fact fitted to surface energies of sMA, sSA and sPFOA in relation to OCA. The significant change of sPFOA surface energy corresponded to the presence of fluorine. Reproducibility of layers was considerable, providing low deviations for numerous WCAs measurement (see, Table S2).
B. Pijáková et al. / Materials Letters 184 (2016) 243–247
245
Fig. 2. IR spectra of deposited samples sMA, sSA, sPFOA and unmodified precursors MA, SA, PFOA with marked bands of characteristic groups vibrations.
3.2. Corrosion testing After 1000 h in NSS chamber, no evidence of corrosion product formation was observed for sMA, sSA an sPFOA. Thus, the deposition and produced layers do not support or initiate corrosion processes. 3.3. Structure observation Surface thickness was 2376 mm, 137 4 mm, 12 72 mm, whereas roughness was 26 mm, 10 mm and 8 mm for sMA, sSA and
sPFOA, respectively (see Fig. S1 in Supplementary material). The roughness was related to applied voltage, in terms of enhancing surface formation growth and gas bubbles production with increasing voltage. For sMA, visible raising bubbles paths were created. In comparison to sSA and sPFOA weaker effect of gas formation was observed. In [37] higher WCA for 240 min deposition than 20 min was obtained. However, the long deposition on steel caused very rough surface with macroscopic cracks tending to delaminate. Increasing the macroscopic roughness caused decrease of CAs and structural uniformity.
246
B. Pijáková et al. / Materials Letters 184 (2016) 243–247
The surface micrographs of sMA, sSA and sPFOA (see, Fig. 1) represent the layer morphology. Cluster-like formations of sMA, with possibility of trapping the air inside the structure, contributed to the superhydrophobic behavior. In case of sSA, cauliflower-like formations with fine structuring in nanometer scale (inset on Fig. 1) were observed. For both, sMA and sSA, presence of cracks in the layer referred to internal stress. Morphology of sPFOA was composed of plate-shaped formations creating the porous structure similar to zinc products in [38] enhancing the wettability based on Cassie-Baxter model. Existing formations were visibly smaller in case of sPFOA specimen. In magnification of 50 kx, round shape of plates is visible. Layer sPFOA approved to have no visible cracks, providing enhanced adhesion observed during the placement in low pressure chamber, whereas sMA and sSA resulted to delaminate from substrate. 3.4. Tribological tests The indentation resistance of studied films was low mainly because of the film porosity, the hardness was in the range from 1 to 3 MPa and the elastic modulus ranged from 0.3 to 1.0 GPa. Scratch tests of sMA and sSA samples showed plastic deformation of the film up to penetration depths reaching approximately half of the film thickness, when the substrate plastic deformation started to be dominating. The films were gradually worn out by the indenter up to complete uncovering of the substrate, what approved oneself with abrupt increase in friction coefficient. The friction coefficient of the studied films was relatively low, in the range from 0.1 to 0.25. Adhesive failures were observed neither for sMA nor for sSA samples. sPFOA samples showed cracking and chipping at the edges of the crack tracks when the penetration depths exceeded the film thickness due to dominative substrate plastic deformation. Inside the crack track the film behavior was similar to samples sMA and sSA.
PFOA spectrum were present in sPFOA at 2925 and 2854 cm 1. The change in bonding was observed, indicating the coordinated (– COO ) at 1681 and 1448 cm 1, referring to the production of carboxylate. The bands at 1201 and 1143 cm 1 allocated to (–CF2) groups confirmed the successful retention of fluorine bonded to hydrocarbon chain [38,43].
4. Conclusions In this contribution, superhydrophobic and superoleophobic layer on stainless steel was prepared by one-step time-saving electrodeposition. Introducing the aqueous solution provides the preference to deposition from PFOA aqueous solution. The twenty min electrodeposition applying 5 V resulted in layer with WCA 159°, OCA 153° and surface energy of 0.6 mJ/m2. Achieved characteristics were caused by plate-like porous microstructure and preservation of fluorine confirmed by SEM, EDX and IR spectroscopy. On the contrary, products of MA and SA were completely wetted by olive oil with WCA 156° and 151° and surface energy 16.10 and 11.4 mJ/m2. Thus, presented methodology is very promising for intensifying the wider use of PFOA.
Acknowledgment This work was supported by Masaryk University, project number GA 13-20031S funded by Czech Science Foundation, project number TACR TE02000011 funded by Technology Agency of Czech Republic, project number CZ.1.05/2.1.00/03.0086 funded by European Regional Development Fund and project LO1411(NPU I) funded by Ministry of Education Youth and Sports of Czech Republic. Authors would like to thank Mgr. David Pavliňák, Ph.D. for SEM, Ing. Pavel Franta for ATR-FTIR measurements and our external partner Synpo, a.s. for corrosion testing.
3.5. Chemical composition Measured values of carbon, oxygen, fluorine and lanthanum stated in wt% by EDX in Table S2 (Supplementary material) provided elemental ratio of lanthanum myristate and lanthanum stearate. The ratio for sMA, C:La:O ¼5.4:1.17:1, corresponded to lanthanum myristate, similarly as in [34,37,39,40] while ratio of sSA, C:La:O ¼6.5:1.27:1, was in good agreement with lanthanum stearate [31,32,41]. Obvious difference between the sMA/sSA and sPFOA was the presence of fluorine in a sPFOA. In addition to obtained surface structure, fluorine content enhanced hydrophobicity and induced the oil-repellency [10]. For this reason, sPFOA is more suitable as liquid-repellent surface for low surface tension liquids. Resembling the shortened IR spectra of precursors and samples in Fig. 2 provided evidences of chemical reactions proceeding during deposition (for more information, see Supplementary material). MA spectrum contained the characteristic vibrations at 2954, 2918, 2848 cm 1 attributed to the hydrocarbon groups (–CH3), (–CH2) and (–CH2) respectively. The band at 1703 cm 1 demonstrated the presence of free (–COO), indicating unmodified MA. Spectrum of sMA contained the bands for the same hydrocarbon groups at 2956, 2916 and 2850 cm 1, however the presence of coordinated (–COO ) moieties at 1531 and 1448 cm 1 signalized the modified MA and confirmed the production of lanthanum myristate [33]. SA (sSA) spectrum was analogue to MA (sMA) because of similar bonding. Bands of (– COO ) at 1533 and 1446 cm 1 classify the salt of SA in sSA. In correlation to EDX analysis, superhydrophobic lanthanum stearate was created similarly to [31,42]. Unreacted PFOA was characterized by bands at 1758 cm 1 ascribed to (–COO) and (–CF2) indicated by 1203 and 1147 cm 1. Absenting bands of (–CH2) in
Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2016.08.078.
References [1] K. Liu, Y. Tian, L. Jiang, Bio-inspired superoleophobic and smart materials: design, fabrication, and application, Prog. Mater. Sci. 58 (2012) 503–564, http: //dx.doi.org/10.1016/j.pmatsci.2012.11.001. [2] Z. Chu, S. Seeger, Superamphiphobic surfaces, Chem. Soc. Rev. 43 (2014) 2784–2798, http://dx.doi.org/10.1039/c3cs60415b. [3] H.J. Butt, I.V. Roisman, M. Brinkmann, P. Papadopoulos, D. Vollmer, C. Semprebon, Characterization of super liquid-repellent surfaces, Curr. Opin. Colloid Interface Sci. 19 (2014) 343–354, http://dx.doi.org/10.1016/j. cocis.2014.04.009. [4] D. Gennes, Wetting, Statics and Dynamics, 57, 1985. [5] R.N. Wenzel, Resistance of solid surfaces to wetting by water, J. Ind. Eng. Chem. 28 (1936) 988–994, http://dx.doi.org/10.1021/ie50320a024. [6] A.B.D. Cassie, Of Porous Surfaces, 1944 546–551. 〈http://pubs.rsc.org/en/con tent/articlepdf/1944/tf/tf9444000546〉. [7] Z. Xue, M. Liu, L. Jiang, Recent developments in polymeric superoleophobic surfaces, J. Polym. Sci. Part B: Polym. Phys. 50 (2012) 1209–1224, http://dx.doi. org/10.1002/polb.23115. [8] S. Yang, X. Jin, K. Liu, L. Jiang, Nanoparticles assembly-induced special wettability for bio-inspired materials, Particuology 11 (2013) 361–370, http://dx. doi.org/10.1016/j.partic.2013.02.001. [9] N. Valipour M., F.C. Birjandi, J. Sargolzaei, Super-non-wettable surfaces: a review, Colloids Surf. A: Physicochem. Eng. Asp. 448 (2014) 93–106, http://dx. doi.org/10.1016/j.colsurfa.2014.02.016. [10] T. Jiang, Z. Guo, W. Liu, Biomimetic superoleophobic surfaces: focusing on their fabrication and applications, J. Mater. Chem. A 3 (2015) 1811–1827, http://dx. doi.org/10.1039/C4TA05582A. [11] K. Liu, X. Yao, L. Jiang, Recent developments in bio-inspired special wettability,
B. Pijáková et al. / Materials Letters 184 (2016) 243–247
Chem. Soc. Rev. 39 (2010) 3240, http://dx.doi.org/10.1039/b917112f. [12] C. Pereira, C. Alves, A. Monteiro, C. Magén, A.M. Pereira, A. Ibarra, et al., Designing novel hybrid materials by one-pot co-condensation: from hydrophobic mesoporous silica nanoparticles to superamphiphobic cotton textiles, ACS Appl. Mater. Interfaces (2011), http://dx.doi.org/10.1021/am200220x. [13] C. Jin, J. Li, S. Han, J. Wang, Q. Sun, A durable, superhydrophobic, superoleophobic and corrosion-resistant coating with rose-like ZnO nanoflowers on a bamboo surface, Appl. Surf. Sci. 320 (2014) 322–327, http://dx.doi.org/ 10.1016/j.apsusc.2014.09.065. [14] K. Ellinas, S.P. Pujari, D.A. Dragatogiannis, C.A. Charitidis, A. Tserepi, H. Zuilhof, et al., Plasma micro-nanotextured, scratch, water and hexadecane Resistant, Superhydrophobic, and Superamphiphobic polymeric Surfaces with perfluorinated Monolayers, ACS Appl. Mater. Interfaces 6 (2014) 6510–6524, http: //dx.doi.org/10.1021/am5000432. [15] N. Wang, Z. Zhu, J. Sheng, S.S. Al-Deyab, J. Yu, B. Ding, Superamphiphobic nanofibrous membranes for effective filtration of fine particles, J. Colloid Interface Sci. 428 (2014) 41–48, http://dx.doi.org/10.1016/j.jcis.2014.04.026. [16] D. Ge, L. Yang, C. Wang, E. Lee, Y. Zhang, S. Yang, A multi-functional oil–water separator from a selectively pre-wetted superamphiphobic paper, Chem. Commun. 51 (2015) 6149–6152, http://dx.doi.org/10.1039/C4CC09813G. [17] J. Li, L. Yan, Q. Ouyang, F. Zha, Z. Jing, X. Li, et al., Facile fabrication of translucent superamphiphobic coating on paper to prevent liquid pollution, Chem. Eng. J. 246 (2014) 238–243, http://dx.doi.org/10.1016/j.cej.2014.02.062. [18] V.A. Ganesh, S.S. Dinachali, H.K. Raut, T.M. Walsh, a S. Nair, S. Ramakrishna, Electrospun SiO2 nanofibers as a template to fabricate a robust and transparent superamphiphobic coating, RSC Adv. 3 (2013) 3819, http://dx.doi.org/ 10.1039/c3ra22968h. [19] X. Zhu, Z. Zhang, G. Ren, X. Men, B. Ge, X. Zhou, Designing transparent superamphiphobic coatings directed by carbon nanotubes, J. Colloid Interface Sci. 421 (2014) 141–145, http://dx.doi.org/10.1016/j.jcis.2014.01.026. [20] N. Wang, D. Xiong, Y. Deng, Y. Shi, K. Wang, Mechanically robust superhydrophobic steel surface with anti-icing, UV-durability, and corrosion resistance properties, ACS Appl. Mater. Interfaces (2015), http://dx.doi.org/ 10.1021/acsami.5b00558. [21] N. Valipour Motlagh, F.C. Birjandi, J. Sargolzaei, N. Shahtahmassebi, Durable, superhydrophobic, superoleophobic and corrosion resistant coating on the stainless steel surface using a scalable method, Appl. Surf. Sci. 283 (2013) 636–647, http://dx.doi.org/10.1016/j.apsusc.2013.06.160. [22] N. Valipour Motlagh, J. Sargolzaei, N. Shahtahmassebi, Super-liquid-repellent coating on the carbon steel surface, Surf. Coat. Technol. 235 (2013) 241–249, http://dx.doi.org/10.1016/j.surfcoat.2013.07.039. [23] L. Feng, Y. Che, Y. Liu, X. Qiang, Y. Wang, Fabrication of superhydrophobic aluminium alloy surface with excellent corrosion resistance by a facile and environment-friendly method, Appl. Surf. Sci. 283 (2013) 367–374, http://dx. doi.org/10.1016/j.apsusc.2013.06.117. [24] L. Liu, J. Zhao, Y. Zhang, F. Zhao, Y. Zhang, Fabrication of superhydrophobic surface by hierarchical growth of lotus-leaf-like boehmite on aluminum foil, J. Colloid Interface Sci. 358 (2011) 277–283, http://dx.doi.org/10.1016/j. jcis.2011.02.036. [25] X. Zhu, Z. Zhang, X. Men, J. Yang, X. Xu, Rapid formation of superhydrophobic surfaces with fast response wettability transition, ACS Appl. Mater. Interfaces (2010), http://dx.doi.org/10.1021/am100808v. [26] L. Liu, F. Xu, L. Ma, Facile fabrication of a superhydrophobic Cu surface via a selective etching of high-energy facets, J. Phys. Chem. C. 116 (2012) 18722–18727, http://dx.doi.org/10.1021/jp302794p. [27] K. Li, X. Zeng, H. Li, X. Lai, A study on the fabrication of superhydrophobic iron surfaces by chemical etching and galvanic replacement methods and their anti-icing properties, Appl. Surf. Sci. 346 (2015) 458–463, http://dx.doi.org/ 10.1016/j.apsusc.2015.03.130.
247
[28] W. Liang, L. Zhu, W. Li, H. Liu, Facile fabrication of a flower-like CuO/Cu(OH)2 nanorod film with tunable wetting transition and excellent stability, RSC Adv. 5 (2015) 38100–38110, http://dx.doi.org/10.1039/C5RA04359J. [29] M. Alonso Frank, A.R. Boccaccini, S. Virtanen, A facile and scalable method to produce superhydrophic stainless steel surface, Appl. Surf. Sci. 311 (2014) 753–757, http://dx.doi.org/10.1016/j.apsusc.2014.05.152. [30] L. Hao, Y. Sirong, H. Xiangxiang, L. Enyang, Z. Yan, Colloids and surfaces A: physicochemical and engineering aspects fabrication of superhydrophobic and oleophobic surface on zinc substrate by a simple method, Colloids Surf. A: Physicochem. Eng. Asp. 469 (2015) 271–278, http://dx.doi.org/10.1016/j. colsurfa.2015.01.037. [31] Y. Huang, D.K. Sarkar, X.G. Chen, A one-step process to engineer superhydrophobic copper surfaces, Mater. Lett. 64 (2010) 2722–2724, http://dx.doi. org/10.1016/j.matlet.2010.09.010. [32] Y. Huang, D.K. Sarkar, D. Gallant, X.G. Chen, Corrosion resistance properties of superhydrophobic copper surfaces fabricated by one-step electrochemical modification process, Appl. Surf. Sci. 282 (2013) 689–694, http://dx.doi.org/ 10.1016/j.apsusc.2013.06.034. [33] Q. Liu, Z. Kang, One-step electrodeposition process to fabricate superhydrophobic surface with improved anticorrosion property on magnesium alloy, Mater. Lett. 137 (2014) 210–213, http://dx.doi.org/10.1016/j. matlet.2014.09.010. [34] Z. Chen, L. Hao, A. Chen, Q. Song, C. Chen, A rapid one-step process for fabrication of superhydrophobic surface by electrodeposition method, Electrochim. Acta 59 (2012) 168–171, http://dx.doi.org/10.1016/j. electacta.2011.10.045. [35] J. Niu, H. Lin, C. Gong, X. Sun, Theoretical and experimental insights into the electrochemical mineralization mechanism of perfluorooctanoic acid, Environ. Sci. Technol. 47 (2013) 14341–14349, http://dx.doi.org/10.1021/es402987t. [36] H. Lin, J. Niu, S. Ding, L. Zhang, Electrochemical degradation of perfluorooctanoic acid (PFOA) by Ti/SnO2–Sb, Ti/SnO2–Sb/PbO2 and Ti/SnO2–Sb/ MnO2 anodes, Water Res. 46 (2012) 2281–2289, http://dx.doi.org/10.1016/j. watres.2012.01.053. [37] Z. Chen, L. Hao, C. Chen, A fast electrodeposition method for fabrication of lanthanum superhydrophobic surface with hierarchical micro-nanostructures, Colloids Surf. A: Physicochem. Eng. Asp. 401 (2012) 1–7, http://dx.doi.org/ 10.1016/j.colsurfa.2012.02.020. [38] H. Meng, S. Wang, J. Xi, Z. Tang, L. Jiang, Facile means of preparing superamphiphobic surfaces on common engineering metals, J. Phys. Chem. C. 112 (2008) 11454–11458, http://dx.doi.org/10.1021/jp803027w. [39] Q. Liu, D. Chen, Z. Kang, One-step electrodeposition process to fabricate corrosion-resistant superhydrophobic surface on magnesium alloy, ACS Appl. Mater. Interfaces 7 (2015) 1859–1867, http://dx.doi.org/10.1021/am507586u. [40] C. Zhilei, S. Maobing, W. Lida, Cathodic etching for fabrication of super-hydrophobic aluminum coating with micro/nano-hierarchical structure, J. Solid State Electrochem. 17 (2013) 2661–2669, http://dx.doi.org/10.1007/ s10008-013-2141-0. [41] Y. Huang, D.K. Sarkar, X.G. Chen, Fabrication of superhydrophobic surfaces on aluminum alloy via electrodeposition of copper followed by electrochemical modification, Nano-Micro Lett. 3 (2011) 160–165, http://dx.doi.org/10.3786/ nml.v3i3.p160-165. [42] J. Li, X. Liu, Y. Ye, H. Zhou, J. Chen, A simple solution-immersion process for the fabrication of superhydrophobic cupric stearate surface with easy repairable property, Appl. Surf. Sci. 258 (2011) 1772–1775, http://dx.doi.org/10.1016/j. apsusc.2011.10.042. [43] X. Xu, Z. Zhang, W. Liu, Fabrication of superhydrophobic surfaces with perfluorooctanoic acid modified TiO2/polystyrene nanocomposites coating, Colloids Surf. A: Physicochem. Eng. Asp. 341 (2009) 21–26, http://dx.doi.org/ 10.1016/j.colsurfa.2009.03.028.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Facile electrodeposition of superhydrophobic and oil-repellent thick layers on steel substrate Barbora Pijáková n, Miloš Klíma, Milan Alberti, Vilma Buršíková Department of Physical Electronics, Masaryk University, 267/2 Kotlářská, Brno CZ-61137, Czech Republic
art ic l e i nf o
a b s t r a c t
Article history: Received 25 January 2016 Received in revised form 20 June 2016 Accepted 13 August 2016 Available online 15 August 2016
The aim of this work is to produce liquid-repellent surface on stainless steel via simple electrodeposition. For this purpose, myristic acid, stearic acid ethanol solution and perfluorooctanoic acid aqueous solution were used. Resulting contact angles and surface energy values were studied. Superhydrophobic and superoleophobic behavior of samples prepared using perfluorooctanoic acid electrolyte were performed by contact angle 159° for deionized water, 153° for olive oil and low surface energy 0.60 mJ/m2. Relation between the non-wettable behavior of samples, surface structure, chemical composition and mechanical properties were observed by SEM with EDX analysis, FTIR spectroscopy and tribological measurement, giving the preference to fluorinated precursor and low voltage electrodeposition. & 2016 Elsevier B.V. All rights reserved.
Keywords: Electrodeposition Superhydrophobicity Superoleophobicity Functional surface Perfluorooctanoic acid
1. Introduction A repellency of the surfaces for various liquids is the point of the interest for many research teams [1,2]. Characterization of non-wettable behavior is realized by measuring the contact angle (CA) values of liquids on the surface [3]. As the result of the theoretical aspects introducing the Young's equation, Wenzel and Cassie-Baxter wetting models [4–6], the roles of surface energy, surface morphology and surface tension are crucial. For perspective application, there are two necessary steps to reach the repellency, namely creation of an appropriate morphology and the modification of surface energy by suitable chemical composition [7,8]. The bioinspiration lead to mimicking of natural morphology and production of artificial surfaces in laboratory conditions [9– 11]. An application of liquid-repellent products introduces the large quantity of possible substrates for modification such as textiles [12], wood [13], plastics [14,15], paper [16,17] or glass [18,19]. Important substrates for industry are metals. The hybrid surface modification consists of enhancing the surface roughness with inorganic nanoparticles or chemical etching and additive modification of nanoparticles by organic precursors such as fluorinated organic compounds [20–22]. Many research teams present the preparation of superhydrophobic surface on metals such as aluminum [1,23,24], copper [25,26] or iron [27] by long-time n
Corresponding author. E-mail address: [email protected] (B. Pijáková).
http://dx.doi.org/10.1016/j.matlet.2016.08.078 0167-577X/& 2016 Elsevier B.V. All rights reserved.
immersions of substrate with modified structure in stearic acid (SA), myristic acid (MA) [28,29] with analogue results given by replacing the precursors with perfluorooctanoic acid (PFOA) [30], providing water and oil repellency. Two-step methods consisting of the microstructure formation and hydrophobization were replaced by controlled electrolysis with ethanol solution of SA or MA as electrolytes [31,32–34]. This method is time-saving, simple and effective for metal substrate modification. However, the products exhibit no repellency for low surface tension liquids. Herein, we report simple time-saving deposition method of liquid-repellent layers on the stainless steel. Furthermore, by introducing of PFOA in electrolyte, water and oil repellent coatings are formed, prioritizing PFOA before non-fluorinated organic acids requiring addition of inorganic salt. Substitution of ethanol with water in electrolyte containing PFOA could help to solve the problem of acid persistence in water [35,36] by recycling the contaminated fraction of water. Deposited layers can be applied to enhance the corrosion resistance or to introduce functional properties such anti-icing and self-cleaning.
2. Experimental 2.1. Materials and methods 2.1.1. Materials PFOA (Alfa Aesar, 95%), MA (Alfa Aesar, 98%), lanthanum(III) chloride heptahydrate (LaCl3 7H2O, Alfa Aesar, 99%), SA (Lachema,
244
B. Pijáková et al. / Materials Letters 184 (2016) 243–247
Table 1 CA values for testing liquids and calculated surface free energy. Liquid CA [deg] Sample
Distilled water
Glycerol
Ethylene glycol
Diiodomethane
Formamide
1-bromonaphthalene
Surface free energy [mJ/m2]
sMA sSA sPFOA
1567 2 151 73 1597 2
149 7 5 148 7 8 1547 3
148 74 1397 8 1527 2
106 7 11 122 77 1417 3
1507 3 1427 12 1417 4
637 28 64 7 19 1447 5
16.10 11.40 0.60
Fig. 1. SEM micrographs of surface structure (magnification 10 kx), inset of image detail (magnification 50 kx) and water droplet with stated WCA for sMA, sSA and sPFOA samples.
95%), potassium bromide (KBr, Sigma Aldrich, Z99%), ethanol (Sigma-Aldrich, 95%), glycerol (Sigma-Aldrich, Z99%), 1-bromonaphthalene, ethyleneglycol (Sigma-Aldrich, Z99.5%), diiodomethane (Sigma-Aldrich, 99%), formamide (Sigma-Aldrich, Z99.5%) and deionized water (conductivity 18.18 mS/cm at 13 °C; prepared at Masaryk university using RO 1-1CC unit by MEMSEP Ltd.) were used for experiments. 2.1.2. Surface characterization CA and surface energy values, averaged from ten measurements, were obtained by Surface Energy Evaluation (see) System device with eponymous software (AdveX Instruments) for 2.5 μl droplets. The surface energy was determined using the six-liquid Owens-Wendt regression model. Norm-referenced neutral salt spray (NSS) corrosion tests were realized for 1000 h according to CSN EN ISO 9227 NSS to observe possible corrosion product formation. Macroscopic topography and surface roughness was characterized by confocal microscope Olympus LEXT OLS4000 operating with LEXT software. For microstructure observation, SEM Tescan MIRA3 using secondary electron (SE) detector was employed. Each sample was coated by 19 nm of gold in order to prevent surface charging. The film thickness was measured using DektakXT (Bruker) mechanical profilometer. The mechanical properties of the films were studied using TI950 (Hysitron) and Fischerscope H100 nanoindenters. The scratch resistance and film adhesion were studied by means of Revetest Xpress plus scratch tester (Anton Paar) equipped with a Rockwell type diamond indenter with a radius of 200 mm. The load was increased at a constant rate 16 N/min, while the scratch length was 16 mm. Occurrence of chemical elements from precursors was stated in wt% by SEM-EDX mapping of the 25 mm2 area. FTIR spectrometer Bruker VERTEX 80v equipped with attenuated total reflectance (ATR) plate measured reflectance spectra of samples on steel substrate and transmittance spectra of KBr pellets containing pure precursors (concentration up to 1%). 2.2. Electrodeposition Stainless steel plates 20 70 1.5 mm in size were cleaned in
ethanol, ethanol/deionized water, deionized water ultrasonic bath, each for 15 min and dried with the airflow. Electrolytes with concentration of 0.1 M MA and 0.038 M of LaCl3 7H2O in ethanol, 0.05 M SA with 0.038 M LaCl3 7H2O in ethanol and 0.045 M PFOA in deionized water were prepared two hours prior the deposition. The distance between the electrodes was two centimeters. Using DC power supply DF3010 (Wentronic GmbH), working conditions were set to 30 V for 10 min for MA electrolyte according to [37], 15 V for 10 min for SA and 5 V for 20 min for PFOA solution. Optimal working conditions for SA and PFOA electrolytes were optimized in dependence on water CA (WCA) (see Table S1 Supplementary material). After the deposition termination, samples were retained in a fume hood until dried.
3. Results and discussion 3.1. Contact angle and surface energy measurement WCA values were stated 156 72°, 1517 3° and 159 72° for prepared samples sMA, sSA and sPFOA respectively, exhibiting superhydrophobic behavior. However, the CA for olive oil (OCA) with surface tension of E32 mN/m was impossible to state for sMA and sSA due to their oleophilicity. OCA for sPFOA was stated in a range of 15373° exhibiting superoleophobic behavior. The high liquid CAs ensure the perspective usage of PFOA products. The Table 1 contains the CA values for liquids and surface energies, that were stated 16.10 mJ/m2, 11.40 mJ/m2 and 0.60 mJ/m2 for sMA, sSA and sPFOA, respectively. Low deviations for sPFOA CA values predict eligible material uniformity. The Meng et al. [38] referred that surface energy exceeding the one-quarter of the liquid surface tension result in wettable behavior (CA o90°). This fact fitted to surface energies of sMA, sSA and sPFOA in relation to OCA. The significant change of sPFOA surface energy corresponded to the presence of fluorine. Reproducibility of layers was considerable, providing low deviations for numerous WCAs measurement (see, Table S2).
B. Pijáková et al. / Materials Letters 184 (2016) 243–247
245
Fig. 2. IR spectra of deposited samples sMA, sSA, sPFOA and unmodified precursors MA, SA, PFOA with marked bands of characteristic groups vibrations.
3.2. Corrosion testing After 1000 h in NSS chamber, no evidence of corrosion product formation was observed for sMA, sSA an sPFOA. Thus, the deposition and produced layers do not support or initiate corrosion processes. 3.3. Structure observation Surface thickness was 2376 mm, 137 4 mm, 12 72 mm, whereas roughness was 26 mm, 10 mm and 8 mm for sMA, sSA and
sPFOA, respectively (see Fig. S1 in Supplementary material). The roughness was related to applied voltage, in terms of enhancing surface formation growth and gas bubbles production with increasing voltage. For sMA, visible raising bubbles paths were created. In comparison to sSA and sPFOA weaker effect of gas formation was observed. In [37] higher WCA for 240 min deposition than 20 min was obtained. However, the long deposition on steel caused very rough surface with macroscopic cracks tending to delaminate. Increasing the macroscopic roughness caused decrease of CAs and structural uniformity.
246
B. Pijáková et al. / Materials Letters 184 (2016) 243–247
The surface micrographs of sMA, sSA and sPFOA (see, Fig. 1) represent the layer morphology. Cluster-like formations of sMA, with possibility of trapping the air inside the structure, contributed to the superhydrophobic behavior. In case of sSA, cauliflower-like formations with fine structuring in nanometer scale (inset on Fig. 1) were observed. For both, sMA and sSA, presence of cracks in the layer referred to internal stress. Morphology of sPFOA was composed of plate-shaped formations creating the porous structure similar to zinc products in [38] enhancing the wettability based on Cassie-Baxter model. Existing formations were visibly smaller in case of sPFOA specimen. In magnification of 50 kx, round shape of plates is visible. Layer sPFOA approved to have no visible cracks, providing enhanced adhesion observed during the placement in low pressure chamber, whereas sMA and sSA resulted to delaminate from substrate. 3.4. Tribological tests The indentation resistance of studied films was low mainly because of the film porosity, the hardness was in the range from 1 to 3 MPa and the elastic modulus ranged from 0.3 to 1.0 GPa. Scratch tests of sMA and sSA samples showed plastic deformation of the film up to penetration depths reaching approximately half of the film thickness, when the substrate plastic deformation started to be dominating. The films were gradually worn out by the indenter up to complete uncovering of the substrate, what approved oneself with abrupt increase in friction coefficient. The friction coefficient of the studied films was relatively low, in the range from 0.1 to 0.25. Adhesive failures were observed neither for sMA nor for sSA samples. sPFOA samples showed cracking and chipping at the edges of the crack tracks when the penetration depths exceeded the film thickness due to dominative substrate plastic deformation. Inside the crack track the film behavior was similar to samples sMA and sSA.
PFOA spectrum were present in sPFOA at 2925 and 2854 cm 1. The change in bonding was observed, indicating the coordinated (– COO ) at 1681 and 1448 cm 1, referring to the production of carboxylate. The bands at 1201 and 1143 cm 1 allocated to (–CF2) groups confirmed the successful retention of fluorine bonded to hydrocarbon chain [38,43].
4. Conclusions In this contribution, superhydrophobic and superoleophobic layer on stainless steel was prepared by one-step time-saving electrodeposition. Introducing the aqueous solution provides the preference to deposition from PFOA aqueous solution. The twenty min electrodeposition applying 5 V resulted in layer with WCA 159°, OCA 153° and surface energy of 0.6 mJ/m2. Achieved characteristics were caused by plate-like porous microstructure and preservation of fluorine confirmed by SEM, EDX and IR spectroscopy. On the contrary, products of MA and SA were completely wetted by olive oil with WCA 156° and 151° and surface energy 16.10 and 11.4 mJ/m2. Thus, presented methodology is very promising for intensifying the wider use of PFOA.
Acknowledgment This work was supported by Masaryk University, project number GA 13-20031S funded by Czech Science Foundation, project number TACR TE02000011 funded by Technology Agency of Czech Republic, project number CZ.1.05/2.1.00/03.0086 funded by European Regional Development Fund and project LO1411(NPU I) funded by Ministry of Education Youth and Sports of Czech Republic. Authors would like to thank Mgr. David Pavliňák, Ph.D. for SEM, Ing. Pavel Franta for ATR-FTIR measurements and our external partner Synpo, a.s. for corrosion testing.
3.5. Chemical composition Measured values of carbon, oxygen, fluorine and lanthanum stated in wt% by EDX in Table S2 (Supplementary material) provided elemental ratio of lanthanum myristate and lanthanum stearate. The ratio for sMA, C:La:O ¼5.4:1.17:1, corresponded to lanthanum myristate, similarly as in [34,37,39,40] while ratio of sSA, C:La:O ¼6.5:1.27:1, was in good agreement with lanthanum stearate [31,32,41]. Obvious difference between the sMA/sSA and sPFOA was the presence of fluorine in a sPFOA. In addition to obtained surface structure, fluorine content enhanced hydrophobicity and induced the oil-repellency [10]. For this reason, sPFOA is more suitable as liquid-repellent surface for low surface tension liquids. Resembling the shortened IR spectra of precursors and samples in Fig. 2 provided evidences of chemical reactions proceeding during deposition (for more information, see Supplementary material). MA spectrum contained the characteristic vibrations at 2954, 2918, 2848 cm 1 attributed to the hydrocarbon groups (–CH3), (–CH2) and (–CH2) respectively. The band at 1703 cm 1 demonstrated the presence of free (–COO), indicating unmodified MA. Spectrum of sMA contained the bands for the same hydrocarbon groups at 2956, 2916 and 2850 cm 1, however the presence of coordinated (–COO ) moieties at 1531 and 1448 cm 1 signalized the modified MA and confirmed the production of lanthanum myristate [33]. SA (sSA) spectrum was analogue to MA (sMA) because of similar bonding. Bands of (– COO ) at 1533 and 1446 cm 1 classify the salt of SA in sSA. In correlation to EDX analysis, superhydrophobic lanthanum stearate was created similarly to [31,42]. Unreacted PFOA was characterized by bands at 1758 cm 1 ascribed to (–COO) and (–CF2) indicated by 1203 and 1147 cm 1. Absenting bands of (–CH2) in
Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2016.08.078.
References [1] K. Liu, Y. Tian, L. Jiang, Bio-inspired superoleophobic and smart materials: design, fabrication, and application, Prog. Mater. Sci. 58 (2012) 503–564, http: //dx.doi.org/10.1016/j.pmatsci.2012.11.001. [2] Z. Chu, S. Seeger, Superamphiphobic surfaces, Chem. Soc. Rev. 43 (2014) 2784–2798, http://dx.doi.org/10.1039/c3cs60415b. [3] H.J. Butt, I.V. Roisman, M. Brinkmann, P. Papadopoulos, D. Vollmer, C. Semprebon, Characterization of super liquid-repellent surfaces, Curr. Opin. Colloid Interface Sci. 19 (2014) 343–354, http://dx.doi.org/10.1016/j. cocis.2014.04.009. [4] D. Gennes, Wetting, Statics and Dynamics, 57, 1985. [5] R.N. Wenzel, Resistance of solid surfaces to wetting by water, J. Ind. Eng. Chem. 28 (1936) 988–994, http://dx.doi.org/10.1021/ie50320a024. [6] A.B.D. Cassie, Of Porous Surfaces, 1944 546–551. 〈http://pubs.rsc.org/en/con tent/articlepdf/1944/tf/tf9444000546〉. [7] Z. Xue, M. Liu, L. Jiang, Recent developments in polymeric superoleophobic surfaces, J. Polym. Sci. Part B: Polym. Phys. 50 (2012) 1209–1224, http://dx.doi. org/10.1002/polb.23115. [8] S. Yang, X. Jin, K. Liu, L. Jiang, Nanoparticles assembly-induced special wettability for bio-inspired materials, Particuology 11 (2013) 361–370, http://dx. doi.org/10.1016/j.partic.2013.02.001. [9] N. Valipour M., F.C. Birjandi, J. Sargolzaei, Super-non-wettable surfaces: a review, Colloids Surf. A: Physicochem. Eng. Asp. 448 (2014) 93–106, http://dx. doi.org/10.1016/j.colsurfa.2014.02.016. [10] T. Jiang, Z. Guo, W. Liu, Biomimetic superoleophobic surfaces: focusing on their fabrication and applications, J. Mater. Chem. A 3 (2015) 1811–1827, http://dx. doi.org/10.1039/C4TA05582A. [11] K. Liu, X. Yao, L. Jiang, Recent developments in bio-inspired special wettability,
B. Pijáková et al. / Materials Letters 184 (2016) 243–247
Chem. Soc. Rev. 39 (2010) 3240, http://dx.doi.org/10.1039/b917112f. [12] C. Pereira, C. Alves, A. Monteiro, C. Magén, A.M. Pereira, A. Ibarra, et al., Designing novel hybrid materials by one-pot co-condensation: from hydrophobic mesoporous silica nanoparticles to superamphiphobic cotton textiles, ACS Appl. Mater. Interfaces (2011), http://dx.doi.org/10.1021/am200220x. [13] C. Jin, J. Li, S. Han, J. Wang, Q. Sun, A durable, superhydrophobic, superoleophobic and corrosion-resistant coating with rose-like ZnO nanoflowers on a bamboo surface, Appl. Surf. Sci. 320 (2014) 322–327, http://dx.doi.org/ 10.1016/j.apsusc.2014.09.065. [14] K. Ellinas, S.P. Pujari, D.A. Dragatogiannis, C.A. Charitidis, A. Tserepi, H. Zuilhof, et al., Plasma micro-nanotextured, scratch, water and hexadecane Resistant, Superhydrophobic, and Superamphiphobic polymeric Surfaces with perfluorinated Monolayers, ACS Appl. Mater. Interfaces 6 (2014) 6510–6524, http: //dx.doi.org/10.1021/am5000432. [15] N. Wang, Z. Zhu, J. Sheng, S.S. Al-Deyab, J. Yu, B. Ding, Superamphiphobic nanofibrous membranes for effective filtration of fine particles, J. Colloid Interface Sci. 428 (2014) 41–48, http://dx.doi.org/10.1016/j.jcis.2014.04.026. [16] D. Ge, L. Yang, C. Wang, E. Lee, Y. Zhang, S. Yang, A multi-functional oil–water separator from a selectively pre-wetted superamphiphobic paper, Chem. Commun. 51 (2015) 6149–6152, http://dx.doi.org/10.1039/C4CC09813G. [17] J. Li, L. Yan, Q. Ouyang, F. Zha, Z. Jing, X. Li, et al., Facile fabrication of translucent superamphiphobic coating on paper to prevent liquid pollution, Chem. Eng. J. 246 (2014) 238–243, http://dx.doi.org/10.1016/j.cej.2014.02.062. [18] V.A. Ganesh, S.S. Dinachali, H.K. Raut, T.M. Walsh, a S. Nair, S. Ramakrishna, Electrospun SiO2 nanofibers as a template to fabricate a robust and transparent superamphiphobic coating, RSC Adv. 3 (2013) 3819, http://dx.doi.org/ 10.1039/c3ra22968h. [19] X. Zhu, Z. Zhang, G. Ren, X. Men, B. Ge, X. Zhou, Designing transparent superamphiphobic coatings directed by carbon nanotubes, J. Colloid Interface Sci. 421 (2014) 141–145, http://dx.doi.org/10.1016/j.jcis.2014.01.026. [20] N. Wang, D. Xiong, Y. Deng, Y. Shi, K. Wang, Mechanically robust superhydrophobic steel surface with anti-icing, UV-durability, and corrosion resistance properties, ACS Appl. Mater. Interfaces (2015), http://dx.doi.org/ 10.1021/acsami.5b00558. [21] N. Valipour Motlagh, F.C. Birjandi, J. Sargolzaei, N. Shahtahmassebi, Durable, superhydrophobic, superoleophobic and corrosion resistant coating on the stainless steel surface using a scalable method, Appl. Surf. Sci. 283 (2013) 636–647, http://dx.doi.org/10.1016/j.apsusc.2013.06.160. [22] N. Valipour Motlagh, J. Sargolzaei, N. Shahtahmassebi, Super-liquid-repellent coating on the carbon steel surface, Surf. Coat. Technol. 235 (2013) 241–249, http://dx.doi.org/10.1016/j.surfcoat.2013.07.039. [23] L. Feng, Y. Che, Y. Liu, X. Qiang, Y. Wang, Fabrication of superhydrophobic aluminium alloy surface with excellent corrosion resistance by a facile and environment-friendly method, Appl. Surf. Sci. 283 (2013) 367–374, http://dx. doi.org/10.1016/j.apsusc.2013.06.117. [24] L. Liu, J. Zhao, Y. Zhang, F. Zhao, Y. Zhang, Fabrication of superhydrophobic surface by hierarchical growth of lotus-leaf-like boehmite on aluminum foil, J. Colloid Interface Sci. 358 (2011) 277–283, http://dx.doi.org/10.1016/j. jcis.2011.02.036. [25] X. Zhu, Z. Zhang, X. Men, J. Yang, X. Xu, Rapid formation of superhydrophobic surfaces with fast response wettability transition, ACS Appl. Mater. Interfaces (2010), http://dx.doi.org/10.1021/am100808v. [26] L. Liu, F. Xu, L. Ma, Facile fabrication of a superhydrophobic Cu surface via a selective etching of high-energy facets, J. Phys. Chem. C. 116 (2012) 18722–18727, http://dx.doi.org/10.1021/jp302794p. [27] K. Li, X. Zeng, H. Li, X. Lai, A study on the fabrication of superhydrophobic iron surfaces by chemical etching and galvanic replacement methods and their anti-icing properties, Appl. Surf. Sci. 346 (2015) 458–463, http://dx.doi.org/ 10.1016/j.apsusc.2015.03.130.
247
[28] W. Liang, L. Zhu, W. Li, H. Liu, Facile fabrication of a flower-like CuO/Cu(OH)2 nanorod film with tunable wetting transition and excellent stability, RSC Adv. 5 (2015) 38100–38110, http://dx.doi.org/10.1039/C5RA04359J. [29] M. Alonso Frank, A.R. Boccaccini, S. Virtanen, A facile and scalable method to produce superhydrophic stainless steel surface, Appl. Surf. Sci. 311 (2014) 753–757, http://dx.doi.org/10.1016/j.apsusc.2014.05.152. [30] L. Hao, Y. Sirong, H. Xiangxiang, L. Enyang, Z. Yan, Colloids and surfaces A: physicochemical and engineering aspects fabrication of superhydrophobic and oleophobic surface on zinc substrate by a simple method, Colloids Surf. A: Physicochem. Eng. Asp. 469 (2015) 271–278, http://dx.doi.org/10.1016/j. colsurfa.2015.01.037. [31] Y. Huang, D.K. Sarkar, X.G. Chen, A one-step process to engineer superhydrophobic copper surfaces, Mater. Lett. 64 (2010) 2722–2724, http://dx.doi. org/10.1016/j.matlet.2010.09.010. [32] Y. Huang, D.K. Sarkar, D. Gallant, X.G. Chen, Corrosion resistance properties of superhydrophobic copper surfaces fabricated by one-step electrochemical modification process, Appl. Surf. Sci. 282 (2013) 689–694, http://dx.doi.org/ 10.1016/j.apsusc.2013.06.034. [33] Q. Liu, Z. Kang, One-step electrodeposition process to fabricate superhydrophobic surface with improved anticorrosion property on magnesium alloy, Mater. Lett. 137 (2014) 210–213, http://dx.doi.org/10.1016/j. matlet.2014.09.010. [34] Z. Chen, L. Hao, A. Chen, Q. Song, C. Chen, A rapid one-step process for fabrication of superhydrophobic surface by electrodeposition method, Electrochim. Acta 59 (2012) 168–171, http://dx.doi.org/10.1016/j. electacta.2011.10.045. [35] J. Niu, H. Lin, C. Gong, X. Sun, Theoretical and experimental insights into the electrochemical mineralization mechanism of perfluorooctanoic acid, Environ. Sci. Technol. 47 (2013) 14341–14349, http://dx.doi.org/10.1021/es402987t. [36] H. Lin, J. Niu, S. Ding, L. Zhang, Electrochemical degradation of perfluorooctanoic acid (PFOA) by Ti/SnO2–Sb, Ti/SnO2–Sb/PbO2 and Ti/SnO2–Sb/ MnO2 anodes, Water Res. 46 (2012) 2281–2289, http://dx.doi.org/10.1016/j. watres.2012.01.053. [37] Z. Chen, L. Hao, C. Chen, A fast electrodeposition method for fabrication of lanthanum superhydrophobic surface with hierarchical micro-nanostructures, Colloids Surf. A: Physicochem. Eng. Asp. 401 (2012) 1–7, http://dx.doi.org/ 10.1016/j.colsurfa.2012.02.020. [38] H. Meng, S. Wang, J. Xi, Z. Tang, L. Jiang, Facile means of preparing superamphiphobic surfaces on common engineering metals, J. Phys. Chem. C. 112 (2008) 11454–11458, http://dx.doi.org/10.1021/jp803027w. [39] Q. Liu, D. Chen, Z. Kang, One-step electrodeposition process to fabricate corrosion-resistant superhydrophobic surface on magnesium alloy, ACS Appl. Mater. Interfaces 7 (2015) 1859–1867, http://dx.doi.org/10.1021/am507586u. [40] C. Zhilei, S. Maobing, W. Lida, Cathodic etching for fabrication of super-hydrophobic aluminum coating with micro/nano-hierarchical structure, J. Solid State Electrochem. 17 (2013) 2661–2669, http://dx.doi.org/10.1007/ s10008-013-2141-0. [41] Y. Huang, D.K. Sarkar, X.G. Chen, Fabrication of superhydrophobic surfaces on aluminum alloy via electrodeposition of copper followed by electrochemical modification, Nano-Micro Lett. 3 (2011) 160–165, http://dx.doi.org/10.3786/ nml.v3i3.p160-165. [42] J. Li, X. Liu, Y. Ye, H. Zhou, J. Chen, A simple solution-immersion process for the fabrication of superhydrophobic cupric stearate surface with easy repairable property, Appl. Surf. Sci. 258 (2011) 1772–1775, http://dx.doi.org/10.1016/j. apsusc.2011.10.042. [43] X. Xu, Z. Zhang, W. Liu, Fabrication of superhydrophobic surfaces with perfluorooctanoic acid modified TiO2/polystyrene nanocomposites coating, Colloids Surf. A: Physicochem. Eng. Asp. 341 (2009) 21–26, http://dx.doi.org/ 10.1016/j.colsurfa.2009.03.028.