Fabrication and theoretical explanation of the superhydrophobic CuZn coating with dandelion-like CuO microstructure
Introduction
Pipeline steel is an important metal in the field of pipeline transportation. However, the adhesion of the aqueous mixture to the pipe wall has the negative influence on production and transportation, which results in much economic loss and waste of resources. Therefore, fabricating a superhydrophobic coating on pipeline steel surface to decline the adhesion of the aqueous mixture to the pipeline steel surface is necessary. Recently, superhydrophobic surface has become a major topic of research because of its various applications, such as self-cleaning property [1], corrosion resistance [2], anti-icing property [3], and anti-scaling potential [4], which are directly related to our daily life. Moreover, a number of creatures with excellent hydrophobic property in nature, including lotus leaves [5], peanut leaves [6], water striders [7], and nepenthes pitcher plants [8], have been observed that the combined effect of the hierarchical micro-nano structure and the low surface energy material achieves the superhydrophobicity. However, the contact angle of water droplet on the smooth solid surface with the lowest surface free energy (6.7 mJ/m2) was only 119° [9]. Consequently, the hierarchical micro-nano structure plays the key role in fabricating the superhydrophobic surface [10].
Up to now, many methods have been used to fabricate hierarchical micro-nano structures for obtaining the superhydrophobic surface [11], [12], [13], [14], [15], and a great many of different hierarchical structured superhydrophobic surfaces have been fabricated successfully, including mushroom-like structure [16], caterpillar-like structure [17], pinecone-like structure [18], rose-like structure [19], etc.
In recent years, researchers have used the simple chemical oxidation to fabricate all kinds of CuO structures for obtaining the hierarchical structures, and the prepared CuO films show excellent superhydrophobic property after being modified with fluoride [20]. Moreover, chemical oxidation method is low cost, time saving, and facile condition [21]. However, to the best of our knowledge, various superhydrophobic CuO microstructures were mainly fabricated on the copper substrate without the steel substrate [22], and it lacked the theoretical model for explaining the reason for superhydrophobic.
In this paper, a superhydrophobic CuZn coating with dandelion-like CuO film was obtained on X90 pipeline steel surface. Furthermore, for the purpose of theoretical analysis, the dandelion-like microstructure was seen as the dual-scale structure that was composed of spherical and pillared microstructures. Based on the Wenzel's and Cassie's formulas, we confirmed the wetting state between water droplet and the dandelion-like structured superhydrophobic coating surface was the stable Cassie-Cassie state.
Section snippets
Materials and reagents
X90 pipeline steel was obtained from TGRC of China and cut into the size of 20 × 50 × 3 mm. Brass (H62) was purchased from the common market and cut into the size of 20 × 50 × 5 mm. Absolute ethanol (AR), acetone (AR), sodium hydroxide (NaOH, AR), and sulfuric acid (H2SO4, 98%) were purchased from West Long Chemical Co., Ltd. Sodium carbonate anhydrous (Na2CO3), trisodium phosphate dodecahydrate (Na3PO4·12H2O), sodium metasilicate nonahydrate (Na2SiO3·9H2O), Copper(II) sulfate pentahydrate (CuSO
Fabrication and characterization of the superhydrophobic coating
In order to fabricate a superhydrophobic coating on steel surface, the polished steel was first electrodeposited CuZn coating, and then immersed in the mixed solution including KOH and (NH4)2S2O8 to form CuO dandelion-like microstructure. Finally, the steel surface with dandelion-like structured coating was modified with pentadecafluorooctanoic acid anhydrous ethanol.
Fig. 1 shows the surface morphology and chemical composition of the steel sample under different conditions. The surface
Conclusion
In conclusion, a superhydrophobic CuZn coating with dandelion-like CuO microstructure was successfully prepared on X90 pipeline steel surface via a simple method including electrodeposition, chemical oxidation and fluorination. The dandelion-like microstructure was seen as the dual-scale structure composed of spherical and pillared microstructures. According to the theoretical explanation, it was confirmed that the wetting state between water droplet and the superhydrophobic coating with
Acknowledgements
The authors acknowledge the financial support of the National Natural Science Foundation of China (No. 51075184), the Fundamental Research Funds for the Central Universities (No. 15CX06059A), the Postgraduate Innovation Project of China University of Petroleum (East China) (No. YCXJ2016036).
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