Preparation Of Superhydrophobic And Superoleophobic Zn Surfaces Via Electrochemical Etching Method

Superhydrophobic surface is a kind of special wettability surface and has been a hot topic in the field of surface science for its properties like excellent hydrophobicity, self-cleaning, corrosion resistance, anti-icing, friction reduction, and so on. However, the liquid with lower surface energy than water can easily pollute the superhydrophobic surfaces. For this reason, fabricating a surface with superhydrophobicity and superoleophobicity can greatly broaden the application. Zinc has been widely applied in construction, light industry, agriculture, automotive, household electrical industry and other fields. Researches show that it is an effective method to protect zinc byfabricating superhydrophobic surface on Zinc substrate.In this paper, electrochemical etching technology was used to fabricate superhydrophobic and superoleophobic surfaces on zinc substrate. In the theoretical part, the classical surface wettability theories have been generalized, as well as the influence of micro-structure on surface wettability. These work made a theoretical basement of fabricating special micro-structure surface through electrochemical etching. Theoretical method to keep metestable composition contact form was attained by analyzing transform energy barrier between wenzel and cassie contact model. The analysis of contact angle hysteresis shows that micro-nano hierarchical surface is an ideal self-cleaning surface and the influence of micro structure on surface wettability shows that the overhang structure is the key to superoleophobicity.In this paper, electrochemical etching process and surfaces with different morphology can be attained by controlling process parameters. The surface with lotus-like structures on zinc substrate shows superhydrophobicity after fluoride-treatment. The surface with overhang andreentrant structures on zinc substrate shows superoleophobicity after perfluorooctanoic acid treatment. The chemical composition has been analyzed using XRD and the morphology has been analyzed using SEM. Contact measurement equipment was applied to measure contact angle and rolling angle of different droplets.According to the analysis of microstructure and surface chemical compostion on zinc substrate, the anodic dissolution mechanism of Zn in the neutral mixed electrolyte was sorted out. The analysis of the influence of microstructure on surface wettability comfirmed that the overhang structure is the key to superoleophobicity. Besides, the processing conditions such as time, current density were investigated to determine their effects on the surface micromorphology and wettability. Compared with other methods, electrochemical etching does not require exacting processing parameters with high efficiency and environmental-friendly, thus can be widely applied in industrial manufacture.