Studies On Fabrication Of Superhydrophobic Surfaces On Alloy Substrates And The Wettability Of The Surfaces

Simple chemical etching and two-step chemical etching techniques are developed for fabricating superhydrophobic surfaces. Using these techniques, superhydrophobic surfaces have been prepared on alloyed brass, aluminum alloy, and stainless steel substrates.A hierarchical structure with micro- and nanostructures is fabricated on brass by Chemical etching in FeCl₃-HCl-H₂O solution. The structure consists of irregular pieces and fine papilla. After fluorination treating, the brass surface exhibits superhydrophobic properties, with a water contact angle of about 157°and contact angle hysteresis of about 5°. The effect of etching time on the hydrophobicity of the surfaces is investigated. The results indicate that the etching time plays an important role on the formation of hierarchical roughness. With XRD test, it was found that copper appeared on the surface of brass. The formation of micro-and nanostructures can be interpreted by dezincification mechanism, which includes preferential solution of zinc and resolution-redeposition theory. Also, the wettability of brass surface was discussed on the basis of Cassie theory.Two-step chemical etching with HF and HCl are used to produce rough surface on aluminum alloy substrate, and fluoroalkylsiane is then used to hydrophobize that rough surface. The resultant surface is examined by means of scanning electron microscopy (SEM), and water contact angle measurement. The results show that the surface is configured in a labyrinthic structure with cuboid plateaus and caves of micro-and nanostructure. This etched surface, when hydrophobized, exhibits superhydrophobic properties with water contact angle of about 156°, as well as contact angle hysteresis of about 5°. The orthogonal design was taken for the optimization. The content of etching time and etching concentration are measured for fixing on the optimum conditions. Also, the etched surface which without fluorination treating, exhibits superhydrophilic preoperties, and with a water contact angle of about 0°.Chemical etching is performed on stainless steel substrates, using FeCl₃-HCl-H₃PO₄- H₂O₂-H₂O solution. The hierarchical alveolate structures are fabricated on it, which consists of anomalistic caves and protuberances. Many fine papillae are filled in these protuberances. After fluorination treating, the stainless steel surface exhibits super-hydrophobic properties, with a water contact angle of about 160°and contact angle hysteresis of about 3°. Droplet which is suspended on a microsyringe is investigated to explain the effect of nanostructures combined with anisotropic micropatterns on the surface hydrophobicity, and this structure with low water adhesion and extremely low drag resistance. Superhydrophobic stainless steel surfaces have great importance in fundamental research and potential for industrial applications due to stainless steel is used in many field and superhydrophobic surfaces endowed with unique properties, such as resistance to corrosion and self-cleaning and reducing flow resistance.