Fabrication of Superhydrophobic Conical Structures of Polysiloxane on Mg Plates Using an Immersion Process

Abstract

Superhydrophobic surfaces have drawn the attention of the scientific and industrial communities alike owing to their immense potential to contribute to fundamental research and practical applications. Superhydrophobic surfaces can be used in self-cleaning, ice resistance, and applications in nano-/micro-fluidic devices. Many biological surfaces such as the lotus leaf, and the legs of a water spider are water repellent. Notably, the structure and chemical properties of a surface are the key factors that determine the superhydrophobicity of the surface of a material. For instance, the numerous papillae on the lotus leaf are coated with wax, which is a low surface energy material. The papillae on the lotus leaf and the conical structures on legs of the water spider are crucial in lending superhydrophobic properties to the surfaces. Nano-/micro-binary structures on surfaces trap air and dramatically reduce the contact area between the surface and the water droplet. Superhydrophobic surfaces have been conventionally fabricated by creating nano-scale hierarchical structures and by coating the surfaces with materials of low-surface-energies. Fluorinated alkyl silanes and long chain fatty acids are commonly used as lowsurface-energy materials. However, Cassie-Baxter's model demonstrated that rough surface structures are important to retain air, as they cushion water droplets. Provided that a large amount of air is retained on the surface, the surface can be expected to show superhydrophobic properties. Therefore, an appropriate conformation and morphology of the surface are crucial factors to realize superhydrophobic surface properties. Many techniques including etching, sol-gel methods, phase-separation methods, electro chemical deposition, electrospinning, and lithography have been used to create rough surfaces. Conical nano-/micro-binary structures on the surface have received considerable attention because of their geometry and physical properties. Conical surface structures have been fabricated using a variety of materials. For instance, conical nanocarbon structures have been fabricated on a transparent and flexible substrate using an ion irradiation technique at low temperatures. These structures were found to exhibit superior field emission properties as compared to carbon nanotubes. In another example, nickel surfaces containing nano-/micro conical arrays were produced by electrodeposition in the presence of ethylenediamine. The modified nickel surfaces exhibited superhydrophobicity without requiring modification with low surface energy materials. Further nanoconical arrays of glass have also been obtained using a chemical etching process. Even though nanoconical structures have gained considerable focus for various applications ranging from electronic devices to the fabrication of superhydrophobic surfaces, materials that can be used for assembling nanoconical structures are limited. In the present work, we report a simple method to fabricate superhydrophobic surfaces containing nanoconical structures on Mg plates using fluorinated alkyl triethoxysilane and 1,6-diphosphonohexane. This one-step process is simple and can be applied to large surfaces.