Surface Preparation: Some Techniques

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Non-wetting surfaces are surfaces that promote dropwise condensation. However, most raw surfaces have high free surface energy and exhibit high-wetting behavior. Accordingly, in most practical applications, lowering the surface energy becomes a prerequisite to achieving the dropwise mode of condensation. Five surface engineering techniques, namely silanization of glass, chemical texturing of copper, anodization of aluminum, laser micro-machining of the copper surface, and ion implantation, are discussed. Although each technique is distinct in nature, all of them work on modifying the surface texture and/or chemical properties to develop non-wettable surfaces. Chemical texturing of glass is performed by silanation using octyl-decyl-tri-chloro-silane (C18H37C13Si) in a chemical vapor deposition process. Copper surface is coated with a low surface energy material 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 9, 9, 10, 10, 10-heptadecafluoro-1-decanethiol (CF3(CF2)7CH2CH2SH) to promote dropwise condensation. Physical texturing of aluminum is achieved by anodic oxidation of the material to generate the structured nanopores on the surface to lower the free surface energy. In the case of laser machining, material evaporation using laser ablation process is adopted to develop the desired physical structures on the surface, typically on the microscale length. Irradiation via Argon ion beams of 0.5 keV is executed on copper, aluminum, and gold surfaces to lower the surface energy by implanting the foreign molecules of very low dispersive energy inside the surface. It is demonstrated that different techniques can be adopted to fabricate the non-wetting surfaces, the surfaces which aid in dropwise condensation. Therefore, depending on the material of the surface in actual applications, one can choose a technique to envisage the dropwise condensation.