A comparative study of the morphology and wetting characteristics of micro/nanostructured Cu surfaces for phase change heat transfer applications

A comparative study of oxidation methods to create Cu surfaces with controlled wettability is reported. Micro/nanostructures of Cu oxides are formed on Cu substrates using different chemical and thermal oxidation methods. The morphology and wetting characteristics of the resulting surfaces are characterized using atomic force microscopy, scanning electron microscopy, X-ray diffraction, and contact angle measurements. Chemical oxidation in alkali solutions can form uniform copper oxide layers with high roughness factors without causing thermal stress problems that often hamper thermal oxidation. By combining chemical oxidation with a hydrophobic coating, a wide range of wettability control is demonstrated from superhydrophilic (<10 degrees) to superhydrophobic (>170 degrees). Superhydrophilic CuO layers uniformly formed on Cu powder and Cu micropost wick surfaces lead to significant improvement in the capillary and heat transfer performance compared with comparable unoxidized Cu wicks. The present work motivates further studies to exploit the benefits of nanostructured Cu surfaces in various phase change heat transfer applications.