Superhydrophobic Properties Of Copper Film By Electrical Brush-plating

As the most widely used engineering materials in human industrial activities, metal material is very important and irreplaceable, but some features of the metal also restrict its application in some fields. Roughness and surface free energy of the solid surface are two factors in wettability. Higher surface free energy of the metal will show hydrophilic properties, and thus it can be easily wetted and the corrosion occur. So the metal material is greatly limited in moist conditions or water environments. The property of metal material surface cannot be changed very easily, but if the microstructure and chemical composition of its surface can be changed and then make its surface hydrophobic even superhydrophobic, it will widely broaden the application areas of the metal material, and it will subvert the traditions of the metal materials' hydrophilic property. With the development of separate discipline and interdisciplines, theoretical research of solid surface wetting properties and technologies of preparation of solid surfaces with special wetting properties have made a great progress. "Lotus effect" is the hot issue in this research field. The state of drops which fall on the lotus leaf surface is totally different with other surfaces, and it can freely roll down the surface of a lotus leaf. The researchers found that this phenomenon occurs because the lotus leaf surface has a special microstructure and hydrophobic waxy layer. According to the existing theory and technical technologies, a lot of materials with special wetting properties, especially the super-hydrophobic material, have been made. Restricted by the theory and technology, the preparation of hydrophobic material generally involves chemical modification of the surface. As to metal materials, metal surface with chemical modification cannot meet the requirements of production applications for its thermal stability and mechanical properties, and it can easily lead to the destruction of its superhydrophobic surface in special circumstances. Moreover, good thermal conductivity and other properties of metal materials will be affected because of the chemical modification layer. Another important challenge is to build a structure that similar to the surface of lotus leaf. Unfortunately, the existing technology is very difficult to meet this requirement. In short, it will be a profound impact in theoretical research and practical applications, if we can modify the metal surface without chemical modification to be superhydrophobic, and even anisotropic wetting properties.In this article, with controlling the parameters of the brush-plating, we manufactured a series of directivity and no directivity structure on the copper surface through one step brush-plating process and reasonable allocation of electroplating solution. Morphology, crystal structure and chemical composition of the samples' surface are tested by scanning electron microscopy(SEM), field emission scanning electron microscope(FESEM), X-ray diffraction(XRD) and X-ray photoelectron spectroscopy(XPS), respectively. We also explore the impact of structure of the copper films' surface about wetting properties and the anisotropic wetting properties influenced by directivity of a copper film, respectively. The main findings are shown as follows:1. Lotus-like three-level classification microstructure is manufactured on the pretreated copper foil though improved one-step brush plating technology. We control the parameters, especially brush voltage(2.0~4.0V), and the solution concentration to achieve our goals. The three-level classification microstructure is made up of nanoscale grain structure, submicron convex structure and micron structure. They are stacked in order of size. And voltage change only controls micron structure.2. Directional samples were manufactured on the pretreated copper foil through improved brush plating technology. Water droplets roll down the directional copper film will show anisotropic wetting property. And the films also have the three-dimensional hierarchical microstructure obviously.3. According to the theory of wetting, the theoretical calculations and the wetting mechanism, we found that a good superhydrophobicity which only depend on structuring surface' structure of the copper, contact angle can reach 151°.