Preparation And Characterization Of Superhydrophobic Films On Steel

Wettability is a significant property of solid surface, which can be judged by contact angle of water. Recently, the superhydrophobic surfaces with the contact angle larger than 150°have aroused lots of interests for their applications in anticorrosion, self-cleaning and anti-oxidization. It has been found that the wettability of the materials is determined by the roughness and surface free energy. Generally, two ways were employed to prepare the superhydrophobic surfaces:firstly, modified the rough surfaces with low surface energy materials; secondly, built fine structures on the hydrophobic surfaces. In this paper, steel was chosen as the substrate, chemical etching and hydrothermal method were used to build the micro-nano hierarchical structure and fluorinated silane was used to lower the surface free energy. The surfaces showed excellent hydrophobility after being self-assembled by fluorinated silane. The main contents are as follows:1. The effective self-assembled conditions were achieved by comparing the effects of self-assembly of fluorinated silane under different conditions. Generally, the preferable result can be acquired in the concentration of 4%(FT-922:water:ethanol=4:6:90), at 30℃for 12h. The hydrophobility can be improved, when steel was self-assembled with siloxane coupling agent, followed by modified with fluorine-containing reagents.2. Chemical etching was used to build the fine structures on the surfaces of the steel. Fluorinated silane was then used to hydrophobize those rough surfaces. The morphology, wettability and corrosion resistance of the resultant surfaces were characterized by means of scanning electron microscopy (SEM), water contact angle measurement and electrochemical measurement. SEM showed that loose structures with many gaps appeared on the surfaces after chemical etching. It exhibited superhydrophobic properties after being fluorinated, with water contact angles of 157.11°, as well as roll-off angles of less than 10°for 5μl drops. Polarization curves showed that the superhydrophobic films hindered the corrosive media via physical separation.3. Hydrothermal method was used to fabricate the fine structures on the surfaces of the steel. Fluorinated silane was then used to reduce the surface free energy. The morphology, chemical composition, wettability and corrosion resistance of the resultant surfaces were characterized by means of scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XRD), water contact angle measurement and electrochemical measurement. SEM showed that octahedron-like, flower-like and cauliflower-like micro-structures appeared on the surfaces after the hydrothermal process. XRD showed that the composition of the oxidation layer was Fe3O4. It exhibited superhydrophobic properties after being fluorinated, with water contact angles of 165.31°, as well as roll-off angles of less than 5°for 5μl drops. Polarization curves showed that the superhydrophobic film hindered the corrosive media via physical separation.Steel is a widely used engineering material. Superhydrophobic surfaces have unique advantages in self-cleaning and anti-corrosion. These two methods which we used to fabricate superhydrophobic surfaces were facile to operate and easy to control. The superhydrophobic steel surfaces have good stability and potential applications.