Preparation And Application Of Superhydrophobic Materials

Recently, preparation and application of superhydrophobic materials have drawn more and more applications due to its special advantage in some application fields, such as reducing flow resistance in microfluidic channels, separation of oil and water and self-cleaning surface. Further study revealed that the wettability of a surface was governed mainly by its chemical composition and geometrical structure. Accordingly, superhydrophobic surfaces have been constructed usually based on two essential concerns: (i) micro- and nano-scale hierarchical structures to increase the roughness of surface; (ii) chemical modification to reduce the surface energy of a rough surface. Based on these two principles, various techniques have been established to engineer superhydrophobic surfaces, with notable examples including layer-by-layer technique, electrochemical deposition, chemical vapor deposition and solution-immersion method. Through these approaches, lots of superhydrophobic materials have been fabricated. In this issue, we use lift-up soft-lithography and solution-immersion method to prepare a series of superhydrophobic materials. And then, these materials have been applied in the fields of corrosion resistance and separation of oil and water.In chapter 2, we have successfully fabricated a flexible superhydrophobic surface with a micrometer-level and nanometer-level hierarchical structure on PDMS films. Lift-up soft-lithography and chemical reduction led to the presence of a raspberry-like structure on the PDMS films; the hierarchical structure originated from coating ordered silica spheres with Ag NPs. SEM images have been used to evaluate the roughness of the PDMS films patterned with silica spheres which were decorated with Ag NPs. After modification of hydrophobic agent, the film displayed superhydrophobicity, the contact angle was about 154°and the sliding angle was about 4°. The effects of the amount of Ag NPs and the size of silica spheres on the wettability of the PDMS films have been investigated: the former played a major role on the wettability. Our superhydrophobic films could be easily transferred to a number of smooth substrates with different curvature. During the transfer process, the superhydrophobicity kept intact. Thus, our flexible superhydrophobic films could be used many times to satisfy a wide range of applications.In chapter 3, we have fabricated the two kinds of metal mesh which could be used for separating diesel oil and water by a solution-immersion process (including electroless galvanic deposition and dilute nitric acid etching). The surface of commercial copper mesh formed hierarchical structures which increased the roughness.After being modified by low surface energy agent such as HDT, the surfaces displayed superhydrophobicity and superoleophilicity simultaneously. The effect of pore size and pH values on wettability was investigated: the as-prepared meshes kept stable superhydrophobic and superoleophilic properties in the wide pore size ranging from 44μm to 490μm and in all range of pH values including extreme condition of pH = 0 and 14 for mesh prepared by solution-immersion method; while the application pH scope for mesh prepared by electroless galvanic deposition was from 1 to 14. If the PDT instead of HDT was grafted on the surface of as-prepared mesh, the surface showed superhydrophobicity and oleophobicity, which led to failure of separation of oil and water. The method present here was high efficiency, inexpensive and time-saving; it had potential for large scale production.In chapter 4, we have successfully fabricated metallic superhydrophobic materials by primary cell, with concurrent electric power generation. The superhydrophobicity of the Cu and Zn plates was very well preserved up to a month under ambient conditions. The superhydrophobic Cu plate has showed corrosion resistance over a whole range of pH values from 0 to 14; while the Zn plate could bear pH values from 3 to 13. Under the salt spray condition, the superhydrophobicity of Cu plate was kept up to 15 h, while the fabricated Zn plate was not resistant to the salt spray condition. The possible mechanism of the corrosion resistance was proposed: both the surface structure and self-assembled monolayer played important roles. The method presented here features facile fabrication of corrosion resistant materials, and more importantly, the materials fabrication process involved power generation, which was of great significance in both fundamental research and industrial applications. The present approach had promising potential in the commercialization of the corrosion protection of metallic materials.