Fabrication Of Superhydrophobic Surfaces And Applications In Selective Separation Of Liquids Differing In Surface Tention

Wettability of a solid surface is an important property which has been applied in various fields such as lubricating and friction of machines, printing and dyeing textile, coatings and so on. Superhydrophobic surfaces typically have a water contact angle higher than 150°and a low sliding angle (<10°). Because of their special surface properties, superhydrophobic surfaces can be potentially applied in diverse areas such as self-cleaning coatings, mico-fluidic devices, and friction-reduction coatings. Therefore, both academic and practical research attention has been focused on superhydrophobic surfaces.Studies have revealed that the surface wettability depends on the chemical composition and the morphology of the surface. Accordingly, various artificial superhydrophobic surfaces have been fabricated by constructing special hierarchical roughness on hydrophobic materials or modifying rough surfaces using materials with low free energy. However, most of these approaches can only be used to prepare small surface in laboratory. Meanwhile, the process is very complicated and the cost is relatively high. Especially, because the mechanical properties of the obtained surfaces are very poor, it is very difficult to employ these surfaces for practical applications. Therefore, it is crucial to develop fabrication method of large-scale superhydrophobic surfaces. In addition, owing to their low surface tensions, organic solvents can easily wet many superhydrophobic surfaces, which makes it possible to separate liquids differing in surface tensions with superhydrophobic surfaces. A few literatures have reported attempts to separate oil-water mixtures using superhydrophobic and superoleophilic meshes. However, the separation of liquids differing in surface tension especially miscible solutions with superhydrophobic surfaces has not been reported so far and the separation efficiency of oil-water mixtures still requires systematic investigation. This dissertation concentrated on developing two fabricating methods of superhydrophobic coatings. The first one is to fabricate superhydrophobic coatings on tile with a simple spray-and-dry approach using commercial available polyphenylene sulfide (PPS) and hydrophobic silica (H-SiO2) powder; and the second one is to generate superhydrophobic and superoleophilic coatings on filter paper/mesh with a dip-coating approach. The relationship between surface wettabilities and processing conditions was systematically studied, and the surfaces were applied to separate liquids differing in surface tension.1. Commercially available polyphenylene sulfide (PPS) and hydrophobic silica (H-SiO2) powder were used to fabricate superhydrophobic composite coatings on tile with a simple spray-dry method. The influence of thermal treatment temperature and weight ratio of raw materials on the surface wettability was investigated. The surface coating obtained at 280℃with the weight ratio of H-SiO2 to PPS 1:1 showed a water contact angle higher than 150°and a sliding angle lower than 4°. The surface coatings exhibited superhydrophobic properties for all the aqueous solutions with pH ranging from 1 to 14. Moreover, the as-prepared surfaces were stable and showed self-cleaning properties, implying possible applications in anti-dirty coatings.2. A simple dip-coating approach was used to endow filter paper with both superhydrophobic and superoleophilic properties. The specific wettability was used to separate liquid with low surface tension, such as diesel oil, from water. The treated filter paper could remove not only diesel oil floating on a water surface, but also emulsified oil in aqueous suspensions. In particular, it exhibited reproducible selective adsorption of a collection of organic solvents such as hexane and dodecane that reached 2.0-3.4 times its original weight. Moreover, the superhydrophobic filter paper was effectively used to separate oil and water, leading to a decrease in water content in the oil. The filter paper was also able to partly extract ethanol and isopropanol from aqueous solutions. Its reproducible and stable properties mean that the superhydrophobic filter paper is an ideal candidate for applications in the cleanup of oil pollutants and the separation of oil and water.3. Superhydrophobic and superoleophilic stainless steel mesh was also prepared with the above mentioned dip-coating approach. The surface coating with the weight ratio of H-SiO2 to PS 1:1 and thermally treated at 60℃showed a water contact angle of 154°and a sliding angle of 5°, with diesel oil spreading quickly on the modified surface. The as-prepared filter mesh was successfully used in separatiing oil-water mixtures and the separation efficiency was higher than 94.6% when the volume ratio of diesel oil to water was greater than 1:15.