Fabrication And Properties Of Superhydrophobic Surface And Organic/Inorganic Hybrid Superhydrophobic Coating

Recently, the superhydrophobic materials with special wetting behavior have been drawn intense concerns. The superhydrophobic materials not only have good water repellency, but also show great potential applications in the areas of self-cleaning, anti-corrosive, anti- icing, water/oil separation and pipeline transportation. Most of the fabrication methods always suffer problems of complicated fabrication process and high price of materials, some methods are even only applicable to specific substrate s. In addition, the existing models can not well explain the contact model of water droplet on the surface. In this work, etching was simply used to construct superhydrophobic surface on iron plate, and the anti- icing properties of superhydrophobic iron were investigated. Then the polysiloxane was used as low surface energy material and the nano-Si O2 was adopted to construct roughness for fabricating organic/inorganic hybrid superhydrophobic coating, and the superhydrophobic coating was applied to the preparation of superhydrophobic/superoleophilic filtration fabric with water/oil separation property. Additionally, the fluorine-containing polyacrylate latex(PFA) was synthesized and then combined with nano-Si O2 to fabricate PFA/Si O2 hybrid superhydrophobic coating which possessed good stability and could be applied to various substrates. The superhydrophobic/superoleophilic sponge was fabricated after depositing with PFA/Si O2 and was applied to the area of oil removal. Finally, the wetting behavior of water droplet with different temperature on the hydrophobic surface was studied and a revised model of water droplet on rough hydrophobic surface was proposed. The research contents and results are listed as following:Firstly, the hierarchical structures on iron surface were constructed by chemical etch of hydrochloric acid(HC l) solution or galvanic replacement of silver nitrate(Ag NO3) solution, and the superhydrophobic surfaces were successfully prepared by the subsequent hydrophobic modification with stearic acid. Effects of reactive concentration and time on the microstructure and water contact angle were investigated. In addition, the anti- icing properties of the superhydrophobic iron were also studied. Fourier transform infrared spectroscopy(FTIR) results showed that the stearic acid was chemically bonded onto the metal ion on the surface. With the increase of HC l concentration, the iron surface became rougher and the WCA increased. However, the Ag NO3 concentration had little effects on the wetting behavio r but high Ag NO3 concentration would lead to the formation of Ag dendritic crystals. The superhydrophobic iron showed excellent anti- icing properties. When a water droplet was icing on the superhydrophobic surface, the air between the water droplet and solid surface benefited the decrease of the solid- liquid contact areas and heat transfer. Meanwhile, the superhydrophobic iron maintained superhydrophobicity after 10 times of icing and de-icing cycle.Secondly, the polysiloxane/Si O2 hybrid superhydrophobic coating was prepared by spraying method using polysiloxane, which obtained by the curing reaction between hydroxyl- terminated poly(dimethylsiloxanes)(H-PDMS) and tetraethoxysilane(TEOS), as low surface energy materia l and hydrophobic nano-Si O2 for constructing roughness. The curing condition of polysiloxane was optimized. The effects of Si O2 content on the surface morphology and water contact angle were investigated, and the acid and base resistance, weatherability and thermal stability of superhydrophobic coating were also studied. In addition, the component and structure of superhydrophobic coating after calcination were evaluated by FTIR, TG-FTIR, scanning electron microscopy(SEM) and energy dispersive X-ray spectroscopy(EDS). The results showed that with the increase of Si O2 content, the surface became rougher and the WCA increased. When the mass ratio of Si O2 to polysiloxane was 0.3, the morphology of the coating exhibited random micro/nanostructure and the WCA reached 153.4 o. The polysiloxane/Si O2 hybrid superhydrophobic coating showed good acid and base corrosion resistance, excellent weatherability and high thermal stability. With the increase of calcination temperature from 100 oC to 400 oC, the coating maintained superhydrophobic and became transparent with the visible light transmittance increasing from 40 % to 78 %. When the calcination temperature was over 500 oC, the wetting behavior of the coating changed from superhydrophobicity to superhydrophilicity. The superhydrophobic/superoleophylic filtration fabric was obtained after coating with polysiloxane/Si O2 hybrid coating. The coated filtration fabric showed good abrasion resistance and could effectively separate the mixture of water and oil with a high separation efficiency of about 90%.Thirdly, the fluorine-containing polyacrylate(PFA) latex with polyacrylate core and fluorine-containing polyacrylate shell was successfully synthesized by the two-stage semicontinuous emulsion polymerization using methyl methacrylate(MMA) as hard monomer, butylacrylate(BA) as soft monomer, acrylic acid(AA) as functional monomer and dodecafluoroheptyl methacrylate(DFMA) as fluorine-containing monomer. Effects of DFMA and AA content on the polymerization and store stability, monomer conversion, particle size, Zeta potential, crosslinking degree, carboxyl groups distributions and latex morphology, as well as the glass transition temperature(Tg), WCA, water absorption ratio and mechanical properties of latex film were studied. It showed that the obtained latex possessed good stability, and exhibited core-shell structure and uniform dispersion with a particle size of about 120 nm. The introduction of DFMA would result in the decrease of monomer conversion and polymerization stability. With the increase of DFMA content, the monomer conversion and the absolute value of Zeta potential decreased, and the particle size and coagulum ratio increased. The introduction of AA made contributions to the increase of monomer conversion, crosslinking degree and the absolute value of Zeta potential, and the decrease of water absorption ratio, while had little effects on the mechanical and thermal properties of latex film. With the increase of AA content, more coagulums were obtained and the possibility of nucleation in aqueous phase increased, making the latex morphology change from spherical to plum blossom- like. In addition, the latex film possessed excellent thermal stability and water resistance.Fourthly, the PFA/Si O2 hybrid superhydrophobic coating was successfully fabricated by spraying using PFA emulsion as low surface energy material, hydrophobic nano-Si O2 for constructing roughness and ethanol as cosolvent. The effects of Si O2 content on the surface morphology and hydrophobicity were investigated. The acid and base resistance, weatherability and thermal stability of the hybrid coating were also studied. Results showed that when the mass ratio of Si O2 to PFA emulsion was 0.2, the surface showed hierarchical micro/nano structure with the roughness(Rq) increased to 173.6 nm, and the surface became superhydrophobic with a WCA over 150 o. The PFA/Si O2 hybrid coating showed superhydrophobicity to water droplets with p H value of 1-14, and it could keep superhydrophobicity after being heated at 250 oC for 5 h or exposed to ambient atmosphere for more than 3 months. In addition, the hybrid coating could be applied to various substrates through spraying. The superhydrophobic/superoleophilic sponge was fabricated after coating with PFA/Si O2 hybrid coating. The prepared sponge showed excellent stability toward toluene soaking and abrasion testing, and could selectively and effectively absorb oil from water with absorption capacity over 25 times of its own weight. More importantly, the sponge could be reused for many cycles while still maintaining high absorption capacity and good hydrophobicity.Fifthly, the wetting behavior of water droplets with different temperature on the polysiloxane/Si O2 hybrid superhydrophobic coating and their corresponding models on the hydrophobic surface were systematically studied. Then theoretical model of water droplet on the hydrophobic rough surface was revised based on the experiment results. It showed that with the increase of temperature of water droplet, the WCA on the hydrophobic surface decreased. When the temperature of water droplet rose from 20 oC to 50 oC, the WCA on the superhydrophobic coating decreased from 154.4° to 130.4°, and the sliding angle increased from 5° to 180°. The water droplet with high temperature would not destroy the surface composition and hierarchical structure, the decrease of WC A of water droplet at high temperature was caused by the decrease of surface tension and the expelling of air between water and solid surface. The water droplet on the rough hydrophobic surface(not reached superhydrophobic state) preferred to the transition state between Cassie and Wenzel model. The increase of roughness could capture more air between the water droplet and solid surface, which was beneficial for the increase of WC A of water droplet at 20 oC, but had little effects on the WCA of water droplet at 60 oC because of the expelling of air at high temperature. Compared with microstructures and nanostructures, the construction of micro/nanostructures on the flat hydrophobic surface for achieving superhydrophobicity was more favorable.