| With the development of science and technology, the requirements for properties of materials become higher and higher. In recent years, more and more attentions were paid on the superhydrophobic surfaces because of their extensive and attracted potential applications. Although many different kinds of methods were used to prepare super-hydrophobic surfaces, unfortunately, they have not been used widely due to the limitation of complicated processes and equipments. So it is the key of investigation to search after a kind of simple and practical method for preparing super-hydrophobic surface on large area. In this paper, based on the principle of'Lotus effect'and design of particles, the composite particles with different shapes were prepared by combining technique of composite nano-particles, sol-gel method with that of inorganic-organic emulsion polymerization. On the basis of investigation of the effects of composite particles on film surface structure and hydrophobicity, the hydrophobic films were made with low surface energy endowed with self-stratification fluorinated acrylates and rough surface structure provided by composite particles with special shape.First of all, the latex with low sureface energy and self-stratified ability was prepared by core-shell emulsion polymerization. The effects of polymerization conditions and varieties of fluorinated and silane monomers on hydrophobicity of film surface were investigated. The results of analysis on components and gradual distribution of film surface by X-ray photoelectronic spectrum (XPS) showed that fluorine may oriente on the air surface of film and distribute gradually in the film surface while silicon distribute bidirectionally. A small quantity of siloxane (C-1757) and functional monomers may improve the oriented ability of fluorine and water contact angle on the film which was increased to106°.Second, the nano-silica/polyacrylates composite emulsion and nano-silica/poly (fluorinated and siloxane acrylates) hydrophobic composite emulsion were prepared using silica particles prepared by sol-gel method as seeds and compound of anionic reactive and nonionic emulsifiers. The stability of composite emulsion, morphologies of composite particles and mechanism of organic-inorganic composite emulsion were discussed. The results of TEM showed that the morphology of composite particles and effect of encapsulation were influenced strongly by dosage and size of silica particles, surfactants, fluorinated and siloxane monomers. The shape of composite particles was petal-like with silica particle surrounded by spherical organic polymers when 80nm raw silica particles were used as seeds. The shell of composite particles became regular and thin with increase of dosage of silica and the diameters of them became small and even. The morphologies of composite particles were shown as strawberry-like and doublehemisphere-like after the fluorinated monomers and siloxane were introduced. However, they looked like doublehemisphere-like and snownman-like when the silica was modified with silicane coupling agent. This was brought about by the different polymerization mechanism. For raw silica/polyacrylates composite emulsion, the mechanism of polymer aggradation played dominant role. But for the raw silica/fluoro-siloxane-acrylates composite emulsion, the mechanisms of polymer aggradation and grafting on silica surface took leading role, respectively, during the period before and after fluorinated monomer and siloxane being added to the system, because of modifying and bridgework effects of siloxane. When the surface of silica used was modified, the mechanism of polymer grafting on silica surface became reigning. The effect of silica aggregating on the morphology of film surface was observed by AFM and it was shown that the surface roughness of film changed with the changes of diameter and dosage of used silica. As a result of the condensation between the silanol functional groups on SiO2 surface and that from hydrolysis of C-1757, it facilitated the enrichment of SiO2 particles on the surface of film when silicon orientating on the surface. Results of XPS showed that the content of fluorine in the outmost surface is higher than the calculated value and the fluorinated side chains enrich and orient toward the surface when C-1757 coexisted with silica. It was not influenced by silica particles because they were encapsulated evenly by fluoropolymer. But when raw SiO2 particles were added solely, phase separation between organic and inorganic plays an important role because of failed encapsulation so that the orientation on the surface of fluorine was restrained.Different sizes of silica particles and fluorosiloxane were used for controlling surface morphology and chemistry, respectively. The surface morphologies, roughness and the wettability on the surface of films containing different structural silica particles were compared. It was found that morphologies of silica beads have a strong influence on the WCA. For the film surface of singular diameter particles, the apparent water contact angles calculated from the Wenzel's model have a little difference with the measured results indicating that the Wenzel's formulation provides a approciate description for the water dewetting behavior on such structured surfaces. The dual size composite particles were obtained by utilizing the graft of different modified silica particles with epoxy functional group and amine functional group and then modified with fluorosiloxane. This makes the surface of film form a composite interface to have irregular binary structure as the lotus leaf surface which plays an essential role in trapping air between the substrate surface and the liquid droplets to reach the Cassie model. The differences of shape and sizes of dual-size particles make little effect on hydrophobicity and the roughness factor was unable to reflect the changes of contact angle. It was concluded that the dual-size composite particles made it easy to realize superhydrophobicity.The irregularly composite particles with quincunx-shape were obtained by utilizing the encapsulation and graft of silica particles through multistep emulsion polymerization. This makes the water contact angle on film surface increased to about 154°from 106°. Combining sol-gel method with organic-inorganic hybrid emulsion polymerization, the composite particles covered by silica particles were prepared to form irregular binary structure like lotus surface with superhydrophobic and self-cleaning properties. The water contact angle on the hybrid film is about 158°and hysteresis is less than 5°. This is expected to be a simple and practical method for preparing superhydrophobic and self-cleaning surfaces on large area. The fractal theory was used to evaluate the fractal dimension of composite film surface and the results indicated that the surface of composite film with dual-size roughness structure showed fractal characterization and the wetting behavior on rough surface accorded with the equation of water contact angle based on fractal factors. For the surface with dual roughness structure, fractal dimension may explain more clearly the effect of morphology on water contact angle. |
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