Fabrication And Properties Of Superhydrophobic Self-cleaning Coatings

In recent years,superhydrophobic surfaces have attracted significant attention of sciencitists due to its special wettability and its potential application.Through the microscopic analysis of superhydrophobic organisms in nature,it's found that the hierarchical structures providing high surface roughness and a surface with low surface energy are the two key factors for the biologicals to form their superhydrophobic interface.Based on the biomimetic point of view and the theoretical basis established by scientists such as Wenzel,Cassie and Baxter for the superhydrophobic state,researchers had fabricated various superhydrophobic materials and obtained good application results.At present,the fabrication of superhydrophobic surfaces mainly showed the disadvantages of complicated process,special equipment,unsuitable for large-area substrates,poor abrasion-resistance resulting in poor hydrophobicity maintenance,which had a negative impact on the promotion of the superhydrophobic materials'application.In this thesis,at first,the micro-nano composite structure built by the self-assembly of ordinary nano-particles was used to improve the roughness of the matrix,while the PS resin was used to reduce the surface energy of the matrix and improve the adhesion between inorganic components and the matrix.The superhydrophobic coatings with a static contact angle?Contact Angle?more than 150°and a slide angle less than 10°had been fabricated on various of substrates.Our research not only solved the defects of current superhydrophobic surface fabrication methods,but also explored its application in concrete surface protection for the first time.Secondly,in order to avoide the uncontrollability of nanoparticles,micro/nano composite structure was built by using the bismuth oxyhalide 3D microspheres with micro-nano composite structure.Besides,the hydrophobicity of coatings was further enhanced and the photocatalytic activity and the thermal insulating function were exploited.The main contents and results of this paper could be summarized as follows:?1?The influence of the types of hydrophobic modifiers on the hydrophobicity of powders and coatings,the effects of the usage of nano-silica on the surface roughness and hydrophobicity of coatings were studied.Compared with HMDS,OTCS and HTS,FAS-SiO2 hydrophobically modified by FAS was found to be most hydrophobic with a CA of 137.8°and the corresponding coating's CA was 159.5°.The hydrophobicity of the coatings increased with the powder usage.When the powder usage reached 4wt%,a superhydrophobic coating with CA of 158.2°and SA of 8.7°could be fabricated.?2?The effect of coating's hydrophobicity on the protective performance of concrete surface was studied.With the increase of coating's CA,its surface protective effect on concrete was also enhanced.Compared with the blank specimen,the CA of the specimen coated with10wt%FAS-SiO₂ coating increased from 28.8°to 155.6°,While the samples'96h water absorption decreased by 27.12%,6h electric flux decreased by 51.39%,and chloride ion concentration at 50mm depth decreased by 42.3%.?3?The effects of morphology and the usage of the bismuth oxyhalide 3D microspheres on coatings's roughness and hydrophobicity had been studied.The more nanosheets grow on the surface of the microspheres and the tighter the nanosheet clusters,the more hydrophobic the coating was.The results show that the coating prepared by BiOBr microspheres with loose nanosheet clusters and Bi OBr_0.125Cl0.₈₇₅ microspheres with nanosheet clusters are 160.2°and168.5°,respectively,with SA values of 4.9°and 3.2°,respectively.?4?The visible light photocatalytic self-cleaning and thermal insulation properties of bismuth oxyhalide coatings were studied.The fabricated coating was found to degrade about91%rhodamine B dye for 15 min.The near-infrared reflectivity of the bismuth oxyhalide 3D microspheres is 85.96-93.69%.Compared with the aluminum plate coated with PS resin alone,the temperature of the upper surface of the aluminum plate coated with the bismuth oxyhalide coating was decreased by 4.1-8.6°C,and the temperature inside the incubator was reduced by1.2-3.9°C,showing a better thermal insulation effect.