Preparation Of Nano Alumina For Superhydrophobic Surfaces

Recently, inspired by the "lotus effect", superhydrophobic surfaces with a water contact angle(CA) higher than 150° and a tilting angle(TA) less than 5°, have attracted much interest due to the potential in both fundamental research and practical applications including anti-icing coatings, selfcleaning, oil–water separation, corrosion resistance, antibacterial coatings and so on. It is wellknown that the the "lotus effect" is attributed to its unique low surface energy epicuticular wax and its micro/nano scale hierarchical structures. Varied components have been used to fabricate superhydrophobic surfaces on different substrates. Nano alumina materials have been chosen by many reserachers for their low cost, low toxicity and controllable structure or size, which were used to prepare superhydrophobic surface on varied substrates. The main points of this dissertation are summarized as follows:1. Polyvinylpyrrolidone(PVP) boehmite hybrid thin film was deposited onto glass by sol–gel dip-coating method. The Fabry-Pérot fringe in visible spectra was applied to monitor the multilayer film thickness growth. Field-emission scanning electron microscope and Atomic force microscope were used to characterize the film’s microstructure. The film was composed of uniform boehmite nanoparticles about 20 nm. Addition of PVP in the boehmite sol was effective in increasing the critical thickness of the films. When the as-deposited films were sintered at 500 °C, the boehmite was transformed to γ-Al2O3 with the decreased film thickness.2. A new approach for the fabrication of γ-Al OOH nanoflake films has been developed. The nanoflakes were successfully formed on a glass substrate via a simple, low temperature, and seed-assisted hydrothermal technique. A large amount of γ-Al OOH nanoflakes with various thicknesses interlaced together, resulting in a nest-like layer of film with their sharp edges nearly vertical to glass substrates. The effects of hydrothermal temperature, time and concentration on the morphology and phase of the γ-Al OOH nanoflake films are investigated. X-ray powder diffraction, field emission scanning electron microscopy and Raman microscopy were used to characterize the structures and morphologies of the films. The growth mechanism of the γ-Al OOH nanoflake films was also discussed. Moreover, the nanostructural films of γ-Al OOH showed a transition from hydrophilic to super-hydrophobic with the chemical vapor deposition of trichloro(1H,1H,2H,2H-perfluorooctyl) silane(PFOS).3. An interesting morphological evolution from single nanosheet to nanosheet assemblies and flower-like nanostructures boehmite(γ-Al OOH) on quartz surface was discovered via a facile hydrothermal synthetic method. The effects of hydrothermal temperature and time on the morphology and phase of the flower-like boehmite films were studied systematically. The formation mechanism of the flower-like boehmite had also been investigated. The flower-like γ-Al2O3 was prepared by calcining the hierarchical boehmite at 500 °C for 2 h, preserving the same morphology during the thermal transformation process. Applying this method to modify alumina membrane, 3D flowerlike structure of γ-Al OOH nanoflakes were sucessfully grown on alumina membrane, and after modified by PFOS, the alumina membrane shows good superhydrophobic property.4. A super-hydrophobic aluminum alloy surface with multi-scale hierarchical flower-like boehmite(γ-Al OOH) structure has been fabricated via a facile hydrothermal approach. The different morphologies of the γ-Al OOH films were totally controlled by the preparation conditions for crystal growth, such as reaction solution and time. The morphology and structure of the films were characterized by using FTIR, XRD, FE-SEM and TEM. The superhydrophobicity can be attributed to both the rough multi-scale structural boehmite coating and surface enrichment of low surface energy with the chemical vapor deposition of 1H,1H,2H,2Hperfluorodecyltriethoxysilane(POTS). The resulting super-hydrophobic surface exhibits a water contact angle of 155° and a sliding angle of about 5°. The corrosion behavior was investigated with corrosion test in nitrate solution and it was found that the super-hydrophobic coating considerably improved the corrosion resistant performance of aluminum alloy.5. Nanosheet γ-Al OOH and silica spheres composite thin film was deposited onto glass by sol–gel dip-coating method through hydrolysis of boiling water immersion. The hierarchical structures silica films were obtained by sequentially dip-coating of two different sizes silica sol individually(80 and 400 nm). Then the silica films were dipped into the alumina sol for the formation of silica and alumina two composite films. Finally, the composite films were immersed in boiling water for 1 h, which induced the formation of γ-Al OOH nanosheets. The super-hydrophobicity with high adhesion forces can be attributed to both the rough multi-scale structural coating and surface enrichment of low surface energy with the chemical vapor deposition of POTS.