Study On The Preparation And Properties Of Porous Silica Film

Surfaces with special wettability have been widely used in architecture, waterproof and bioengineering etc. In recent years, the preparation of surfaces with special wettability has attracted much attention, which is important to both fundamental research and practical applications. Herein, we reported an approach to create surfaces with special wettability from silica sol and studied the processes of preparing silica sol and super-hydrophilic and super-hydrophobic films, the primary results are as follows:Firstly, we prepared silica sol from waterglass by ion exchange method. The effects of silicon source concentration on pH, concentration of impurity elements, size and morphology of silica particles have been investigated and the regeneration processes of ion exchange resin have been researched. After exploring the processes for preparing silica sol, we determined the optimium parameters for preparing silica sol applied to different situations. When silica sol is used for preparing super-hydrophilic film, it is suitable to adjust the pH of silica sol to8.5-10. In this value, the films had good hydrophilicity and the silica sol were relatively stable, which can simplify the preparation process. Owing to the low concentration of silica sol required in this experiment, the disadvantage of energy consumption in enrichment process has been overcome. In addition, silica sol can also be used for preparing aerogel at ambient temperature and pressure after hydrophobic modification. In this case, it’s best to adjust the pH of silica sol to5to form gel. Therefore, the silica sol which is used for preparing super-hydrophobic SiO2aerogel film should be prepared at the right time, and can’t be stored for a long time.Secondly, we obtained silica sol with pH of0.9-3.0by ion exchange method and then adjusted it to alkaline. The pastes were prepared by mixing the additives and the silica sol. Then the hydrophilicity films were formed by coated it on the glasses. The optimized processes and paremeters were as follows:alkaline silica sol with ethanol, PEG, F127and terpineol were mixed in a volume ratio of30:60:5:5:1, the clean glass slides were immersed in the pastes for10s, pulled at the rate of2.2cm/s, and finally calcined at350℃for2h. The films hardness of5H, thickness of40nm and the initial CA of0°were obtained. The CA became7.2°after half a month, which was closed to the super-hydrophilic state. As a simple, efficient and low cost way to obtain super-hydrophilic film, it hold great prospect for practical application.Finally, we presented a process for preparing super-hydrophobic SiO2aerogel films. The optimum conditions were as follows. The concentration of waterglass was15%. The pH of silica sol was adjusted to5. The clean glass slides were immersed in the silica sol for10s, pulled at the rate of3cm/s, and dipped5times on same conditions. The coated glasses were immersed in deionized water for aging24h at60℃, modified in the mixture of HMDSO and HC1for12h at60℃, finally dried at ambient temperature and pressure. The CA of the films were153°, the highest transmittance was92.4%, the thickness was less than100nm, the porosity was70%, the refractive index was1.14and the density was0.7g/cm3. In our work, the deioned water was used for aging, which avoided the solvent exchange step, simplified the process and reduced the cost greatly. Further more, this method is environmentally friendly and has an attractive prospect.