Study On Preparation And Characterization Of Superhydrophobic And Nano SiO₂ Composite Coating

Wettability is an important property governed by both the chemical composition and the microstructure of solid surfaces. Recently, inspired by the lotus effect superhydrophobic surfaces with water contact angle higher than 150° and rolling angle less than 10° have attracted much attention. In this dissertation, we reviewed the recent research on superhydrophobic surfaces and brought forward the investigation idea according to the previous literature data. We prepared the sol of SiO2 by using TEOS and Substituted hydrophilic of sol with hydrophobic group directly. This method possess many merits such as it can avoid using the expensive but have low surface energy of surface modifier-fluorine compounds, the experimental equipment and the process of the experiment is simple and controllable. The main work and innovation are listed as following:(1) First of all, we prepared the sol of SiO2 by hydrolysising TEOS, then using the PMMA substitute the hydrophilic-OH group and introduce the hydrophobic-CH3 group into the acidic silica sol. In order to prevent the film cracking, we added an amount of silicone resins. Finally, we obtained the hydrophobic films with the static contact angle greater than 90° by dip-coating method. Compared with the surface about monodisperse SiO2 coating, not only can we control the cracking of film, but also large number of nanoparticles cross-linked together to form micro-nano roughness structure, thus this film have good hydrophobicity. However, this film also have large rolling angle due to the high surface energy. So the water droplet can not free roll on the surface.(2) Secondly, we researched the difference of morphology, particle size of SiO2 film which prepared by hydrolysising TEOS with hydrochloric acid and ammonia as catalyst respectively, then we introduced the TMCS to replace the hydrophilic-OH group respectively with two kinds of catalysts. The experiment results showed that the particle size of SiO2 which used hydrochloric acid as catalyst is so small that the SiO2 particle easily cross-linked together and exhibited smooth surface when we use TMCS as hydrophobical modifier. Although certain number of low energy substance covered with the surface, the smooth surface leaded to the smaller roughness, then the static contact angle is small. So the performance of hydrophobic is poor with HC1 as catalyst. Furthermore, the particles of SiO2 would be linked together to form the cross-linked network structure with ammonia as catalyst. The film can form micro-nano roughness structure by the surface modification with TMCS. We could get the superhydrophobic coating. Anyway, the heat treatment process on both of film that discussed above should not exceed 250℃, otherwise the hydrophobic-CH3 group easily decomposed into the hydrophilic -OH group if around water vapor environment. The performance of superhydrophobic will decline.