Fabrication And Charaterization Of Superhydrophobic SiO₂Composite Films By Hydrothermal Process

Inspired by the “lotus effect”,more and more people focus on the research ofsuperhudrophobic surface. Super hydrophobic surface has the capacity ofself-cleaning. When the water drops on the surface, It will take the dirt away from thesurface in the rolling process. So super hydrophobic films has very wide applicationprospect in antipollution, preservative, antioxidant and other aspect. Thoughtanalysising and summarizing the theory of superhydrophobic surfaces, differentpreparation methods and the existing defects from other article publicated recently, onthis basis putting forward the assumption on the preparation of superhydrophobicfilms, and then t verifying and improving the ideas hrough continuous experiment.Supposed that TEOS was incompletely hydrolysised and prepared silica solwithout modification we can achieve superhydrophobic films from this silica sol,analysising the hydrophobic property in different composition ratio and hydrothermaltemperature. By testing the change in viscosity of the silica sol in differenthydrothermal time, explaining TEOS hydrolysis condensation process inhydrothermal conditions. Adding glacial acetic acid to the silica sol, We have newconclusion that glacial acetic acid accelerated the hydrolysis and condensation andgelation process.Mixing silica sol and aluminium chloride solution at room temperature, weachieved silica/alumina composite film from the mixed solution under hydrothermalcondition. We changed the particles density on the surface by adjusting the volumeratio of the silica sol and aluminium chloride solution. From the optical microscopepicture we can see thar the particle size is in0.5μm～1.5μm. The surface of theparticle is composed of closely packed pillar which is0.2nm~4.5nm in diameter and100nm in height and the nanometer pillar and micrometer particle consists of micro-nano rough structure. The films changed from superhyrophobilic tosuperhydrophobic after modified by trimethylchlorosilane, the water contact angle(WCA) is up to152.88°. The transmissivity of the glass plated with thesuperhydrophobic film changed very small, so the silica/alumina composite filmscan be used as window glasses due to its self-cleaning capacity and hightransmissivity.Mixing silica sol and zinc chloride solution at room temperature, by changing theamount of TEOS, we can be successfully prepared various morphologies of films from the mixed solution under hydrothermal condition. When the volume of TEOS is1mL, at200℃and filling volumes of60%hydrothermal react10h, we received filmwhich was similar to lotus leaf surface. It has bulges in micrometer and some smallnanometer papillae on the bulges with the diameter of0.2μm～0.5μm, height ofapproximately30nm~70nm. The diameter and height of nanoscale roughnessstructures is10nm~30nm and3nm~10nm respectivel. The films changed fromsuperhyrophobilic to superhydrophobic after modified by trimethylchlorosilane, theWCA is up to153.8°. Water droplets on the film surface id agreed with Cassiemodel, through the calculation of composite films when the contact angle of153.8°,the solid surface took up9.73%of the contact area, gas should be accounted for90.27%.The superhydrophobic films through the above method is all consisted of micronano double roughness structures.This multi-level rough structure has unplacedadvantages in the fabrication of superhydrophobic film.The air is enwrappedattributed to the hierarchical structure and became air cushion, so the water dropletssit on the film in the form of “point” to “point”, so the WCA is high and the roll-offangel is small.The films prepared from hydrothermal process must be modified by the lowsurface energy material to achieve superhydrophobic, so the resistance of themodified film is poor. When exposed the silica/alumina composite film to the naturalenvironment, it losed superhydrophobic properties two weeks later and water contactangle becomes147.7°. The WCA of silica/zinc oxide films in the second weekschanged to148.4°.