Ultra-water-repellent surface: fabrication of complicated structure of SiO2 nanoparticles by electrostatic self-assembled films

Ultra-water-repellent surface requires a high surface roughness and low surface energy. We designed surface complicated microstructure of SiO2 nanoparticles by using electrostatic self-assembly process. The films that were prepared by the alternate adsorption of poly(allylamine hydrochloride), SiO2 nanoparticles mixture solution and poly(acrylic acid) on the substrates were very complicated in surface structure. After surface hydrophobic treatment by dichlorodimethylsilane, the film surface showed a contact angle of larger than 160° for water droplets. The value was much larger compared with the contact angle on silicon wafer treated by dichlorodimethylsilane. The difference was strongly dependent on the surface structure. In this paper, we changed deposition conditions to fabricate the water-repellent surfaces with various surface structures by using three types of silica nanoparticles, and we found that the nanoscale structure was very important for the ultra-water-repellency.