Preparation of biomimetic superhydrophobic silica film by sol-gel technique

A superhydrophobic silica film was prepared by means of sol-gel and self-assembly techniques, with a very high water contact angle (155°-157°) and a small sliding angle (3°-5°), making water droplet move readily on the surface. The film surface morphologies were observed with scanning electron microscope, and the elements on surface were determined by X-ray photoelectron spectroscopy. It was found that there were many microconvexities with binary structure uniformly distributed on the surface atop of the film with the average diameter of about 0.2 μm and nanoconvexities on the lower surface layer of the film with the average diameter of about 13 nm, and the film surface structure was similar to that of lotus surface. Many elements such as F and Cl were observed on the film surface, which could make the film surface energy decreased dramatically. The possible reason of leading to superhydrophobic properties on the as-prepared film is due to form an appropriate surface roughness after sol-gel method, and its surface energy will be further decreased after being modified with perfluorooctyltrichloromethoxysilane (FOTMS). These two formed conditions of surface roughness and low surface energy on the film will make the film formed on silicon exhibit good superhydrophobic properties.