Formation Process of Super‐Water‐Repellent Al ₂ O ₃ Coating Films with High Transparency by the Sol–Gel Method

Abstract

Alumina thin films with a roughness of 20 to 50 nm were formed by immersing porous alumina gel films prepared by the sol‐gel method in boiling water. When hydrolyzed fluoroalkyltrimethoxysilane was coated on the alumina films, the contact angle for water was increased with an increase of immersion time, and immersion for 30 s was long enough to give super‐water‐repellency and high transparency; the contact angle for water of the film was 165° and the transmittance for the visible light was higher than 92%. It was found that the surface of the alumina gel films immersed in boiling water consisted of boehmite crystals. It was shown that the existence of air in the hydrophobic pores on the surface caused the super‐water‐repellency.