Superhydrophobic Films on Glass Surface Derived from Trimethylsilanized Silica Gel Nanoparticles

The paper deals with the fabrication of sol gel-derived superhydrophobic films on glass based on the macroscopic silica network with surface modification. The fabricated transparent films were composed of a hybrid -Si(CH3)(3)-functionalized SiO2 nanospheres exhibiting the desired micro/nanostructure, water repellency, and antireflection (AR) property. The wavelength selective AR property can be tuned by controlling the physical thickness of the films. Small-angle X-ray scattering (SAXS) studies revealed the existence of SiO2 nanoparticles of average size similar to 9.4 nm in the sols. TEM studies showed presence of interconnected SiO2 NPs of similar to 10 nm in size. The films were formed with uniformly packed SiO2 aggregates as observed by FESEM of film surface. FTIR of the films confirmed presence of glasslike Si-O-Si bonding and methyl functionalization. The hydrophobicity of the surface was depended on the thickness of the deposited films. A critical film thickness (>115 nm) was necessary to obtain the air push effect for superhydrophobicity. Trimethylsilyl functionalization of SiO2 and the surface roughness (rms approximate to 30 nm as observed by AFM) of the films were also contributed toward the high water contact angle (WCA). The coated glass surface showed WCA value of the droplet as high as 168 +/- 3 degrees with 6 mu L of water. These superhydrophobic films were found to be stable up to about 230-240 degrees C as confirmed by TG/DTA studies, and WCA measurements of the films with respect to the heat-treatment temperatures. These high water repellant films can be deposited on relatively large glass surfaces to remove water droplets immediately without any mechanical assistance.