Porous superhydrophobic silica films by sol-gel process

Wettability of solid surfaces is a crucial concern in our daily life as well as in engineering and science. The present research work describes the room temperature synthesis of adherent and porous superhydrophobic silica films on glass substrates using methyltriethoxysilane (MTES) as hydrophobic reagent by sol-gel process. The coating sol was prepared by keeping the molar ratio of tetraethoxysilane (TEOS), methanol (MeOH), water (H₂O) constant at 1:22.09:6.25, respectively, with 0.01 M NH₄F catalyst throughout the experiments and the MTES/TEOS molar ratio (M) was varied from 0 to 0.43. The static water contact angle as high as 160° and water sliding angle as low as 3° was obtained for silica film prepared from M = 0.43. The surface morphological study showed the porous structure with pore sizes ranging from 250 to 300 nm. The superhydrophobic silica films retained their superhydrophobicity up to a temperature of 290 °C and above this temperature the films became superhydrophilic. The prepared silica films were characterized by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Fourier Transform Infrared (FT-IR) spectroscopy, percentage of optical transmission, humidity test and static and dynamic water contact angle measurements.