Sol–gel preparation of PTMS modified hydrophobic and transparent silica coatings

Wettability of solid surfaces is an important property, which depends on both the surface chemistry and surface roughness. The present paper describes the room temperature synthesis of dip coated water repellent silica coatings on glass substrates using phenyltrimethoxysilane (PTMS) as a co-precursor with two-step sol–gel process. Silica sol was prepared by keeping the molar ratio of tetraethylorthosilicate precursor, methanol solvent, acidic water (0.001 M oxalic acid) and basic water (12 M NH4OH) constant at 1:11.03:0.17:0.58 respectively, throughout the experiments and the PTMS weight percentage was varied from 0 to 15 %. It was found that with an increase in wt% of PTMS, the roughness and hydrophobicity of the films increased. However, the optical transmission decreased from 93 to 82 % in the visible range. The hydrophobic silica films retained their hydrophobicity up to a temperature of 386 °C and above this temperature the films became hydrophilic. The hydrophobic silica thin films were characterized by taking into consideration the surface roughness studies, Fourier transform infrared spectroscopy, percentage of optical transmission, scanning electron microscopy, thermogravimetric–differential thermal analysis and contact angle measurements.