Enhancement of Pigments Hydrophobicity by Mixing with Cr Doped SiO2 Nanoparticles

In this paper, pure and Cr-doped SiO2 was prepared by sol-gel method and deposited on glass substrates by dip-coating and calcination of the resulting thin films at 500 °C. An X-ray diffraction examination was performed for the pure and doped films, where we note the appearance of a spectrum in the form of a wide band at the equivalent Bragg angle at 2θ = 22.6°, which indicates that the obtained material is amorphous silica. After that, field emission scanning electron microscopy was conducted to study the morphology of the pure SiO2 thin layer doped with chromium, as it appears that the prepared film is of good quality and free of cracks and holes, as we note that the crystals adopted certain geometric shapes with different sizes and shapes. Likewise, the particle distribution is uniform with the spherical shape. By examining the atomic force microscope to study the surface topography and roughness, we notice that the surface roughness increases with the increase in the doping percentage, where the surface roughness values ​​of the samples vary between (2.94-5.22) nm, and we will get the highest surface roughness values ​​at a concentration of 9%. After preparing the SiO2 nanoparticles, they are mixed with the pigment and deposited on the glass substrates using the dip-coating method to measure the contact angles and study the duration of the effect of SiO2 particles on the pigment. In addition, by measuring the contact angle between a drop of water and the coating surface, we notice that the contact angle increases after adjusting the coating by adding pure SiO2 doped with chromium and mixed with the pigment, as the contact angle increases from (95.71°) to (107.17°) depending on the surface roughness. The surface roughness and its energy are important factors affecting the contact angle.