The Influence of New Hydrophobic Silica Nanoparticles on the Surface Properties of the Films Obtained from Bilayer Hybrids

Ultra-hydrophobic bilayer coatings on a glass surface were fabricated by sol–gel process using hexadecyltrimethoxysilane (C(16)TMS) and tetramethoxysilane (TMOS) (1:4 molar ratio) as precursors. After coating, silica nanoparticles (SiO(2) NPs) functionalized with different mono-alkoxy derivatives (methoxytrimethylsilane, TMeMS; ethoxydimethylvinylsilane, DMeVES; ethoxydimethylphenylsilane, DMePhES; and methoxydimethyloctylsilane, DMeC(8)MS) were added, assuring the microscale roughness on the glass surface. Influences of the functionalized SiO(2) NPs and surface morphology on the hydrophobicity of the hybrid films were discussed. The successful functionalization of SiO(2) NPs with hydrophobic alkyl groups were confirmed by Fourier transform infrared spectroscopy (FTIR). The thermal stability of hydrophobic SiO(2) NPs showed that the degradation of the alkyl groups takes place in the 200–400 °C range. Bilayer coating with C(16)TMS/TMOS and SiO(2) NPs modified with alkoxysilane substituted with C(8) alkyl chain (SiO(2) NP-C(8)) has micro/nano structure. Hydrophobicity of functionalized SiO(2) NPs-C(8) and its higher degree of nanometer-scale roughness gave rise to ultra-hydrophobicity performance for bilayer coating C(16)TMS/TMOS + SiO(2) NPs-C(8) (145°), compared to other similar hybrid structures. Our synthesis method for the functionalization of SiO(2) NPs is useful for the modification of surface polarity and roughness.