The effect of surface chemistry on anti-soiling properties of transparent perfluoroalkyl and alkyl modified silica coatings

Various physical and chemical surface parameters, e.g., surface roughness and surface chemistry, contribute to anti-soiling (AS) properties. Nevertheless, the effect of surface chemistry has not been distinctly elucidated yet. In this study, a set of mechanically stable and durable hydrophobic AS coatings with controlled surface chemistry were synthesized, while surface roughness was kept below 1 nm. Fluoroalkylsilane (FAS), alkylsilane (AL), and tetraethyl orthosilicate (TEOS) were employed for synthesis. Surface chemistry and surface roughness were quantified by XPS and AFM. A soiling lab simulator was designed to accelerate the soiling process. AS properties were quantified by UV–vis spectroscopy and optical microscopy. The surface free energy of coatings was estimated through (polar and apolar liquids) contact angle measurements (ranging from 16 to 30 mN/m), and a clear correlation was discovered between the AS properties and surface free energy. Moreover, mechanical properties and weathering resistance of the coatings were analyzed by nano-indentation and QUV accelerated weathering tester. While all coatings showed acceptable AS properties (transmission loss after dust deposition between 1/5 and 2/5 of uncoated glass) and excellent mechanical strength (above 27 GPa modulus and 2 GPa hardness), FAS-based coatings showed a significantly higher durability against weathering as compared to the AL-based ones.