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

Abstract

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.