SiO2 aerogels modified by perfluoro acid amides: a precisely controlled hydrophobicity

Five series of novel fluorinated aerogels based on acylated (3-aminopropyl)trimethoxysilane (APTMS) (MeO)3Si(CH2)3NHC(O)RF (RF = CF3, C2F5, CF3CF(OCH3), C6F13 and C8F17) were prepared by a sol–gel method followed by supercritical drying in four different solvents, including isopropanol, CO2, methyl tert-butyl ether (MTBE) and hexafluoroisopropyl alcohol (HFIP). The hydrophobicity of the aerogels was shown to increase smoothly with the increase in the length of the fluorinated substituent – the water drop contact angle θ changed from 0° and reached 143° for isopropanol dried samples, 133° for CO2 dried samples, 136° for MTBE dried samples, and ∼140° for HFIP dried samples. The results obtained provide an easy method for the preparation of aerogels with precisely controlled hydrophobicity.