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

Abstract

Five series of novel fluorinated aerogels based on acylated (3-aminopropyl)trimethoxysilane (APTMS) (MeO)₃Si(CH₂)₃NHC(O)R_F (R_F = 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.