Direct syntheses using a fluorinated surfactant of silicas containing organofluorinated groups

Abstract

Direct syntheses of silicas containing organofluorinated groups have been achieved by co-condensation of tetraethylorthosilicate (TEOS) and a organofluorinated triethoxysilane, R_F(CH₂)₂Si(OEt)₃ [R_F = CF₃(CF₂)₅ or CF₃], in the presence of either the neutral fluorinated surfactant n-CF₃(CF₂)₇(CH₂)₂NH₂ or the cationic one, n-CF₃(CF₂)₇(CH₂)₂NMe₃⁺I⁻. Microporous silica with a wormhole structure containing the C₈ fluorinated chain was obtained in the presence of the nonionic surfactant. It was shown that the use of fluorinated surfactants allows the incorporation of an amount of (fluorinated) chains located in the channel pores that is superior to that obtained by using a hydrogenated surfactant. The cationic surfactant used under acidic conditions allowed the incorporation of only a low amount of the C₈ fluorinated chain, leading to a poorly structured material. In contrast, a mesoporous silica containing the CF₃(CH₂)₂ group and showing a hexagonal arrangement was obtained under the same experimental conditions.