Preparation and properties of fluorinated carboxylic acid/silica nanocomposite-encapsulated low molecular weight compounds

Perfluoro-2-methyl-3-oxahexanoic acid/silica nanocomposites R_F-CO₂H/SiO₂] were prepared by the sol–gel reaction of tetraethoxysilane in the presence of silica nanoparticles and the corresponding fluorinated carboxylic acid under alkaline conditions. R_F-CO₂H/SiO₂ nanocomposites were found to exhibit no weight loss in proportion to the contents of fluorinated carboxylic acid in the composites even after calcination at 800 °C. The modified glass surface treated with the R_F-CO₂H/SiO₂ nanocomposites was shown to give a good oleophobicity with superhydrophilicity imparted by fluorinated carboxylic acid in the composites. R_F-CO₂H/SiO₂ nanocomposites were also applied to the encapsulation of a variety of low molecular weight aromatic and aliphatic compounds such as bisphenol AF BPAF], bisphenol A BPA], 4,4′-biphenol BPOH], octafluoro-4,4′-biphenol FBPOH], 4,4′-bis(triethoxysilyl)-1,1′-biphenyl BTSBP], 3-(trihydroxysilyl)propane-1-sulfonic acid THSP], α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), and γ-cyclodextrin (γ-CD). Encapsulated aromatic compounds possessing acidic hydroxyl groups such as BPAF, BPA, and FBPOH in the R_F-COOH/SiO₂ nanocomposites were found to exhibit no weight loss corresponding to the contents of aromatic compounds in the composites even after calcination at 800 °C. On the other hand, encapsulated aromatic compounds possessing no acidic hydroxyl groups such as BTSBP and aliphatic compounds (THSP, α-, β-, and γ-CD) gave a clear weight loss corresponding to the contents of these compounds in the composites after calcination. In addition, the fluorinated silica nanocomposite-encapsulated these compounds were applied to the surface modification of glass to exhibit a good oleophobicity with superhydrophilicity imparted by fluorinated carboxylic acid on the surface.