Facile preparation and application of fluoroalkyl end-capped vinyltrimethoxysilane oligomer/methyltrimethoxysilane nanocomposite lipogels possessing superoleophilic/superhydrophobic characteristic

Abstract

Two fluoroalkyl end-capped vinyltrimethoxysilane oligomer/methyltrimethoxysilane nanocomposites [RF-(VM-SiO3/2)n-RF/MeSiO3/2] were prepared through the acid-base sol-gel reactions of the corresponding fluorinated oligomer [RF-(CH2-CHSi(OMe)3)n-RF: n = 2, 3; RF = CF(CF3)OC3F7: RF-(VM)n-RF] and methyltrimethoxysilane [MeSi(OMe)3: MTMS] under acidic (acetic acid) and successively under alkaline (ammonium carbonate or aqueous ammonia) conditions. FE-SEM (field emission scanning electron micrographs) measurements showed that the RF-(VM-SiO3/2)n-RF/MeSiO3/2 nanocomposites thus obtained consist of clear monolithic structures, affording a lower bulk specific gravity value (~ 0.06 g/cm3) than that (0.49 g/cm3) of the corresponding original RF-(VM-SiO3/2)n-RF oligomeric nanoparticles, which were prepared in the absence of MTMS under similar acid-base sol-gel conditions. Interestingly, the obtained monolithic fluorinated oligomeric silica nanocomposite powders were found to form the corresponding lipogels toward the traditional organic media, such as methanol, ethanol, 2-propanol (IPA), tetrahydrofuran (THF), 1,2-dichloroethane (DE), N,N-dimethylformamide (DMF), and ethyl isopropyl sulfone except for water. It was demonstrated that the RF-(VM-SiO3/2)n-RF/MeSiO3/2 nanocomposite lipogels can provide a superoleophilic/superhydrophobic characteristic on the modified glass surface, although the corresponding RF-(VM-SiO3/2)n-RF oligomeric nanoparticles afforded an oleophobic/superhydrophobic property on the surface. Such unique surface wettability enabled these fluorinated nanocomposite lipogels to apply to not only the packing material for the column chromatography to separate the water-in-oil (W/O) emulsions but also the selective adsorbent for the fluorinated organic aromatic compounds from aqueous methanol solution.