Adsorption of Hexane and Benzene on Fluorinated Silicas: The Effect of the Perfluoralkyl Chain Length
Protection of Metals and Physical Chemistry of Surfaces, 45(2), 152 -157, January 2009
Alexander Y. Fadeev, Ph.D.
Department of Chemistry and Biochemistry
T.M. Roshcina, N.K. Shoniya, A.B. Nikol'skaya & M.S. Lagutova
By means of the gas chromatography and a static adsorption method, the extent of fluorination of the carrier surface, determined by the length of the grafted radical chain, affects the adsorption properties of silicas with perfluorohexyl, perfluoropropyl and trifluoromethyl coatings. The analysis of data on the original carrier and chemically hydrophobized silicas, including a sample with grafted octyl groups used as the reference, shows that modification leads to the decrease in both the adsorption (a at 298 K and the Henry constants (K H ) in a wide temperature range for hexane and benzene. However, in contrast to silicas with perfluoropropyl or perfluorohexyl coatings, the a and K H values on trifluorometylsilica became equal (n-alkanes) or even somewhat lower (aromatic hydrocarbons) than those observed on the non-polar octylsilica surface. Irrespective of the degree of fluorination of the silica surface, the substitution and screening of silanol groups in silica lead to weakening the polarity of polyfluoroalkylsilicas as compared with the original carrier.