Adsorption of Organic Molecule and Water to Cast Films of Polyfluorinated Cationic Surfactants

Tadatoshi OHMACHI, Hiromi KUSAKA, Shinsuke TAKAGI and Haruo INOUE*

Department of Applied Chemistry, Raduate Course of Engineering, Tokyo Metropolitan University; 1-1 Minamiohsawa, Hachiouji-shi 192-0397 Japan

Vapor phase adsorption behavior of hexane, benzene, ethanol, and water to films of polyfluorinated surfactants, N-methyl-N,N-dioctadecyl(3-perfluoroacylamino)propylammonium bromide having three different number of carbon n=1, 2, 3 in the perfluoroalkyl group, and to films of corresponding three hydrocarbon analogues were studied by quartz crystal microbalance method. The surfactant films were made by casting them on gold plated on quartz crystals. Adsorption-desorption equilibrium constant, number of adsorption site, adsorption rate constant, and desorption rate constant were determined. Nonpolar hexane and benzene were observed to be readily adsorbed and desorbed, while polar ethanol and water had slower adsorption and desorption rate constants. The larger number of adsorption site and the total area of adsorption suggested that polar ethanol and water adsorbed to ammonium and amide groups of the surfactants in a similar mechanism of solvation. The casted films of polyfluorinated surfactants have been suggested to have partly the similar surface polyfluorinated micro-structure with those reported in polyfluorinated micelles and vesicles, while the films of hydrocarbon type surfactants had micro-structure where ammonium groups were directly exposed to gas phase.

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