| Abstract
| - The microenvironments of a series of polyfluorinated surfactants [CnF2n+1CONH(CH2)2N+(CH3)2C16H33Br-; designated as CnF−S, where n = 1−3]/clay (saponite) hybrid compounds dispersed in water-saturatedbenzene were investigated based on the photochemical behavior of Rose Bengal (RB) as a probe molecule.A small-angle X-ray scattering study showed that the interlayer distance (clearance space) of the C3F−S/clay hybrid compounds was expanded up to 3.8 nm by the dispersion in water-saturated benzene fromthe original distance of 3.0 nm for the dried hybrid compound, indicating expansion of the hybrid compoundupon swelling with the solvent benzene. The RB molecules are proposed to form ion-association complexeswith the CnF−S surfactant, most likely existing in the vicinity of the ammonium group of the surfactantintercalated in the cation-exchangeable clay saponite. The absorption and fluorescence maxima of RBintercalated in the hybrid compounds were significantly red-shifted from those in aqueous solution. Thehybrid compounds provide an environment with polarity between that of ethyl acetate and 1-butanol. Themicroscopic polarity of the hybrid compounds depends on the fluorocarbon chain length (n) of the surfactant,and the polarities increase with increasing fluorocarbon chain length. On the basis of the observedphotochemical behavior of RB, including the relative decomposition rates, excited triplet lifetimes, andrelative excited triplet quantum yields, the microscopic concentration of water in the hybrid layer wasestimated to decrease in the order C3F−S > C2F−S > C1F−S. These differences are discussed in relationto differences in the microscopic orientational structure of the polyfluorinated surfactant within the claylayer.
|
