Interactions of perfluorinated surfactant with polycyclic aromatic hydrocarbons: Critical micelle concentration and solubility enhancement measurements

Perfluorinated surfactants (PFSs) are characterized by high chemical and thermal stability and are used in a wide range of products and processes. Some current uses of these compounds lead to the releases of persistent fluorocarbons into the environment. The effects of a PFS on the behavior of hydrocarbons such as polycyclic aromatic hydrocarbons (PAHs) are not well understood. This study investigated the PFS-PAH interactions through critical micelle concentration (CMC) and solubility enhancement measurements. An anionic PFS, lithium perfluorooctanesulfonate (LiFOS) and two PAHs (phenanthrene and pyrene) were used. CMC values of LiFOS measured by three different methods fell in the range of 5.5-7.4 mM at 22 +/-1 degreesC, and showed. a small dependence of CMCs on the PAH probe molecules. Mole fraction micellar partition coefficient (K-mic) values were found to be 2.27 x 10(2), 7.74 x 10(3), and 1.25 x 10(4) for oxygen, phenanthrene, and pyrene, respectively, at 22 +/-1 degreesC. Log K-mic values for oxygen and PAHs were linearly correlated with the log values of octanot-water partition coefficients (log Kc,), showing that hydrophobic interactions with LiFOS micelles are favorable enough to increase apparent solubilities across a range of solute hydrophobicities. Overall, PFSs are shown to have less favorable interactions with PAHs because of the restrictions in practically usable chain length with PFS and mutual phobicity between hydrocarbons and fluorocarbons, compared to hydrocarbon surfactants. (C) 2001 Academic Press.