Solubilization of polycyclic aromatic hydrocarbons in C16E7 nonionic surfactant solutions

Abstract Polycyclic aromatic hydrocarbons (PAHs), namely, naphthalene, phenanthrene, and pyrene, were solubilized in nonionic surfactant micelles formed from heptaoxyethylene monohexadecyl ether (C 16 E 7 ). The sizes of the PAH-incorporated micelles, and the location of the solubilized molecules, were studied using dynamic light scattering, transmission electron microscopy (TEM), and 1 H nuclear magnetic resonance (NMR) spectroscopy. The solubilization of the PAHs increased significantly above a C 16 E 7 concentration of 1 mM, which corresponded to the point at which the morphology of the micelles changed from globular to string-like, as demonstrated by TEM imaging. The string-like micelles then grew with increasing incorporation of PAHs (naphthalene, phenanthrene, and pyrene). The 1 H NMR chemical shifts of the discrete groups of the C 16 E 7 micelles shifted upfield with increasing naphthalene concentration as a result of the ring current and/or local anisotropic effects of the PAH. The 1 H peak of the oxyethylene segment at 3.7 ppm clearly split with increasing naphthalene concentration in the C 16 E 7 solution. The rotating frame nuclear Overhauser and exchange spectroscopy of naphthalene solubilized in C 16 E 7 micelles showed a cross peak between the oxyethylene segment and the 1 H naphthalene peaks. The NMR spectral measurements showed that the solubilized naphthalene molecules were located in the palisade region of the micelles rather than in the core.