FT-IR Study of Ester Solubilization into a Micelle Solution

The existence of phenyl acetate and benzyl acetate solubilized into a sodium decanoate micelle solution was studied by Fourier transform infrared spectroscopy. When the spectra of acetates in a micelle solution are compared with those in CCl4, the νC=O and νasC-O regions of acetates in the micelle solution show great changes, such as band splitting, lower peak shifts, and band broadening. The lower shifts and the band broadening of νC=O indicate that acetates are solubilized into the surface polar layer of the micelle and are affected by hydrogen bonding. The solubilized volume of acetates in the micelle solution was varied, and the dependence of the peak position and the intensity of the νC-O region was examined. Assuming that the peak position represents the environment of the carbonyl group, there are two kinds of environments around the acetates. Most of acetates are in a polar environment, but when the acetates in the micelle come close to saturation, some of them are in a nonpolar environment. The νasC-O region of benzyl acetate in a micelle solution shows a complex band shape, compared with that of phenyl acetate. The asymmetric C-O mode is a skeleton mode and is sensitive to conformational changes. The polar environment around benzyl acetate may make conformational changes in the benzyl acetate.