An infrared study of micelle formation in AOT-H₂O-CCl₄ solutions

Abstract

The concentration dependence of the infrared spectra of CCl₄ solutions of AOT [bis(2-ethylhexyl)sodium sulfosuccinate] has been determined in a concentration range (0–1.6 mM) encompassing the critical micelle concentration (CMC ≃ 0.2 mM). — Effects detected on the molar extinction coefficients of the bands due to C-H stretching vibrations can be used as indicators of micelle formation. — The same spectroscopic technique has also been used to investigate the structure of water in oil microemulsion. The interaction of water with reversed micelles of AOT has been studied as a function of the ratio W = [H₂O]/[AOT] in the range 0–12 by using the absorption band due to O-H stretching mode, in the 3800–3000 cm⁻¹ range, and the absorption band in the range 1700–1500 cm⁻¹, arising from the H-O-H bending vibration. Our results indicate that at low W values (W < ∼4) the water in micellar core is structurally and motionally different from unperturbed bulk water. On increasing W, water displays more marked "bulk" properties, and the absorption bands approach that of bulk water.