An infrared-spectroscopic study of reversed micellar solutions of sodium n-octanoate and water in n-decanol

The association process to reversed micelles in the system water/sodium n-octanoate/n-decanol is studied by means of wave number shifts in the fundamental infrared region. It is found that the antisymmetric vibration band (σ₃), and the scissors vibration band (σ₂) of water, together with the antisymmetric stretching vibration band of the ionised carboxylic groups (σ_COO?) are capable of detecting and visualising changes in the micellar association equilibria. The information is primarily qualitative, but some rough quantitative estimations are also made. A comparison between the intensities of the narrow σ₃-line corresponding to unassociated water OH-oscillators discernible at high dilutions in decanol, and the broad σ₃-band of the associated species reveals that the fraction of unassociated OH-groups in water is low, perhaps only a few percent.