A Raman spectroscopy study of micellar structures in ternary systems of water-sodium octanoate-pentanol/decanol

Abstract

Raman spectroscopy has been used in order to study the micellar structure of the systems water-sodium octanoate-pentanol and water-sodium octanote-decano. The C—H and C—C stretching vibration regions have been utilized in the study of both the hydrocarbon chain conformation and the degree of polar/apolar contact. In sodium octanoate solutions there seems to be a successive increase in thetrans-conformation up tocmc, and then thetrans/gauche ratio is fairly constant. Sodium octanoate micelles with solubilized pentanol and decanol were examined by using perdeuterated octanoate and water in order to avoid overlapping in the contributions from each component in the spectra. Both pentanol and decanol have the same effect in reducing the contracts between water and hydrocarbon chains. The chain conformation in the micelles is influenced by incorporation of pentanol in the same way as if the octanoate concentration is increased, whereas on the other side decanol influences thetrans/gauche ratio of the hydrocarbon chains. The inverted micelles, considered to consist of water aggregates in a lipophilic environment, were also examined. The strongest structural effects with ragard to waterhydrocarbon chain contact were seen when the water/soap ratio varied. When the soap content is increased in the pentanol system thetrans-conformation seems to increase, whereas the degree ofgauche-conformation increases when the soap concentration is increased in the decanol system.