Change of amphiphilic association structures during evaporation from emulsions in surfactant-fragrance-water systems.

The phase diagrams of a nonionic surfactant (Laureth 4), water, and three different fragrance compounds, limonene, phenethyl alcohol and benzaldehyde, were compared. The location of the fragrance molecules in the lamellar liquid crystals (LLC) was investigated using the small-angle X-ray diffraction. The evaporation processes of the fragrance emulsions, consisting of 80 wt.% water, 15 wt.% fragrance and 5 wt.% surfactant, were followed both experimentally through an optical microscope, and theoretically through calculation based on the knowledge of the vapour pressure of the fragrance along the demixing line of the water-in-oil microemulsion (L(2)) phase boundary. Evaporation of the phenethyl alcohol emulsion led the system directly into the L(2) phase region, with very little phenethyl alcohol evaporated in 20 min. For the limonene system, during evaporation the system experienced several multi-phase regions, then reached the water-surfactant axis, and finally went into the L(2) phase region. By contrast to phenethyl alcohol, limonene evaporated completely within 10 min. Benzaldehyde emulsion went through structural changes similar to those of limonene, while the fragrance evaporated continuously until completion in 20 min.