Effect of Types of Perfume Compounds on the Hydrophile-Lipophile Balance Temperature

The effect of added perfume compounds (d-limonene (LN), alpha-hexylcinnamic aldehyde (HCA), beta-ionone (IN), benzyl acetate (BA), linalool (LL), geraniol (GL), eugenol (EL), and cis-3-hexenol (HL)) on the three-phase behavior was investigated in water/octaethylene glycol dodecyl ether (C(12)EO(8))/perfume compound systems. The HLB (hydrophile-lipophile balance) temperatures are considerably lower than those of saturated hydrocarbon systems and are in the order LN > HCA > IN > BA > LL > GL > EL > HL. It is considered that the perfume molecules tend to be solubilized in the vicinity of the interface of the water-hydrocarbon moieties of the surfactant or the surfactant palisade layer. To confirm this, the location of the solubilized perfume compound in aggregates of liquid crystals was investigated by small-angle X-ray scattering (SAXS). In the LN, HCA, IN, BA, LL, and GL systems, the hexagonal liquid crystalline phase changes to lamellar liquid crystals on addition of each perfume compound, whereas the hexagonal liquid crystalline phase is directly changed to a reverse micellar solution phase in the EL and HL systems. The effective cross-sectional area per surfactant molecule, a(s), was calculated by using interlayer spacing measured by SAXS. Perfume compounds, which reduce the HLB temperature greatly, tend to penetrate into the surfactant palisade layer and increase a(s). Thus, the perfume molecules change the surfactant curvature from positive to negative. The more the perfume compound penetrates into the palisade layer, the lower the HLB temperature becomes. Copyright 1999 Academic Press.