Partitioning and Localization of Fragrances in Surfactant Mixed Micelles

Abstract

The localization and dynamics of fragrance compounds in surfactant micelles are studied systematically in dependence on the hydrophobicity and chemical structure of the molecules. A broad range of fragrance molecules varying in octanol/water partition coefficients P ow is employed as probe molecules in an aqueous micellar solution, containing anionic and nonionic surfactants. Diffusion coefficients of surfactants and fragrances obtained by Pulsed Field Gradient (PFG)-NMR yield the micelle/water distribution equilibrium. Three distinct regions along the log(P ow ) axis are identified: hydrophilic fragrances (log(P ow ) \ 2) distribute almost equally between micellar and aqueous phases whereas hydrophobic fragrances (log(P ow ) [ 3.5) are fully solubilized in the micelles. A steep increase of the incorporated fraction occurs in the intermediate log(P ow ) region. Here, distinct micelle swelling is found, while the incorporation of very hydrophobic fragrances does not lead to swelling. The chemical structure of the probe molecules, in addition to hydrophobicity, influences fragrance partitioning and micelle swelling. Structural criteria causing a decrease of the aggregate curvature (flattening) are identified. 2 H-NMR spin relaxation experiments of selectively deuterated fragrances are performed monitoring local mobility of fragrance and leading to conclusions about their incorporation into either micellar interface or micelle core. The tendencies of different fragrance molecules (i) to cause interfacial incorporation, (ii) to lead to a flattening of the micellar curvature and (iii) to incorporate into micelles are shown to be correlated.

Enhanced perfume surface delivery to interfaces using surfactant surface multilayer structures

“…This is consistent with previous observations from the surface adsorption of surfactant/perfume mixtures [30] and on the impact of perfumes on surfactant self-assembly [9,26,[36][37][38]. Furthermore, the variation in the scattering length densities of both the alkyl chain and headgroup regions, for d-LAS-6/h-perfume and h-LAS-6/d-perfume, is consistent with that interpretation.…”

“…The more hydrophilic phenylethanol is predominantly solubilized into the headgroup region. These different locations are consistent with the observations associated with surfactant self-assembly and perfume solubilization [9,26,35]. The differences in location result in the surface multilayer structures existing over a wider range of surfactant/perfume compositions for phenylethanol than for linalool.…”

“…4 for 70/30 mol ratio LAS-6/PE. It has previously been demonstrated at the interface [30] and in solution [9,11] that the more hydrophilic phenylethanol is preferentially located close to the headgroup region. Hence in the modeling of the data here it is assumed that the phenylethanol is in the region of the bilayer (d 2 ) occupied by the phenyl ring and headgroup.…”

“…A wide range of model perfume molecules with differing degrees of solubility and hydrophobicity have been studied, and include fragrance components such as phenyl ethanol, limonene, linalool, geraniol and eugenol. These studies have largely focused on aspects such as the solubilization in different surfactant systems [4][5][6][7][8], the location of the perfume molecule within the self-assembled structure [9], and their impact upon surfactant phase behavior [10][11][12]. In contrast there have been relatively few studies which have directly probed the co-adsorption of perfumes with surfactants at interfaces, or investigations in which the adsorption can be enhanced.…”

Classification of Fragrances and Fragrance Mixtures Based on Interfacial Solubilization

“…In fact, very hydrophobic molecules are located at the interior of the micellar core, whereas linear primary alcohols possess an amphiphilic character and can insert themselves into the interface of the surfactant palisade layer [5][6][7]. For example, it has been shown that a terpenic alcohol leads to micellar swelling in an all purpose cleaner formulation, which is a direct consequence of the chemical structure of the molecule and cannot be explained by the log P value [8].…”