Classification of Fragrances and Fragrance Mixtures Based on Interfacial Solubilization

In the present study, the influence of perfumes on the interfacial curvature of microemulsions is investigated. The hydrophilic-lipophilic deviation (HLD) concept was applied to nonionic Winsor I type systems (O/W microemulsions in equilibrium with an oil excess phase) containing a mixture of oils with isopropyl myristate as supporting oil and a variety of liquid solutes as co-oil for which an Equivalent Alkane Carbon Number of the mixture (EACN(mix)) was defined. Temperature was used as a formulation variable and the phase inversion temperature change, provoked by the solubilization of different solutes, was determined. The hydrodynamic radius of the droplet and the interfacial solubilization of fragrances were measured subsequently and correlated to the EACN(mix). In a first step, selected perfumery raw materials (PRMs) were used as solutes and were studied separately. It was demonstrated that the PRMs can be classified in interfacial solubility according to their chemical functionalities and they follow the order alcohols > aldehydes > terpenes > aromatics > alkanes. Solutes that lead to low EACN(mix) values (< 6) have preferential interfacial solubility and provoke strong curvature changes, whereas those leading to higher EACN values (> 6) typically do not change the curvature significantly. The HLD method was also applied to complex fragrances and it was demonstrated that they can be considered as single, non-polar entities, and studied as such instead of investigating each raw material included in the composition separately. Determination of the dimensionless number EACN(mix) offers the possibility of classifying perfumes in an environment similar to surfactant formulations of typical consumer products and to predict the interaction with the surfactant base according to the rules established on the basis of the individual raw materials.