Ternary solutions containing one hydrotrope (such as ethanol) and two immiscible fluids, both being soluble in the hydrotrope at any proportion, show unexpected solubilization power and allow strange but yet unexplained membrane enzyme activity. We study the system ethanol-water-octanol as a simple model of such kinds of ternary solutions. The stability of "detergentless" micelles or microemulsions in such mixtures was proposed in the pioneering works of Barden and coworkers [Smith GD, Donelan CE, Barden RE (1977) J Colloid Interface Sci 60(3):488-496 and Keiser BA, Varie D, Barden RE, Holt SL (1979) J Phys Chem 83(10):1276-1281] in the 1970s and then, neglected, because no general explanation for the observations was available. Recent direct microstructural evidence by light, X-ray, and neutron scattering using contrast variation reopened the debate. We propose here a general principle for solubilization without conventional surfactants: the balance between hydration force and entropy. This balance explains the stability of microemulsions in homogeneous ternary mixtures based on cosolvents.A dding slightly hydrophobic compounds to water can lead to structureless solutions, aggregate formation, or even, formation of defined structures, such as micelles, in the case where the added compound is a surfactant. In ternary or quaternary mixtures containing at least one type of surfactant, the formation of microemulsions usually occurs in specific parts of the phase diagram. These macroscopically homogeneous, transparent liquids are composed of well-defined microstructures with specific signatures in scattering experiments (1). It was only recently that similar structures, designated as "pre-Ouzo," were found and characterized in ternary mixtures of two partly miscible solvents and one hydrotropic cosolvent (2). In this paper, we present a theory that explains and even predicts the existence of such structures in "detergentless" formulations.Ouzo, Limoncello, and Pommeau liquors are popular in several European countries and produced by maceration of plants with a specific amount of ethanolic solutions containing some waterinsoluble compounds (3). Adding water to those solutions leads to spontaneous formation of fine emulsions with a remarkable stability, a phenomenon that is called the "Ouzo effect" (4). Even common mouthwash products show a similar phenomenon. In common, they entirely clear up on addition of ethanol and get milky with the addition of water (5).Ternary surfactant-free model systems, such as decane-waterisobutoxyethanol [as studied by Shinoda and Kunieda (6)], however, show this Ouzo effect only for specific points in the composition diagram. The precondition for such behavior seems to be the mixture of two miscible (either completely or at least to a large degree) solvents 1 and 2 with a solute that can also be a liquid (7) (e.g., anethole in the case of Ouzo; component 3). This component 3 must be highly soluble in one solvent (e.g., ethanol) but poorly soluble in the other one (e.g., water) (8).Where...

Ternary mixtures of medium-chain fatty alcohols, water and a hydrotrope (such as ethanol), near the immiscibility gap, make stable single phases at constant temperature. Interestingly, in this 'pre-ouzo region' these single phases consist of two distinct nanoscopic pseudo-phases, one octanol-rich and one water-rich. This domain of composition, which is known to produce strong light scattering and to separate under ultracentrifugation into two phases, has been studied using contrast variation in small-angle neutron scattering (SANS) combined with small-and wide-angle X-ray scattering (SWAXS). The existence of fatty alcohol-rich domains of well defined size of the order of 2 nm radius is proven. The scattering can be approximated by an Ornstein-Zernike function, which is close to the general expression of Choi, Chen, Sottmann & Strey [Physica B, (1998), 241-243, 976-978] with vanishing quadratic Porod term. Exploitation of the relative intensities at the vanishing scattering angle in SANS demonstrates that the distribution coefficient of ethanol between the octanol-rich and the water-rich domains is close to one. WAXS of the two coexisting pseudo-phases is compared with the corresponding binary water-ethanol and octanol-ethanol samples.

Cheers! The combination of static and dynamic light scattering is demonstrated to deliver an unambiguous proof that well-defined domains of two fluids of clearly different composition can exist in surfactant-free ternary mixtures (see picture for diagram), such as Ouzo.

In this paper we consider clusters in the ternary systems water-benzyl alcohol and ethanol, ethyl lactate or g-valerolactone as found with the help of dynamic and static light scattering experiments. These ternary mixtures are powerful solvent media and consist only of low-toxic solvents of natural origin. In a recent work we have shown that surfactantless microemulsions are formed in the water-ethanol-noctanol system. By contrast, in the systems studied here the sizes of the aggregates are too small to be considered as micelles. It can be postulated that the presence of clusters or larger structures as in surfactantless microemulsions is strongly influenced by the most hydrophobic compound. The phenomenon of facilitated hydrotropy is also investigated in the above-mentioned systems. In this context, ethanol is considered as the primary hydrotrope and the more hydrophobic benzyl alcohol as the facilitating secondary hydrotrope. The hydrophobic dye Disperse Red 13 is used as a marker of facilitated hydrotropy.The results suggest that the degree of self-association of eco-solvent has a significant influence on the hydrotropic efficiency of benzyl alcohol.

Recently it was shown that water–ethanol–long‐chain alcohol mixtures can be significantly structured in a wide range of compositions. This work is an extension of these studies and suggests that some formulated products on the market correspond to these mixtures. We consider the domains of existence of the clear and homogeneous phase of four water–ethanol–perfumery molecules systems, the perfumery molecules being citronellol, citral, geranyl acetate and limonene, as they can be found in perfumery formulations. Dynamic and static light scattering experiments reveal also the presence of nano‐droplets in these ternary tincture systems. Based on these results the presence of nano‐droplets can be expected in Eau de Toilette, Eau de Parfum, and possibly in perfumes. Copyright © 2013 John Wiley & Sons, Ltd.