Experimental Evidence for Random Surface Structures in Dilute Surfactant Solutions

Gazeau, D.; Bellocq, A. M.; Roux, D.; Zemb, Thomas

doi:10.1209/0295-5075/9/5/007

Cited by 124 publications

(98 citation statements)

References 18 publications

(3 reference statements)

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“…This microstructure corresponds to the IUPAC definition of microemulsions, because two immiscible fluids are separated by an interface, which in the case described here, is a nanometerthick diffuse film composed mainly of ethanol (23). However, no "Porod limit" or broad peak characteristic of classical microemulsions is observed (24,25).…”

supporting

confidence: 52%

How to explain microemulsions formed by solvent mixtures without conventional surfactants

Zemb

Klossek

Lopian

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

181

200

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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...

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supporting

confidence: 52%

How to explain microemulsions formed by solvent mixtures without conventional surfactants

Zemb

Klossek

Lopian

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

181

200

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“…where δ is the bilayer thickness and α a geometrical factor whose value is in the range 1.4-1.6 [4,[13][14][15]. With these values we can predict a bilayer thickness in the range 23 Å < δ < 27 Å for the samples of Fig.…”

Section: Saxs Resultsmentioning

confidence: 91%

The sponge phase of a mixed surfactant system

Maldonado

Ober

Gulik-Krzywicki

et al. 2007

Journal of Colloid and Interface Science

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“…[8][9][10] Our observations require only that as the average molecular weight is decreased, at constant surfactant weight content, the high curvature at the micelles decreases and the large aqueous droplet size decreases. The substantially higher hydrophilicity of the MW 750 surfactant at higher concentrations causes a cessation of emulsion formation, and sponge L 3 phases (or at other water concentrations other planar bilayer phases) are then formed.…”

Section: Discussionmentioning

confidence: 99%

Structure of High Internal Phase Aqueous-in-Oil Emulsions and Related Inverse Micelle Solutions. 3. Variation of Surfactant

et al. 2009

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The small angle neutron scattering from high internal phase water-in-hexadecane and saturated ammonium nitrate-in-hexadecane emulsions is compared with that from related hexadecane-based inverse micellar solutions. Three molecular weights of the monodisperse polyisobutylene acid amide (PIBSA) surfactant 750, 1200, and 1700 were studied over a range of surfactant concentrations. As an additional comparison, emulsions based on sorbitan monooleate and isostearate surfactants were investigated. The scattering from molecular weight 1200 water-based PIBSA emulsions can be fitted at all concentrations to a model with a surfactant coated aqueous droplet-oil interface together with the majority of the surfactant in the oil phase of the emulsion in the form of inverse micelles. Variation of the molecular weight shows a variety of phases of increasing curvature: lamellar, sponge, and, most commonly, the emulsion structure described above. In addition, the molecular weight affects the oil component in the emulsions, which can contain either cylindrical micelles or spherical micelles of varying water but constant hexadecane content. Increased phase curvature is favored by both increased PIBSA molecular weight and ammonium nitrate dissolved in the water. These observations are consistent with "Wedge theory". The structures observed in the emulsions are close to those observed in related inverse micellar solutions made from hexadecane, the surfactant, and water. Lower concentrations of surfactant in the micellar solutions decrease micelle curvature, except where the inverse micelles are spherical and small; here, there is little effect of dilution. Substitution of sorbitan surfactants for PIBSAs produces slightly less organized but similar structures, with smaller spherical micelles containing proportionally more water. The aqueous-oil droplet interface has a relatively invariant monolayer of adsorbed surfactant. For all emulsions, we can infer from the mass balance that micelle concentrations are depressed in the inverse micellar solutions because up to half the added surfactant is present as individually dissolved molecules.

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Experimental Evidence for Random Surface Structures in Dilute Surfactant Solutions

Cited by 124 publications

References 18 publications

How to explain microemulsions formed by solvent mixtures without conventional surfactants

How to explain microemulsions formed by solvent mixtures without conventional surfactants

The sponge phase of a mixed surfactant system

Structure of High Internal Phase Aqueous-in-Oil Emulsions and Related Inverse Micelle Solutions. 3. Variation of Surfactant

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