title: How to explain microemulsions formed by solvent mixtures without conventional surfactants.
abstract: 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 Sci60(3):488-496 and Keiser BA, Varie D, Barden RE, Holt SL (1979)J Phys Chem83(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.
authors.affiliation: ICSM (Institut de Chimie Séparative de Marcoule), UMR 5257 (Commissariat a l'energie atomique et aux energies alternatives/CNRS/Ecole Nationale Supérieure de Chimie de Montpellier, Université de Montpellier), 30207 Bagnols sur Cèze, France; thomas.zemb@icsm.fr Werner.Kunz@chemie.uni-regensburg.de.
authors.forename: Thomas N
authors.initials: TN
authors.lastname: Zemb
authors.affiliation: Institut für Physikalische und Theoretische Chemie, Universität Regensburg, 93053 Regensburg, Germany;
authors.forename: Michael
authors.initials: M
authors.lastname: Klossek
authors.affiliation: ICSM (Institut de Chimie Séparative de Marcoule), UMR 5257 (Commissariat a l'energie atomique et aux energies alternatives/CNRS/Ecole Nationale Supérieure de Chimie de Montpellier, Université de Montpellier), 30207 Bagnols sur Cèze, France; Institut für Physikalische und Theoretische Chemie, Universität Regensburg, 93053 Regensburg, Germany;
authors.forename: Tobias
authors.initials: T
authors.lastname: Lopian
authors.affiliation: Institut für Physikalische und Theoretische Chemie, Universität Regensburg, 93053 Regensburg, Germany;
authors.forename: Julien
authors.initials: J
authors.lastname: Marcus
authors.affiliation: Institut für Physikalische und Theoretische Chemie, Universität Regensburg, 93053 Regensburg, Germany;
authors.forename: Sebastian
authors.initials: S
authors.lastname: Schöettl
authors.affiliation: Institut für Physikalische und Theoretische Chemie, Universität Regensburg, 93053 Regensburg, Germany;
authors.forename: Dominik
authors.initials: D
authors.lastname: Horinek
authors.affiliation: European Synchrotron Radiation Facility (ESRF), 38043 Grenoble, CEDEX 9, France;
authors.forename: Sylvain F
authors.identifier: http://orcid.org/0000-0002-6008-1987
authors.initials: SF
authors.lastname: Prevost
authors.affiliation: Institut für Physikalische und Theoretische Chemie, Universität Regensburg, 93053 Regensburg, Germany;
authors.forename: Didier
authors.initials: D
authors.lastname: Touraud
authors.affiliation: ICSM (Institut de Chimie Séparative de Marcoule), UMR 5257 (Commissariat a l'energie atomique et aux energies alternatives/CNRS/Ecole Nationale Supérieure de Chimie de Montpellier, Université de Montpellier), 30207 Bagnols sur Cèze, France;
authors.forename: Olivier
authors.initials: O
authors.lastname: Diat
authors.affiliation: Department of Applied Mathematics, Research School of Physics & Engineering, Australian National University, Canberra, ACT 0200, Australia.
authors.forename: Stjepan
authors.initials: S
authors.lastname: Marčelja
authors.affiliation: ICSM (Institut de Chimie Séparative de Marcoule), UMR 5257 (Commissariat a l'energie atomique et aux energies alternatives/CNRS/Ecole Nationale Supérieure de Chimie de Montpellier, Université de Montpellier), 30207 Bagnols sur Cèze, France; Institut für Physikalische und Theoretische Chemie, Universität Regensburg, 93053 Regensburg, Germany; thomas.zemb@icsm.fr Werner.Kunz@chemie.uni-regensburg.de.
authors.forename: Werner
authors.initials: W
authors.lastname: Kunz
keywords: aggregation; hydration force; hydrotrope; micelles; microemulsions