title: Influence of additives on the structure of surfactant-free microemulsions.
abstract: We study the addition of electrolytes to surfactant-free microemulsions in the domain where polydisperse pre-Ouzo aggregates are present. As in previous studies, the microemulsion is the ternary system water/ethanol/1-octanol, where ethanol acts as co-solvent. Addition of electrolytes modifies the static X-ray and neutron scattering, and dynamic light scattering patterns, as well as the position of the miscibility gap, where spontaneous emulsification occurs upon dilution with water. All observations can be rationalized considering that electrolytes are either "salting out" the ethanol, which is the main component of the interface stabilizing the aggregates, or producing charge separation via the antagonistic ion effect discovered by Onuki et al. Amphiphilic electrolytes, such as sodium dodecylsulfate or sodium dietheylhexylphosphate, induce a gradual transition towards monodisperse ionic micelles with their characteristic broad scattering "peak". In these micelles the ethanol plays then the role of a cosurfactant. Dynamic light scattering can only be understood by combination of fluctuations of aggregate concentration due to the vicinity of a critical point and in-out fluctuations of ethanol.
authors.affiliation: Institute of Physical and Theoretical Chemistry, University of Regensburg, 93040 Regensburg, Germany. werner.kunz@ur.de.
authors.forename: J
authors.initials: J
authors.lastname: Marcus
authors.affiliation: Institute of Physical and Theoretical Chemistry, University of Regensburg, 93040 Regensburg, Germany. werner.kunz@ur.de.
authors.forename: D
authors.initials: D
authors.lastname: Touraud
authors.affiliation: ESRF, The European Synchrotron, 71 avenue des Martyrs, 38000 Grenoble, France.
authors.forename: S
authors.initials: S
authors.lastname: Prévost
authors.affiliation: Institut de Chimie Séparative de Marcoule, UMR 5257 (CEA/CNRS/UM/ENSCM), 30207 Bagnols sur Cèze, France.
authors.forename: O
authors.initials: O
authors.lastname: Diat
authors.affiliation: Institut de Chimie Séparative de Marcoule, UMR 5257 (CEA/CNRS/UM/ENSCM), 30207 Bagnols sur Cèze, France.
authors.forename: T
authors.initials: T
authors.lastname: Zemb
authors.affiliation: Institute of Physical and Theoretical Chemistry, University of Regensburg, 93040 Regensburg, Germany. werner.kunz@ur.de.
authors.forename: W
authors.initials: W
authors.lastname: Kunz