title: Small-angle scattering and morphologies of ultra-flexible microemulsions.
abstract: The phase diagrams of ternary mixtures of partly miscible solvents containing a hydrotropic co-solvent exhibit a variable miscibility gap and one critical point. This work investigates the entire monophasic region far from and near to the miscibility gap in octan-1-ol/ethanol/water, for which ultra-flexible micro-emulsions (UFMEs) are observed by small-angle scattering techniques. SWAXS (combined small- and wide-angle X-ray scattering) allows the elucidation of these types of structure. Three distinct areas can be identified in the phase diagram, with scattering data resembling those from direct, bicontinuous and reverse local structures. These UFMEs are far more polydisperse than their surfactant-based counterparts. Water-rich and solvent-rich domains are only delimited by a small excess of hydrotrope, instead of a well defined surfactant layer of fixed area per molecule. It is shown that all scattering spectra obtained for the nanostructured compositions can be modelled by a simple unified analytical model composed of two uncorrelated contributions. The main one is the Ornstein-Zernike formula for composition fluctuations which gives information about the pseudo-phase domain size. The second is a Lorentzian that captures the structure of at least one of the coexisting pseudo-phases. No Porod law can be measured in the SAXS domain. The proposed expression gives access to two characteristic sizes as well as one inter-aggregate distance.
authors.affiliation: ESRF - The European Synchrotron, 71 avenue des Martyrs, 38000 Grenoble, France.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Prevost
authors.affiliation: Institut de Chimie Séparative de Marcoule (ICSM), UMR 5257 (CEA/CNRS/UM2/ENCSM), 30207 Bagnols-sur-Cèze, France; Institute of Physical and Theoretical Chemistry, University of Regensburg, 93040 Regensburg, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Lopian
authors.affiliation: Institut de Chimie Séparative de Marcoule (ICSM), UMR 5257 (CEA/CNRS/UM2/ENCSM), 30207 Bagnols-sur-Cèze, France; Institute of Physical and Theoretical Chemistry, University of Regensburg, 93040 Regensburg, Germany.
authors.forename: Maximilian
authors.initials: M
authors.lastname: Pleines
authors.affiliation: Institut de Chimie Séparative de Marcoule (ICSM), UMR 5257 (CEA/CNRS/UM2/ENCSM), 30207 Bagnols-sur-Cèze, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Diat
authors.affiliation: Institut de Chimie Séparative de Marcoule (ICSM), UMR 5257 (CEA/CNRS/UM2/ENCSM), 30207 Bagnols-sur-Cèze, France.
authors.forename: Thomas
authors.initials: T
authors.lastname: Zemb
keywords: mesoscale solubilization; small-angle scattering (SAS); surfactant-free microemulsions; ternary phase diagrams; ultra-flexible microemulsions