title: Interplay of Noncovalent Interactions in Ionic Liquid/Sodium Bis(2-ethylhexyl) Sulfosuccinate Mixtures: From Lamellar to Bicontinuous Cubic Liquid Crystalline Phase.
abstract: Phase transitions in mixtures of imidazolium based ionic liquid ([C12mim]Br) and anionic double tail surfactant, sodium bis(2-ethylhexyl) sulfosuccinate (AOT), were studied using a multitechnique approach. The system was primarily chosen for its expected ability to form a variety of lamellar and nonlamellar liquid crystalline phases which can transform into each other via different mechanisms. Depending on the bulk composition and total surfactant concentration, mixed micelles, coacervates, and lamellar and inverse bicontinuous cubic liquid crystalline phase were observed. Along with electrostatic attractions and geometric packing constraints, additional noncovalent interactions (hydrogen bonding, π-π stacking) enhanced attractive interactions and stabilized low curvature aggregates. At stoichiometric conditions, coexistence of coacervates and vesicles was found at lower, while bicontinuous cubic phase and vesicles were present at higher total surfactant concentrations. The phase transitions from a dispersed lamellar to inverse cubic bicontinuous phase occur as a consequence of charge shielding and closer packing of oppositely charged headgroups followed by a change in bilayer curvature. Transition is continuous with both phases coexisting over a relatively broad range of concentrations and very likely involves a sponge-like phase as a structural intermediate. To the best of our knowledge, this type of phase transition has not been observed before in surface active ionic liquid/surfactant mixtures.
authors.affiliation: Department of Chemistry, Faculty of Science, University of Zagreb , Horvatovac 102a, 10 000 Zagreb, Croatia.|Institute of Complex Systems, Forschungszentrum Jülich , Leo-Brandt Strasse, 52425 Jülich, Germany.
authors.forename: Sanja
authors.initials: S
authors.lastname: Novak
authors.affiliation: Department of Chemistry, Faculty of Science, University of Zagreb , Horvatovac 102a, 10 000 Zagreb, Croatia.
authors.forename: Sara
authors.initials: S
authors.lastname: Morasi Piperčić
authors.affiliation: Department of Chemistry, Faculty of Science, University of Zagreb , Horvatovac 102a, 10 000 Zagreb, Croatia.
authors.forename: Sandro
authors.initials: S
authors.lastname: Makarić
authors.affiliation: Department of Chemistry, Faculty of Science, University of Zagreb , Horvatovac 102a, 10 000 Zagreb, Croatia.
authors.forename: Ines
authors.initials: I
authors.lastname: Primožič
authors.affiliation: Department of Histology and Embryology, University of Zagreb School of Medicine , Šalata 3, 10 000 Zagreb, Croatia.
authors.forename: Marija
authors.initials: M
authors.lastname: Ćurlin
authors.affiliation: Division of Physical Chemistry, Ruđer Bošković Institute , Bijenička cesta 54, 10 000 Zagreb, Croatia.
authors.forename: Zoran
authors.initials: Z
authors.lastname: Štefanić
authors.affiliation: Division of Physical Chemistry, Ruđer Bošković Institute , Bijenička cesta 54, 10 000 Zagreb, Croatia.
authors.forename: Darija
authors.identifier: 0000-0001-5261-5961
authors.initials: D
authors.lastname: Domazet Jurašin