engleski

Interplay of Noncovalent Interactions in Ionic Liquid/Sodium Bis(2-ethylhexyl) Sulfosuccinate Mixtures : From Lamellar to Bicontinuous Cubic Liquid Crystalline Phase

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 multi-technique approach. The system was primarily chosen for expected ability to form variety of lamellar and non-lamellar liquid crystalline phases which can transform into each other via different mechanisms. Depending on the bulk composition and total surfactant concentration, mixed micelles, coacervates, lamellar and inverse bicontinuous cubic liquid crystalline phase were observed. Along with electrostatic attractions and geometric packing constraints additional non-covalent 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 occurs as a consequence of charge shielding and closer packing of oppositely charged head groups followed by a change in bilayers curvature. Transition is continuous with both phases coexisting over a relatively broad range of concentrations and very likely involves sponge-like phase as structural intermediate. To the best of our knowledge this type of phase transitions has not been observed before in surface active ionic liquid/surfactant mixtures.

non-covalent interactions ; phase transitions ; catanionic mixtures ; vesicles ; coacervates ; cubic bicontinuous phase

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