title: Self-assembly in a catanionic mixture with an aminoacid-derived surfactant: from mixed micelles to spontaneous vesicles.
abstract: The aqueous self-assembly of a novel lysine-derived surfactant with a gemini-like architecture, designated here as 12-Lys-12, has been experimentally investigated for the amphiphile alone in water and in a mixture with dodecyltrimethylammonium bromide (DTAB). The neat surfactant forms interesting micrometer-sized rigid tubules in the dilute region, resulting in very viscous solutions. For the catanionic mixture with DTAB, various single and multiphase regions were identified (up to a total surfactant concentration of 1.5 wt %) by means of combined polarizing light microscopy, cryo-TEM, and NMR. In the DTAB-rich side, for a mixing molar ratio in the range 2 < DTAB/12-Lys-12 < 4, a region of stable, unilamellar vesicles can be found. Furthermore, it was found that upon addition of 12-Lys-12 to pure DTAB solutions, the mixed micelles grow and beyond a given mixing ratio, vesicles assemble and coexist with small micelles. The transition is not continuous, since there is a narrow mixing range where phase separation occurs. Self-diffusion measurements and cryo-TEM imaging show that the average vesicle radius is on the order of 30-40 nm.
authors.affiliation: Centro de Investigação em Química, Department of Chemistry, Faculty of Sciences, University of Porto, Rua do Campo Alegre No. 687, P-4169-007 Porto, Portugal.
authors.forename: Rodrigo O
authors.initials: RO
authors.lastname: Brito
authors.forename: Eduardo F
authors.initials: EF
authors.lastname: Marques
authors.forename: Paula
authors.initials: P
authors.lastname: Gomes
authors.forename: Soraia
authors.initials: S
authors.lastname: Falcão
authors.forename: Olle
authors.initials: O
authors.lastname: Söderman
mesh_terms: D000838:Anions; D002152:Calorimetry, Differential Scanning; D002412:Cations; D002627:Chemistry, Physical / Q000379:methods*; D020285:Cryoelectron Microscopy; D004058:Diffusion; D008239:Lysine / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008853:Microscopy; D046529:Microscopy, Electron, Transmission; D008956:Models, Chemical; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D013499:Surface Properties; D013501:Surface-Active Agents / Q000737:chemistry; D014867:Water / Q000737:chemistry
chemical_list: D000838:Anions; D002412:Cations; D000644:Quaternary Ammonium Compounds; D013501:Surface-Active Agents; D014867:Water; C013912:decyltrimethylammonium; D008239:Lysine