title: Effect of counterions on the shape, hydration, and degree of order at the interface of cationic micelles: the triflate case.
abstract: Specific ion effects in surfactant solutions affect the properties of micelles. Dodecyltrimethylammonium chloride (DTAC), bromide (DTAB), and methanesulfonate (DTAMs) micelles are typically spherical, but some organic anions can induce shape or phase transitions in DTA(+) micelles. Above a defined concentration, sodium triflate (NaTf) induces a phase separation in dodecyltrimethylammonium triflate (DTATf) micelles, a phenomenon rarely observed in cationic micelles. This unexpected behavior of the DTATf/NaTf system suggests that DTATf aggregates have unusual properties. The structural properties of DTATf micelles were analyzed by time-resolved fluorescence quenching, small-angle X-ray scattering, nuclear magnetic resonance, and electron paramagnetic resonance and compared with those of DTAC, DTAB, and DTAMs micelles. Compared to the other micelle types, the DTATf micelles had a higher average number of monomers per aggregate, an uncommon disk-like shape, smaller interfacial hydration, and restricted monomer chain mobility. Molecular dynamic simulations supported these observations. Even small water-soluble salts can profoundly affect micellar properties; our data demonstrate that the -CF3 group in Tf(-) was directly responsible for the observed shape changes by decreasing interfacial hydration and increasing the degree of order of the surfactant chains in the DTATf micelles.
authors.affiliation: Instituto de Química, Universidade de São Paulo, São Paulo, Brazil.
authors.forename: Filipe S
authors.initials: FS
authors.lastname: Lima
authors.forename: Iolanda M
authors.initials: IM
authors.lastname: Cuccovia
authors.forename: Dominik
authors.initials: D
authors.lastname: Horinek
authors.forename: Lia Q
authors.initials: LQ
authors.lastname: Amaral
authors.forename: Karin A
authors.initials: KA
authors.lastname: Riske
authors.forename: Shirley
authors.initials: S
authors.lastname: Schreier
authors.forename: Roberto K
authors.initials: RK
authors.lastname: Salinas
authors.forename: Erick L
authors.initials: EL
authors.lastname: Bastos
authors.forename: Paulo A R
authors.initials: PA
authors.lastname: Pires
authors.forename: José Carlos
authors.initials: JC
authors.lastname: Bozelli
authors.forename: Denize C
authors.initials: DC
authors.lastname: Favaro
authors.forename: Ana Clara B
authors.initials: AC
authors.lastname: Rodrigues
authors.forename: Luís Gustavo
authors.initials: LG
authors.lastname: Dias
authors.forename: Omar A
authors.initials: OA
authors.lastname: El Seoud
authors.forename: Hernan
authors.initials: H
authors.lastname: Chaimovich
mesh_terms: D002412:Cations / Q000737:chemistry; D008698:Mesylates / Q000737:chemistry*; D008823:Micelles; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D013501:Surface-Active Agents / Q000737:chemistry
chemical_list: D002412:Cations; D008698:Mesylates; D008823:Micelles; D000644:Quaternary Ammonium Compounds; D013501:Surface-Active Agents; C583589:dodecyltrimethylammonium triflate; C022806:dodecyltrimethylammonium; C012077:trifluoromethanesulfonic acid