Structural and Dynamical Properties of Ribbonlike Self-Assemblies of a Fluorinated Cationic Surfactant

Abstract

The structural and dynamic properties of low ionic strength micellar solutions of the cationic surfactant perfluorooctylbutane trimethylammonium bromide have been investigated by cryo-TEM, small-angle neutron scattering, small-angle X-ray scattering, T-jump and rheological experiments. The surfactant molecules self-assemble into narrow ribbons with average dimensions on the order of 4 nm x 3 nm, either under salt-free conditions or in the presence of up to 30 mM KBr or NaF. Cryo-TEM also reveals in the salt-free systems the presence of networks of multiconnected micelles. Rheological experiments showed that these surfactant systems exhibit a strong shear-thickening effect even in the presence of up to 30 mM KBr. The T-jump response of the micellar solutions was found to be multiexponential. This observation rules out the presence of only linear micelles with an exponential length distribution and suggests more complex topologies of the micellar aggregates. The relaxation time associated with the predominant process in the T-jump relaxation is strongly correlated to the critical shear rate beyond which shear thickening occurs, thus indicating that this critical shear rate is controlled by the micellar kinetics.

Effect of double quaternary ammonium groups on micelle formation of partially fluorinated surfactant

“…With regard to the monovalent fluorinated surfactant with similar molecules, Buhler et al reported TEM micrographs that show that the partially fluorinated surfactant C 8 F 17 C 4 H 8 N + (CH 3 ) 3 Br -forms narrow ribbon micelles (string-like micelles) in aqueous 24.4 mM solution (ca. cmc  25) [25]. Moreover, the average hydrodynamic radii were 35, 63, 95, and 136 nm for C nÀ1 F 2nÀ1 CH 2 N + (CH 3 ) 3 Cl À (n = 8, 10, 12, and 14, respectively) for the fluorocarbon of alkyl chain at the concentration of 15  cmc at 298.2 K [22].…”

Phase Behavior and Shear Alignment in SWNT‐Surfactant Dispersions

“…TEM at cryogenic temperature (Cryo‐TEM) was used for direct imaging of the solutions and dispersions 23, 39, 40…”

Controlled self-assembly of stomatosomes by use of single-component fluorinated dendritic amphiphiles

“…A similar morphology was recently reported for another fluorinated surfactant. 21 In both cases narrow ribbons are formed instead of the common cylindrical micelles.…”

“…19,20 Besides cylindrical micelles and planar bilayer structures more complex morphologies such as branched cylindrical micelles, rings, perforated bilayer vesicles, and mesh phases have been reported. [21][22][23][24][25][26][27] In particular, the morphologies with non-constant interfacial curvatures (bicontinuous phases) are interesting at a fundamental level in order to understand why they form. 28,29 Fluorinated amphiphiles are also interesting for applications.…”