Self-Assembly of Surfactant Vesicles that Transform into Viscoelastic Wormlike Micelles upon Heating

Abstract

Unilamellar vesicles are observed to form in aqueous solutions of the cationic surfactant, cetyl trimethylammonium bromide (CTAB), when 5-methyl salicylic acid (5mS) is added at slightly larger than equimolar concentrations. When these vesicles are heated above a critical temperature, they transform into long, flexible wormlike micelles. In this process, the solutions switch from low-viscosity, Newtonian fluids to viscoelastic, shear-thinning fluids having much larger zero-shear viscosities (e.g., 1000-fold higher). The onset temperature for this transition increases with the concentration of 5mS at a fixed CTAB content. Small-angle neutron scattering (SANS) measurements show that the phase transition from vesicles to micelles is a continuous one, with the vesicles and micelles coexisting over a narrow range of temperatures. The tunable vesicle-to-micelle transition and the concomitant viscosity increase upon heating may have utility in a range of areas, including microfluidics, controlled release, and tertiary oil recovery.

Influence of Carbon Nanotubes on Surfactants Supramolecular Structures

“…При этом многими авторами отмечено, что для молекул катионного ПАВ цетилтриметиламмоний бромида (ЦТАБ), находящихся в водных растворах, характерно появление наноструктурных образований в виде везикул обычно стандартной сферической формы [14]. В работе [15] нами было показано, что молекулы ЦТАБ могут спонтанно организо-вываться в гораздо более сложные структуры с характерным размером в несколько десятков микрометров.…”

Quantitative Correlation between Counterion (X) Affinity to Cationic Micelles and X-Induced Micellar Growth for X = 2,4-; 2,5-; 2,6- and 3,4-Dichlorobenzoate Ions

“…All the flow curves for MX 2,5-Cl 2 Bz Na of the origin of these maxima is not fully understood at the molecular level 13,31,36 . However, it has become almost certain from these studies 13, 30 35 of CTABr micellar-mediated piperidinolysis of PSa have been described elsewhere 38,40 .…”

“…Kreke et al used 1 H and 13 C NMR studies to show that 2,6-Cl 2 C 6 H 3 CO 2 2,6-Cl 2 Bz and 3,5-Cl 2 Bz counterions were intercalated within the cationic micellar headgroups and that 3,5-Cl 2 Bz counterions inserted further into the interface of rodlike micelles while 2,6-Cl 2 Bz counterions remained at the surface of the spherical micelles 25 . Based upon 1 H, 19 F and 13 C NMR studies, Vermuthen et al concluded that the 2-FC 6 H 4 CO 2 2-FBz counterion penetrates the micellar interface more deeply than 3-FBz and 4-FBz counterions 12 .…”

“…Based upon 1 H, 19 F and 13 C NMR studies, Vermuthen et al concluded that the 2-FC 6 H 4 CO 2 2-FBz counterion penetrates the micellar interface more deeply than 3-FBz and 4-FBz counterions 12 . Micelle formation and growth of aqueous CTAX solutions X 2-ClBz , 4-ClBz , 2,6-Cl 2 Bz , 3,4-Cl 2 Bz and 3,5-Cl 2 Bz have been studied by the use of cryo-TEM images, small angle neutron scattering SANS and rheological measurements 26 .…”

Characterization of dynamics and internal structure of a mixed-surfactant wormlike micellar system using NMR and rheometry

“…Small-angle neutron scattering and dynamic light scattering studies have reported on isotropic to nematic phase transitions, 23 transitions from vesicles to wormlike micelles, 30 the concentration dependence of the hydrodynamic correlation length, 31 and the effect of adding salt on micellar growth. 32 Scattering measurements have also characterized important lengths of the micellar network 33 and have been used to investigate local structure and flexibility.…”