Structural Evolution in Cationic Micelles upon Incorporation of a Polar Organic Dopant

Abstract

Micelles of cetyltrimethylammonium bromide (CTAB), when doped with increasing levels of 4-ethylphenol, show microstructural transitions from spherical micelles to elongated wormlike micelles, disks, and subsequently to globular and then to tubular vesicles. Wormlike micelles are observed at a dopant-to-CTAB molar ratio of 1:3. At higher dopant ratios (1:1), globular vesicles are observed which transition to tubular vesicles when the dopant becomes the predominant species at a ratio of 3:1. These transitions are reflected in small-angle neutron scattering analysis and, interestingly, can be directly observed through cryo-transmission electron microscopy. The para-substituted phenol is interfacially active and modulates interfacial curvature of the micelles. The observations of microstructure modifications have relevance to the synthesis of mesoporous materials using CTAB as the template.

Hydrogen‐Bonded Large Molecular Aggregates of Charged Amphiphiles and Unusual Rheology: Photochemistry and Photophysics of Hydroxyaromatic Dopants

“…Changes in microstructure of surfactant aggregates that are induced by the addition of a series of phenolic organic dopants (phenol, cresol and alkyl-substituted phenols, namely 4-ethyl phenol, 4-n and i-butyl phenol) to a micellar solution of CTAB have been studied using cryogenic transmission electron microscopy (cryo-TEM) [61][62][63]. As the concentration of each of the dopants is increased, there is a systematic reduction in the curvature of the observed microstructure.…”

Thermal Behavior of Dodecylpyridinium-Based Surfactant Salts with Varied Anionic Constituent

“…The design of new materials, especially nanomaterials based on self-organization procedure has been one of the main focus in the field of supramolecular chemistry. 2 There is a multitude of interesting structures including micelles with different sizes and shapes, 3 bilayer vesicles 4,5 and liquid-crystalline mesophases 6 that are formed during interactions of amphiphiles. Previous studies have also reported formation of ribbons, 7,8 disks, 9 and gel-like crystalline mesophases that are used to template materials in both aqueous and/or nonaqueous domains.…”

Impact of Phenolic Antioxidants on Structural Properties of Micellar Solutions

“…Various studies using a variety of techniques such as rheological approaches, [7][8][9][10][11][12] birefringence, 8 NMR, 4,5,8,13,14 heat capacity, 15 acidity, 13 neutron reflectivity, 6 surface tension, 16 and SANS measurements 4,17,18 have been performed on the influence of organic counterions on cationic surfactants. It has been demonstrated that aromatic counterions are more effective at lower concentrations than salts or electrolytes in inducing the micellar growth, 6,13,19 which can be attributed to interactions with the aromatic π-electron system.…”

“…13 Particularly aromatic anions like hydroxyand chlorobenzoates and phenols have been investigated for inducing the elongation of CTAB micelles. [4][5][6]9,11,12,18,20,21 Substituents and their position on the aromatic ring system play an important role in micellar growth. While hydroxyl groups in the ortho-position induce growth, those in the para-and meta-position do not.…”

“…A symmetrical shape is related to spheres while an unsymmetrical shape indicates cylindrical micelles, with the axial length of the cylinder being responsible for the linear region of p(r) for a large r. 18 The scattering curve I(q) showed a q −1 dependence. This strongly supports the rodlike shape of aggregates.…”