Octanol-Triggered Self-Assemblies of the CTAB/KBr System: A Microstructural Study

Abstract

A micelle-vesicle transition induced by n-octanol C(8)OH was observed in an aqueous cetyltrimethylammonium bromide (CTAB)/potassium bromide (KBr) system. This transition was investigated by viscosity, rheology, dynamic light scattering (DLS), and direct imaging technique, cryo-transmission electron microscopy (cryo-TEM). Viscometry shows that the system underwent several morphological transitions with the increase in concentration of C(8)OH (regions I-IV). At low octanol concentration (region I), DLS analysis showed an increase in the apparent hydrodynamic diameter of the micelles with the addition of C(8)OH which was supported by cryo-TEM and rheology. With further addition of C(8)OH, transition of the elongated micelles occurred to a viscoelastic fluid comprising entangled wormlike micelles (region II), for which rheological data can be described by the Maxwell model. Further, the wormlike micelles transform to vesicles at [C(8)OH] ≈ 0.020 M (region III). This transition and the consequent changes in the fluid response can be explained in terms of vesicle formation caused by further addition of C(8)OH. Beyond this concentration (region IV), vesicles are the predominant microstructures in the system which shows unusual temperature response.

Thermo-responsive Wormlike Micelles

“…Sreejith et al [53] investigated the mixture of CTAB and C 8 OH in the presence of KBr (Fig. 2.4d) and observed a thermally-induced response for C 8 OH/CTAB molar ratios above ~0.25.…”

Micellar growth of m-2-m type gemini surfactants (m=10, 12, 14) with higher chain length alcohols/amines (C6–C8) in the absence and presence of organic salts (sodium salicylate, sodium tosylate)

“…The lower homologues affect the water structure, while the penetration of higher ones outweighs the effect, resulting in an increase of both the micellar size and viscosity, hence promoting micellar transition. Thus, alcohols/amines with long chains are employed in industrial applications as they are potential candidates to induce a rich variety of microstructures [6,7].…”

1-Hexanol triggered structural characterization of the worm-like micelle to vesicle transitions in cetyltrimethylammonium tosylate solutions

“…With increase in [CTAT], the maximum shis to lower 1-hexanol concentration. 49 In 30 mM CTAT, the viscosity directly decreases without showing any maximum. This may be due to a more compact packing of micelles at higher [CTAT] which does not allow 1-hexanol molecules to penetrate.…”

“…A detailed study on formation of vesicles from CTAB micelles in the presence of KBr has been reported for 1-octanol and it was concluded that sudden drop in viscosity aer maximum is due to formation of vesicles. 49 It is well reported that 1-octanol increases the aggregation number by forming mixed micelles. 45,49 It is obvious from above observations that 1-hexanol and 1-octanol are capable of forming vesicles from single surfactant solution while ethanol and 1-butanol are not.…”

“…49 It is well reported that 1-octanol increases the aggregation number by forming mixed micelles. 45,49 It is obvious from above observations that 1-hexanol and 1-octanol are capable of forming vesicles from single surfactant solution while ethanol and 1-butanol are not. In the present study, due to more hydrophobic nature of 1-octanol, it intercalates between CTAT charged head groups and leads to a large increase in viscosity than 1-hexanol at much lower concentration.…”