Spontaneous Transition of Micelle–Vesicle–Micelle in a Mixture of Cationic Surfactant and Anionic Surfactant-like Ionic Liquid: A Pure Nonlipid Small Unilamellar Vesicular Template Used for Solvent and Rotational Relaxation Study

Abstract

The micelle-vesicle-micelle transition in aqueous mixtures of the cationic surfactant cetyl trimethyl ammonium bromide (CTAB) and the anionic surfactant-like ionic liquid 1-butyl-3-methylimidazolium octyl sulfate, [C4mim][C8SO4] has been investigated by using dynamic light scattering (DLS), transmission electron microscopy (TEM), surface tension, conductivity, and fluorescence anisotropy at different volume fractions of surfactant. The surface tension value decreases sharply with increasing CTAB concentration up to ∼0.38 volume fraction and again increases up to ∼0.75 volume fraction of CTAB. Depending upon their relative amount, these surfactants either mixed together to form vesicles and/or micelles, or both of these structures were in equilibrium. Fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH), incorporated in this system at different composition of surfactant indicates the formation of micelle and vesicle structures. The apparent hydrodynamic diameter of these large multilamellar vesicles is about ∼200 nm-300 nm obtained by DLS measurement and finally confirmed by TEM micrographs. The large multilamellar vesicles are transformed into small unilamellar ones by sonication using a Lab-line instruments probe sonicator with a diameter of ∼90-125 nm. To investigate the heterogeneity, solvent, and rotational relaxation of coumarin-153 (C-153) have been investigated in these unilamellar vesicles by using picosecond time-resolved fluorescence spectroscopic technique. The solvation dynamics of C-153 in these vesicles is found to be biexponential with average time constant ∼580 ps. This indicates the slow relaxation of water molecules in the surfactant bilayer. In accordance with solvation dynamics, fluorescence anisotropy analysis of C-153 in unilamellar vesicles also indicates hindered rotation compared to bulk water.

Modulation of the aggregation properties of sodium deoxycholate in presence of hydrophilic imidazolium based ionic liquid: water dynamics study to probe the structural alteration of the aggregates

“…The anisotropy decays of C-153 in 20 mM NaDC in the presence of different wt% of [bmim]-BF 4 are shown in Fig. 72 The fast component of the decay remains almost constant with increasing concentration of IL and the slow component increases gradually with increasing concentration of IL and as a result, the average rotational relaxation time also increases. Bhattacharyya et al determined the time resolved anisotropy decays of C-153 by varying the excitation wavelengths and they showed that the anisotropy decays do not show any appreciable dependence on excitation wavelength.…”

5-Methyl Salicylic Acid-Induced Thermo Responsive Reversible Transition in Surface Active Ionic Liquid Assemblies: A Spectroscopic Approach

“…In bulk water, C153 molecule exhibits single exponential decay profile with reorientation time of ∼100 ps. 18 Figure 5b and the corresponding fitted parameters are given in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 13 contribution of 17%). In C 16 …”

“…[9][10][11][12] In aqueous solution, the transition from micelle to vesicle is commonly influenced by various external stimuli; therefore this has been executed by variation in the ratio of cationic and anionic surfactants, polar additives, temperature, salts etc. [13][14][15][16][17][18][19][20][21] The morphology of the aggregates sometimes depends on the nature of additives. 14,[22][23][24][25] Considering the influence of organic additive in aggregate transition, we have been motivated to study micelle-elongated micelle-vesicle transition using room temperature ionic liquids as amphiphiles.…”

Synergism between anionic double tail and zwitterionic single tail surfactants in the formation of mixed micelles and vesicles, and use of the micelle templates for the synthesis of nano-structured gold particles

“…The probe DPH is mostly used in such measurements [60]. Being hydophobic, DPH should prefer the hydrophobic environment of the aggregates.…”