Vesicle–micelle transition in aqueous mixtures of the cationic dioctadecyldimethylammonium and octadecyltrimethylammonium bromide surfactants

Abstract

The vesicle-micelle transition in aqueous mixtures of dioctadecyldimethylammonium and octadecyltrimethylammonium bromide (DODAB and C(18)TAB) cationic surfactants, having respectively double and single chain, was investigated by differential scanning calorimetry (DSC), steady-state fluorescence, dynamic light scattering (DLS) and surface tension. The experiments performed at constant total surfactant concentration, up to 1.0 mM, reveal that these homologous surfactants mix together to form mixed vesicles and/or micelles, depending on the relative amount of the surfactants. The melting temperature T(m) of the mixed DODAB-C(18)TAB vesicles is larger than that for the neat DODAB in water owing to the incorporation of C(18)TAB in the vesicle bilayer. The surface tension decreases sigmoidally with C(18)TAB concentration and the inflection point lies around x(DODAB) approximately 0.4, indicating the onset of micelle formation owing to saturation of DODAB vesicles by C(18)TAB molecules. When x(DODAB)>0.5 C(18)TAB molecules are mainly solubilised by the vesicles, but when x(DODAB)<0.25 micelles are dominant. Fluorescence data of the Nile Red probe incorporated in the system at different surfactant molar fractions indicate the formation of micelle and vesicle structures. These structures have apparent hydrodynamic radius R(H) of about 180 and 500-800 nm, respectively, as obtained by DLS measurements.

Effect of Sonication on the Thermotropic Behavior of DODAB Vesicles Studied by Fluorescence Probe Solubilization

“…The T m data for sonicated DODAB vesicles here reported are in good agreement with previously reported values obtained by other techniques [4,[29][30][31][32]. Small deviations in the experimentally obtained T m may be attributed the different vesicle preparation protocols, lipid source, solvent conditions or method to obtain T m .…”

Reversible Switching of a Micelle‐to‐Vesicle Transition by Compressed CO2

“…The phenomenon was consistent with previous reports of the MVT. [37] When the pressure was over 5.50 MPa, the emission intensity was unchanged with increasing pressure, thus implying that the MVT had finished. The same trend was also observed in the variation of the maximum emission wavelength l max of NR ( Figure 5).…”

“…This method is often used to monitor the course of the MVT in the cationic/anionic surfactant systems. [37,40] In the micelle solution, pyrene may easily enter the inner nonpolar center of the micelles and show the local environment. In vesicles, pyrene is solubilized in the bilayer.…”

Aqueous dispersions of nanostructures formed through the self-assembly of iminolipids with exchangeable hydrophobic termini

“…Spectroscopic changes in NR emission can also suggest if either micelles (emission ≥ 640 ± 2 nm) or vesicles (emission ≤ 636 nm) are formed. 4,21 However addition of this fluorescent probe (1 μM) to the sonicated suspension of 1 in water gave emission between these values, at 638 ± 2 nm ( Figure 3a). In contrast, addition of NR to a sonicated Please do not adjust margins Please do not adjust margins suspension of DDAB (4.6 mM) gave emission at 628 ± 2 nm, consistent with the reported formation of vesicles.…”

“…In contrast, addition of NR to a sonicated Please do not adjust margins Please do not adjust margins suspension of DDAB (4.6 mM) gave emission at 628 ± 2 nm, consistent with the reported formation of vesicles. 4c, 21 Analysis of a suspension of 1 in water by dynamic light scattering (DLS) was similarly inconclusive due to poor data quality, whereas DLS data from DDAB suspensions was consistent with vesicles of ca. 40 nm diameter.…”