The detailed micellization behavior of 3-alkyloxy-2-hydroxypropyl trimethylammonium chloride (RnHTACl, n = 12, 14, 16) in aqueous solution was studied by electric conductivity, steady-state fluorescence, and isothermal titration microcalorimetry (ITC) methods. The critical micelle concentration (CMC) and degree of counterion dissociation (α0) were estimated from conductivity curves in the temperature range of 293.15 K to 323.15 K. Then the thermodynamic parameters of micellization (ΔGm0, ΔHm0, and ΔSm0) were calculated by applying a mass-action model equation. On the basis of the ITC results, the CMCs and thermodynamic parameters were also estimated at 293.15 K, which were basically consistent with the results from the conductivity method. According to the Turro–Yekta method, the micelle aggregation number (Nagg) of RnHTACl was determined through static luminescence quenching, and found that the decreased temperature, the elongation of the alkyl chain length or the increased concentration of RnHTACl could lead to an increase of the Nagg.
Simple single-tailed amphiphiles (STAs) can form vesicles in their single-component aqueous solutions, under the mediation of solid surfaces, particularly through a dehydration-rehydration (DHRH) process. However, knowledge about the characteristics of the STA vesicle-systems thus obtained is still lacking. In the current work, the vesicles formed by the simple STAs alkyl trimethylammonium bromides (CnTABs), including dodecyl, tetradecyl, and cetyl ones (DTAB, TTAB, and CTAB), via a DHRH process were chosen. The aggregation numbers of the STA vesicles (Nv) were first estimated, and their fluorescence quenching kinetics was then investigated by the time-resolved fluorescence quenching (TRFQ) technique, which were compared with those of conventional vesicle systems. In particular, the mole fractions of CnTAB existing in the form of micelles (fm) in the vesicle systems were estimated using the TRFQ data. The Nv values of DTAB, TTAB, and CTAB were obtained to be ca. 7.33×104, 8.33×104, and 10.6×104, respectively, similar to those of conventional vesicles. In addition, the values of fluorescence quenching kinetic parameters obtained for the STA vesicle-systems are also similar to those of conventional vesicles. For the STA vesicle systems, vesicles coexist with micelles, but the fm significantly decreases with an increase in chain length. DTAB molecules exist mainly in the form of micelles (with fm ~0.82), while TTAB and CTAB exist mainly in the form of vesicles (with fm ~10‒5). Overall, the properties of STA vesicles are similar to those of conventional vesicles. This work deepens our understanding on the features of simple STA-based vesicles. Key words: Single-tailed amphiphile; Alkyl trimethyl ammonium bromide; Vesicle; Aggregation number; Fluorescence quenching kinetics.
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