A Thermodynamic Study of Micellization of 3-Alkyloxy-2-hydroxypropyl Trimethylammonium Chloride in Aqueous Solution

The detailed micellization behavior of 3-alkyloxy-2-hydroxypropyl trimethylammonium chloride (R(n)HTACl, 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 (alpha(0)) were estimated from conductivity curves in the temperature range of 293.15 K to 323.15 K. Then the thermodynamic parameters of micellization (Delta G(m)(0), Delta H-m(0), and Delta S-m(0)) 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 (N-agg) of R(n)HTACl was determined through static luminescence quenching, and found that the decreased temperature, the elongation of the alkyl chain length or the increased concentration of R(n)HTACl could lead to an increase of the N-agg.