Heat Capacity of Micellization of Lithium Perfluoroalkanoates in Aqueous Solution

Specific heats of aqueous solutions of lithium perfluoroalkanoates, from C-6 to C-9, were determined at 298.15 K at concentrations below and above the critical micelle concentration. Infinite dilution apparent molar heat capacities are compared with literature data for corresponding salts with different counterions. Heat capacities of micellization of these surfactants in water were calculated from the specific heat data and also by measurements of the heat of micellization at two temperatures, 298.15 K and 308.15 K. The data were treated under the assumption of the pseudo-phase separation model. The two series of data agree in the case of perfluorononanoate but diverge for perfluorosurfactants with shorter hydrophobic chains. The results are interpreted in terms of the extent of the applicability of the adopted chemical model. Heat capacities of the micellization process obtained from experimental specific heats compare well with literature values relative to the sodium salts of the examined anions.