COMPLETE THERMODYNAMIC PROPERTIES OF NONYLTRIMETHYLAMMONIUM AND DECYLTRIMETHYLAMMONIUM BROMIDES IN WATER

The freezing point depressions, enthalpies of dilution, sound velocities, volumetric heat capacities, and densities were measured for nonyltrimethylammonium bromide (NTABr) and decyltrimethylammonium bromide (DTABr) in water over a large concentration region. The last two properties were measured as a function of temperature. From these data the nonideal free energies and entropies and the partial molal relative enthalpies, heat capacities, volumes, and expansibilities and compressibilities were derived. With the exception of compressibilities all other functions were determined as a function of temperature. The thermodynamic functions of micellization, defined as the molar change in property at the CMC, were calculated as a function of temperature. It is important in this respect to use excess entropies S ̄2 - S ̄20 and not only the nonideal contribution S ̄2ni. All these data are self-consistent as a function of temperature, and the experimental free energies of micellization obtained from enthalpies and entropies are equal to zero, inside the experimental uncertainty, as expected from the equilibrium situation. The properties of the monomers and of the micelles and the trends in micellization functions are all consistent with current ideas on hydrophobic solutes and micelles. © 1979.