Thermodynamic properties and conductivities of some dodecylsurfactants in water

Densities, heat capacities, enthalpies of diln., osmotic coeffs. and conductivities are reported for dodecylamine hydrochloride, dodecyldimethylammonium and dodecyltrimethylammonium chloride in water over a wide range of concn. The last two properties were also measured for dodecyltrimethylammonium bromide. From the thermodn. data, partial molar volumes, heat capacities and relative enthalpies and nonideal free energies and entropies were derived as functions of the surfactant concn. The cmc's and degree of counterion dissocn. were also calcd. from the transport properties. The trends of vols., enthalpies, free energies and entropies are quite regular whereas heat capacities present max. and min. at concns. which depend on the nature of surfactants. Corresponding changes were obsd. in the osmotic coeffs. and specific conductivities. The thermodn. functions of micellization were evaluated on the basis of the pseudo-phase transition model. Finally, the effects of the introduction of Me groups in the hydrophilic moiety of the surfactant and of the nature of the counterion on the thermodn. properties of monomers and micelles are examd.