Thermochemical study of aqueous micellar solutions of some amphiphilic quaternary ammonium chlorides at 313 K

The heats of diln. and osmotic coeffs. of N-dodecyl-N-benzylmorpholinium chloride (DBeMC), N-dodecyl-N-methylmorpholinium chloride (DMeMC) and dodecyltrimethylammonium chloride (DTAC) were measured by using a LKB flow microcalorimeter and a vapor pressure osmometer at 40°. The relative apparent and partial molar enthalpies, free energies, and entropies were derived as a function of surfactant concn. The pseudo-phase sepn. model was used to obtain graphically the crit. micelle concn. (c.m.c.) and enthalpy of micellization. Micellization heat capacities were also evaluated. The studies confirm that the benzyl group of DBeMC behaves as a second chain with respect to the micellization process. It was also possible to est. its length as similar to that of an alkyl chain of 5 carbon atoms. The packing parameter of DBeMC indicates the formation of non-spherical aggregates by this surfactant.