THERMOCHEMICAL STUDY OF AQUEOUS MICELLAR SOLUTIONS OF SOME AMPHIPHILIC QUATERNARY AMMONIUM CHLORIDES AT 313-K

The heats of dilution and osmotic coefficients of N-dodecyl-N-benzylmorpholinium chloride (DBeMC), N-dodecyl-N-methylmorpholinium chloride (DMeMC) and dodecyl-trimethylammonium chloride (DTAC) were measured by means of an LKB flow microcalorimeter and a vapor pressure osmometer at 40-degrees-C. The relative apparent and partial molar enthalpies, free energies and entropics were derived as a function of surfactant concentration. On the basis of the pseudo-phase separation model, the values of critical micelle concentration (c.m.c.) and enthalpy of micellization were graphically evaluated. Micellization heat capacities were also evaluated. The studies confirmed that the benzyl group of DBeMC behaves as a second chain with respect to the micellization process. It was also possible to estimate its "length" as similar to that of an alkyl chain of five carbon atoms. From these results, the packing parameter of DBeMC was evaluated and the formation of non-spherical aggregates by this surfactant was suggested.