Study of the aggregation of nonylammonium chloride in aqueous solutions ofsodium chloride by vapor pressure osmometry

We determined osmotic coefficients from vapor pressure osmometry (VPO) meas urements on aqueous solutions of nonylammonium chloride in the presence of NaCl at 30 degrees C. VPO data were subsequently used to determine the crit ical micelle concentration (CMC) of the solutions of this surfactant. The v alues of this parameter obtained from VPO are well correlated with those ob tained from light scattering. No premicellar aggregation was observed at su rfactant concentrations below the CMC. The osmotic coefficients below the C MC may be evaluated from the extended form of the Debye-Huckel equation. Ab ove the CMC, the dependence of the osmotic coefficient on the surfactant co ncentration was indicative of the occurrence of aggregation rather than the interactions in the system. Some comments are made on the uncertainty in t he value of some parameters in micellar solutions and possible source of er ror using the VPO technique in these solutions. (C) 1999 Elsevier Science B .V. All rights reserved.