ABSTRACT
The influence of chain length and the nature of the head group on the composition of micelles of a binary mixture of cetyltrimethylammonium chloride with both unsubstituted and N-substituted n-octyl, n-decyl, and n-lauryl amines was established from the variation of the critical micelle concentration (cmc) as a function of the solution composition. A synergistic effect was observed in all instances that were found to be correlated with chain length and the type of N-substituent on the alkylamine head group. Experimental data were compared with theoretical predictions based on the equilibrium between micelles and monomers in solution. The Motomura treatment was used to determine the composition of each compound in the mixed micelles (Xi(m)). Mixing nonideality was expressed in terms of the molecular interaction parameter (beta12) as determined using the theory of Holland and Rubingh. Finally, the molecular thermodynamic model for mixed surfactant systems developed by Puvvada and Blankschtein was used to estimate the micellization free energy (DeltaGM) and to evaluate the synergistic phenomenon.
ABSTRACT
The application of a statistical method, the local polynomial regression method, (LPRM), based on a nonparametric estimation of the regression function to determine the critical micelle concentration (cmc) is presented. The method is extremely flexible because it does not impose any parametric model on the subjacent structure of the data but rather allows the data to speak for themselves. Good concordance of cmc values with those obtained by other methods was found for systems in which the variation of a measured physical property with concentration showed an abrupt change. When this variation was slow, discrepancies between the values obtained by LPRM and others methods were found.
