Stability of mixed micelles of cetylpyridinium chloride and linear primary alkylamines

The influence of chain length on the composition of micelles of a binary mixture of cetylpyridinium chloride with 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. 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 (Xim¯). Mixing non-ideality was expressed in terms of the molecular interaction parameter (β12) 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 (ΔGM) and to evaluate the synergistic phenomenon.