Mixed Micelles of Tetradecyltrimethylammonium and n-Alkyltriphenylphosphonium Bromides

Abstract

The critical micelle concentrations (CMC) of binary mixtures of tetradecyltrimethylammonium bromide and n-alkyltriphenylphosphonium bromide (ATPPB) with alkyl chain length of 10, 12, 14, and 16 have been determined in water by conductivity measurements. The CMCs were lower than predicted from ideal mixing theory indicating positive synergistic interactions in mixed micelle formation. The results of the mixed systems were analyzed using the regular solution theory which allowed for the determination of the composition of the mixed micelle, the activity coefficients, and the pair-wise molecular interaction parameter β. The average β values were all negative showing significant deviation from ideality which increases as the chain length of the n-ATPPB increases. The excess free energy of the mixed systems was also calculated, and the values were all negative for the four mixed systems studied, an indication that the mixed micelles are thermodynamically stable relative to the individual component.