Mixed micellar aggregates of anionic and nonionic surfactants with short hydrophobic tails. A PGSE-NMR study

Intradiffusion coefficients for the ternary system heavy water-sodium hexan esulfonate (C6SNa)-pentaethylene glycol monohexyl ether (C6E5), in both the premicellar and micellar composition ranges, mere measured by the PGSE-NMR technique at 25 degrees C. Experimental data show the formation of mixed m icelles and allow the determination of the cmc. In the premicellar composit ion range the monomer-monomer interactions are analyzed. The compositions o f the aqueous and micellar pseudophase have been computed in the whole mice llar composition range; they indicate that C6E5 has a larger tendency to fo rm aggregates than C6SNa. The aggregation number and the free energy of mic ellization are calculated and interpreted in terms of interactions among th e tensides in the micellar aggregates. The experimental results have been i nterpreted in terms of a regular solution model, and the interaction parame ter beta is computed. beta increases by increasing the number of micellar a ggregates in the system; this effect can be interpreted in terms of intermi cellar interactions.