Conductance... Case of micellar systems

5 Conductance in electrolyte mixtures Case of micellar systems 

An interesting application is the description of the conductivity of charged micellar systems, where, for concentrations above the critical micellar concentration (cmc), at least three species are present in the solution. It is well known that surfactants in water form aggregates above the cmc. In the case of ionic surfactants, below the cmc, the solution consists of surfactant monomer ions and their counterions. Above the cmc, there is an effective loss of ionic charges through ion condensation onto the micellar surface, three types of charged species may be then considered in the 

An important problem in the case of micellar solutions is that the various species have very different sizes and electric charges. The MSA may not be valid under such conditions as concentration is increased. Finally, the introduction of an excluded volume in the relaxation terms instead of a real hard-sphere interaction potential 

The first problem is to choose the proper parameters. The data are represented the data as conductance versus the total concentration of monomers as it is done by most authors. The latter quantity is the only one that can be experimental- 

Onsager s conductance is that calculated from Onsager s theory [4]. The diffusion coefficient at infinite dilution D , or its conductance at infinite dilution A , for each ionic species and the electrolyte minimum distance of approaeh awere used. For the counterions, and Br. these two parameters are known. For the monomer surfactant, reasonable radii are chosen. The assumption is that these radii are close to the hydrodynamic radii extracted from the monomeric diffusion coefficient using the approximation of perfect sticking. Then, for an ion J  

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