Dimerization of the methylviologen cation radical in anionic micellar and polyelectrolyte solutions

The dimerization behavior of the methylviologen cation radical (MV**. ** plus ) in the presence of sodium dodecyl sulfate (SDS), sodium decyl sulfate (SdecS), and sodium poly(styrenesulfonate) (PSS) was examined by using the visible spectal characteristics of solutions containing electrogenerated MV**. ** plus +ZZThe results indicate that the concentration of either SDS or SdecS micellar aggregates exerts a strong effect on the extent of dimerization. Thus, negligible dimerization was found at high levels of surfactant while extensive dimerization was observed at surfactant concentrations slightly above the corresponding critical micelle concentrations. This behavior was reasonably well simulated by a simple computational model based on the Poisson distribution. The dimerization pattern in the presence of PSS was quite different. The polyelectrolyte was found to increase the dimerization level, throughout the entire concentration range surveyed (5-100 mM), over that found in isotropic aqueous solutions. This was interpreted as the result of MV**. ** plus clustering triggered by the polyelectrolyte chains.