Study of Fuchsin Acid Fading in Micellar Media

The rate constant of alkaline fading of fuchsin acid (FA^2?) was measured in the presence of nonionic (TX‐100), cationic (dodecltrimethylammonium bromide, DTAB), and anionic (sodium dodecyl sulfate, SDS) surfactants. FA^2? has three negatively charged substituents and one positive charge, and this makes the behavior of FA^2– different from dyes such as bromophenol blue. It was observed that the reaction rate constant decreased in the presence of TX‐100, DTAB, and SDS. Binding constants of FA^2? to TX‐100, DTAB, and SDS and the related thermodynamic parameters were calculated by the stoichiometric (classical) model. The results show that the binding of FA^2? to SDS is endothermic in both regions, and the binding of FA^2? to DTAB and TX‐100 is exothermic in one region and endothermic in another region of the used concentration range of these surfactants. Also, the binding constants of FA^2? to surfactant molecules of SDS/TX‐100 and DTAB/TX‐100 mixed micelles were obtained.