SOLUTION BEHAVIOR OF DYE-SURFACTANT ASSOCIATIONS

Association of water soluble anionic dyes and different types of surfa ctants has been studied in aqueous solutions. The anionic dyes were Re mazol Red F3B and Remazol Brilliant Yellow GNL. Surfactants belonging to different classes were studied: anionic (SDS), cationic (DTAB), non ionic (OPE09), and zwitterionic (DDAPS). The two dyes were shown to ag gregate in water when their concentration is above a threshold value. Evidence for the formation of mixed micelles could be obtained by mean s of H-1 NMR experiments. The surface tension lowering and critical mi cellar concentration (cmc) values of dye-surfactant mixtures were inte rpreted on the same grounds as those for surfactants mixtures. The reg ular solution theory originally proposed by Lange and Beck was used, t he threshold concentration value for dye aggregation being considered as a cmc value. Deviations from ideal behavior were observed and evalu ated, depending on the type of surfactant. Precipitation was observed with mixtures of anionic dyes and cationic surfactants, indicating str ong interactions between them. Experiments indicated a strong synergis m with a zwitterionic surfactant, and a moderate deviation from ideal behavior with anionic and nonionic ones. NMR experiments have shown th at dyes are located at the interface in the mixed micelles. Some corre lations between solubilization site and synergism in mixed micelle for mation could be disclosed. (C) 1994 Academic Press, Inc.