Interactions of gemini cationic surfactants with anionic azo dyes and their inhibited effects on dyeability of cotton fabric

The interactions of two anionic azo dyes, Methyl Orange (MO) and Congo Red (CR), with a series of gemini cationic surfactants and dodecyl trimethyl ammonium bromide (DTAB) in aqueous solution have been investigated by means of UV-Vis spectroscopy. It was observed that the aggregation of surfactant and dye takes place at surfactant concentrations far below the critical micelle concentration of the individual surfactants. Aggregations with anionic dyes were reflected by hypsochromic shifts with a decrease in the intensity of absorption band. Further addition of surfactant results in an absorption spectrum of the dye characteristic in the presence of cationic micelles. The results also show bathochromic shifts for MO followed by sharp increase in intensity of the absorption bands at lambda(max) after the CMC points of these surfactants. Such a behavior is observed for CR solutions in higher surfactant concentrations. The inhibiting effect of cationic surfactants on dyeability of cotton fabric with CR has also been studied at three different temperatures (30, 50, 90-92 degrees C). Results show large differences between DTAB and gemini cationic surfactants. (c) 2005 Elsevier Ltd. All rights reserved.