A study of anionic dye-cationic surfactant interactions in mixtures of cationic and nonionic surfactants

Interactions between anionic azo dye C.I. Acid Red 88 (AR88) and cationic surfactant dodecyltrimethylammonium bromide (DTA) in mixtures of DTA and nonionic surfactant Triton X-100 (TX100) at 25 degreesC have been quantitatively investigated by means of potentiometry based on the DTA surfactant cation-selective electrode. For this reason the treatment of mononuclear complex formation in aqueous solution has been used. Association constants K, for the formation of DTA-AR88 complex in the TX100 solutions of different concentrations in its micellar concentration range have been determined and compared to those obtained in the binary mixtures. It has been observed that the addition of TX100 into the mixture of DTA and AR88 causes a significant decrease of K-1, suggesting that the stability of DTA-AR88 complex is reduced in the presence of TX100 micelles. The results show that the decrease of the value of K, is directly affected by the DTA-TX100 and AR88-TX100 interactions in the solution. Since the solubilization of the DTA-AR88 complexes has been appeared in the TX100 solution our results support the conclusion that adding TX100 influences the hydrophobic-hydrophylic balance of the studied complexes. Comparison of the stability of DTA-AR88 complexes to that obtained between DTA and the anionic azo dye C.I. Acid Orange 7 (AO7) without added TX100 shows that under the same experimental conditions DTA strongly interact with AR88 than with AO7. Such behaviour can be explained as a consequence of more hydrophobic character of AR88 compared to AO7. The addition of TX100 into DTA-AO7 mixtures significantly affects the nature of the binding process. (C) 2002 Elsevier Science Ltd. All rights reserved.