The Interaction between an Anthraquinoid Acidic Dye and Cationic Surfactant

The interaction between an anthraquinoid acidic dye and hexadecyltrimethylammonium bromide (HTAB) was studied spectrophotometrically. Three types of interactions were turned out; (1) The dye formed insoluble 1 : 1 salt with HTAB in the presence of excess dye. In this case, most of the added HTAB was consumed for the salt-formation. (2) The resolution of dye-surfactant salt was brought about in the presence of excess HTAB over the dye concentration. This was explained as the result of complex formation. The complex was estimated to consist of a single dye and three HTAB molecules. The complexed dye was surrounded with the rather hydrophilic environment in this case. (3) In the region of micelle formation of the surfactant, some of dye complexes penetrated into micelles. The cmc of this system was calculated to be 0.49mM from the absorbance measurement. Above cmc, the dyes were distributed to both the complex and the micelle ; the distribution coefficient (K) was 1.02×102. The standard free energy change of dye penetration (G0p) was determined to be -0.30kcal·mol-1. The number of penetrated dye molecules into a single micelle was calculated.