Spectrophotometric study of anionic azo-dye light yellow (X6G) interaction with surfactants and its micellar solubilization in cationic surfactant micelles

Solubilization and interaction of azo-dye light yellow (X6G) at/with cationic surfactants cetyltrimethylammonium bromide (CTAB) and cetylpyridinium chloride (CPC) was investigated spectrophotometricaly. The effect of cationic micelles on solubilization of anionic azo dye in aqueous micellar solutions of cationic surfactants was studied at pH 7 and 25 °C. The binding of dye to micelles implied a bathochromic shift in dye absorption spectra that indicates dye–surfactant interaction. The results showed that the solubility of dye increased with increasing surfactant concentration, as a consequence of the association between the dye and the micelles. The binding constants, Kb, were obtained from experimental absorption spectra. By using pseudo-phase model, the partition coefficients between the bulk water and surfactant micelles, Kx, were calculated. Gibbs energies of binding and distribution of dye between the bulk water and surfactant micelles were estimated. The results show favorable solubilization of dye in CTAB micelles.