Exploring the interactions of anionic dye tartrazine with cationic surfactants in aqueous solution: Insights into micellization and interfacial properties

Abstract

Different techniques such as conductometric, tensiometric and spectroscopic methods were deployed to investigate the interactions of tartrazine (TZ) dye with cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPB) in aqueous media at four temperatures. Results revealed a lower cmc values for CPB as compared to CTAB in presence/or absence of aqueous TZ solutions. A qualitative analysis, using UV–vis spectroscopy, was carried out to understand the interactions between the dye TZ and CTAB/CPB in the premicellar and post micellar phase. Interfacial properties such as surface excess concentration (Γmax), area occupied per surfactant molecule (Amin), surface pressure (πcmc), standard Gibbs energy of adsorption (ΔGado), packing parameter (P), etc., were evaluated at air–water/aqueous TZ solution of CTAB/CPB. The equilibrium model was used to determine the change in standard Gibbs energy (ΔGm0), enthalpy (ΔHm0), and entropy (ΔSm0) of micellization. Due to the interruption of the structured water molecules encasing the hydrophobic groups of the surfactant, the critical micelle concentration (cmc) rose with temperature. For both the studied systems, the values of ΔGm0 and ΔHm0 were negative, implying that the process of micellization is thermodynamically spontaneous and exothermic. The -TΔSm0 values, which were found to be greater than ΔHm0 values, suggest the gain in entropy primarily governs the process of micellization.