Thermodynamic study of interaction between a cationic surfactant and an anionic azo dye in aqueous solution

The interactions between an anionic azo dye Acid Orange 5 (AO5) and the cationic surfactant cetyltrimethylammonium bromide (CTAB) have been studied by conductometric and surfaCe tension. The effect of increasing the proportion of dye on the Critical Micelle Concentrations (CMC) of surfactant, as well as the impact of increased temperature, has been investigated to understand the different types of interactions for the formation of a dye-surfactant ion pair. The results revealed that the CMC values have reflected a tendency towards increasing in the values with increasing in the proportion of the azo dye in the surfactnt solutions which is unfavorable for micellization. It has been concluded that the relation between temperatures and CMC followed U-shape behavior in dye-surfactant mixture solutions. Significantly, the interactions of dye-sUrfactant are spontaneous based on the negative values of Delta G(mic)(0) for all systems. However, at low temperatures; the micellization process is endothermic (Delta H-mic(0) > 0) of dye-surfactant mixture solutions, and become exothermic (Delta H-mic(0) < 0) at high temperatures. The entropy contribution of micelle formation, Delta S-mic(0) presents positive values.