Coductometric studies of the interaction of acid green 25 with cationic alkyltrimethylammonium bromid surfactants

The interactions between an anionic dye, Acid Green 25 AG and the two cationic surfactants tetradecyltrimethylammonium bromide TTAB, and hexadecyltrimethylammonium bromide CTAB in aqueous solutions far below the CMC are studied using the conductometric method at different temperature. The equilibrium constants and other thermodynamic functions for the process of dye-surfactant ion pair formation were calculated by the conductometric data. The results showed that the surfactant which contained the longer hydrophobic chain had a stronger tendency to associate with the dye and the equilibrium constant was considerably higher than those measured for the surfactant with the shorter hydrophobic chain. These results indicate that short range, non-electrostatic interactions have a significant influence on dye -surfactant ion pair formation as well as long range electrostatic forces.