Micellization pattern of cationic surfactants in presence of azo dye in methanol mixed media

Conductivity measurements at three different temperatures (298.15, 308.15, and 318.15 K) were performed to determine the micellization nature of cationic surfactants, i.e., dodecyl trimethylammonium bromide (DTAB) and cetylpyridinium chloride (CPC), in the absence and presence of the azo dye methyl red (MR) in four mixed solvent systems (0.1 to 0.4) volume fraction of methanol in water. We calculated the critical micelle concentration (CMC) of DTAB and CPC and the degree of ionization (alpha) for both in the absence and presence of MR using William's method. The interaction of surfactants DTAB and CPC with MR has been identified separately through the dye-surfactant aggregation process, with reduced CMC values due to the molecular reorientation of methyl red in the systems. Micellization becomes more likely with MR due to the formation of a molecular complex in mixed systems. We calculated different thermodynamic properties both in the absence and presence of methyl red. Such parameters are the standard Gibbs free energy of micellization (Delta Gom), the standard enthalpy of micellization (Delta Hom), the standard entropy of micellization (Delta Som), the standard free energy of transfer (Delta Gotrans) and heat capacity of micellization (Delta mC0p). In accordance with Delta Gom values, the mixtures show the spontaneous nature of micellization of DTAB and CPC with MR as well.