Micellisation of Cetyltrimethyl Ammonium Bromide in Aqueous-Organic Media

The micellisation behaviour of cetyltrimethylammonium bromide (CTABr) in different mass fraction (17–47) of ethylene glycol (EG), dimethylsulfoxide (DMSO), and dimethylformamide (DMF)–water mixed solvents, was investigated using electrical conductivity measurement at different temperatures (293.1–313.1 k). The critical micelle concentration and degree of counterion dissociation (ii ) values increased with increase in the amount of EG, DMSO, and DMF but micellisation was found to be unfavourable in the presence of the co-solvents. The results of the thermodynamic analysis showed that addition of organic solvents, which are principally located in the bulk phase made the micellisation process less spontaneous. The London dispersion interaction represented the major attraction force for micellisation and micellisation proceeded via an exothermic process. The difference in the magnitude of o m i„S value between the CTAB–water and CTAB–water-co-solvent medium is a pointer to the fact that the micellisation in CTAB–water-co-solvent system is favoured by entropy gain. This indicated that the solvents still controlled the three mdimensional water matrix and the micellisation process of the studied surfactant is exothermic though the positive values of o m i„S , are due to the melting of flickering cluster around hydrocarbon ends of the surfactant monomer and increased the randomness of the hydrocarbon chains in the micelle core.