Application of Conductance Study to Analyze Micellization Behavior of Cationic Gemini Surfactants in Water and Water-Ethanol Solvent Mixed Media

The paper presents the analysis of micellization behavior of cationic gemini surfactants with similar structures with varying atom number in spacer: heptylene-1,7-bis(dimethyloctylammonium) bromide (8-7-8) and octylene-1,8-bis(dimethyloctylammonium) bromide (8-8-8) in water and water-ethanol solvent mixed media. Experiments were carried out by using conductometric method within the temperature range of 288.15-323.15 K. The values of micellization parameters and thermodynamic functions of aggregation [critical micelle concentration (cmc), the degree of dissociation of micelles (alpha), enthalpy of micellization (Delta H-m degrees), entropy of micellization (Delta S-m degrees), Gibbs free energy of micellization (Delta G(m)degrees] within the temperature range investigated were determined. Based on the investigations performed it has been shown that the systems containing the additives ethanol have a positive value Delta G(trans)degrees, a more positive value Delta G(m)degrees and a higher value of a and, cmc as compared to pure water what confirms that the micellization process is delayed. The less spontaneous micellization behavior was observed for the surfactant with odd number of carbon atoms in spacer: 8-7-8. In this case the value of cmc was higher than the nearest homologues with even number of carbon atoms in spacer (8-8-8 and 8-6-8 surfactants). At higher temperatures, the differences in aggregation behavior became less visible.