Aggregation properties and thermodynamics of micellization of gemini surfactants with diamide groups and rigid spacers in water and water-organic solvent mixed media

Abstract

The aggregation behavior and thermodynamics of micellization of three gemini surfactants with diamide groups and rigid spacers in various volume percentages of ethylene glycol (EG-WR) and three different types of 10% organic co-solvents (MA-WR, DMF-WR and AN-WR) across a range of temperature from (281.15 to 331.15) K, have been investigated by electrical conductivity measurements. The properties parameters including critical micelle concentration (CMC), degree of counter ion dissociation (α) were determined and discussed. The thermodynamic parameters of micellization including standard Gibbs energy (ΔG°m), Gibbs energy of transfer (ΔG°trans), Gibbs energy of micellization per alkyl tail (ΔG°tail), standard enthalpy (ΔH°m) and standard entropy (ΔS°m) were calculated from the temperature dependence of the CMC and α values. With the increasing chain length, the CMC of gemini surfactants decreased. At a given temperature, The CMC and α values are found to increase with the increasing percentage of EG content in the mixed solvent. The temperature dependence of ΔG°m and CMC values for the gemini surfactants in all the investigated systems is U-shaped. Compensation of enthalpy and entropy of micellization of all three gemini surfactants were observed in all the studied mixed media.