Effect of Temperature and Added Counter Ions on Micelle Formation of Guanidine Surfactants

Abstract Electrical conductivity was measured for aqueous solutions of long-chain guanidine surfactants (G12 and MG12) at different temperatures and with various added counter ions. The critical micelle concentration (cmc) of these surfactants determined from the specific conductivity (κ) vs. concentration (c) plot is lower than those of the typical cationic surfactants, such as alkyltrimethylammonium chloride with the same hydrocarbon chain length. The electrical conductivity data were analyzed according to the mixed electrolyte model of micelle solution, and the degree of counter ion binding (β) was calculated. The thermodynamic parameters for micelle formation were estimated using the values of cmc and β as a function of temperature. The more negative ΔG mic for MG12 indicates more favored micellization. The contribution of entropy term to the micelle formation is superior to that of enthalpy term in the system under study, which indicates micellization is entropy driven. By comparing the cmc and ΔG mic it is evident that all cmc decreases and the more observed negative ΔG mic in the presence of different added salts. The anion effect on the guanidine surfactants micelle formation with added salts showed the micelle forming efficiency order as: Cl − < Br − < NO 3 − < Ac − .