We have studied the micellization of surfactants SDS, CTAB and tweens-80 using a series of Ethylene glycol/water and formamide/water mixed solvents using surface tension, viscosity and conductance measurements. The results are compared with those reported in pure water for the same surfactants. The critical micelle concentration (cmc) shifts to lower values upon increasing the ratio of Ethylene glycol in the Ethylene glycol /water mixed solvent, while the cmc changes in an opposite way with increasing formamide. Contrary to Ethylene glycol, the formamide/water mixed solvent seems to become a better solvent for the surfactant compared to water and thus disfavors the formation of micelles. We have tried to provide a comprehensive picture of how the presence of cosolvents affects the micelle formation.
