Investigation of Micellization Properties of some Ionic Surfactants in Water + Formamide Solutions at Various Temperatures

The critical micelle concentration (CMC) of sodium dodecyl sulphate (SDS) and cetyltrimethylammonium bromide (CTAB) in water, 25, 50 and 75% (v/v) formamide (FA) + water and pure FA has been determined at various temperatures by means of specific conductivity measurements. The standard free energy (ΔG⁰_m), enthalpy (ΔH⁰_m) and entropy of micellization (ΔS⁰_m) were calculated from these data. The experimental results indicate that the CMC of both the ionic surfactants, SDS and CTAB, initially increases then decreases as the concentration of the organic solvent, FA in water is increased. The trends in the values of ΔG⁰_m, ΔH⁰_m and ΔS⁰_m indicate that the micellization of SDS and CTAB in FA + water mixture is an entropy-directed process. Furthermore, the effect of temperature on micellization has also been discussed.