The effect of organic additives on critical micelle concentration of non-aqueous micellar solutions

The critical micelle concentration (c.m.c.) of various surfactants, such as sodium caprylate, sodium laurate, sodium palmitate and sodium stearate micellar solution, containing methanol, ethanol, n-propanol, n-butanol and n-pentanol in formamide has been determined using electrical conductivity and surface tension measurements at various temperatures. Both methods show that micelles are formed in formamide solution in presence of n-alkanols. Critical micelle concentrations have also been measured as a function of the concentration of alcohol added. It is suggested that alcohol addition leads to an increase in formamide penetration into the micellar interface that depends on the alcohol chain length. The results are discussed in terms of: (1) alcohol penetration of the micelles; and (2) solvent structuring. Thermodynamic parameters were evaluated for micellar systems in presence of n-alkanols to further explain the results.