A comparison of micelle formation of ionic surfactants in formamide, in N-methylformamide and in N,N-dimethylformamide

Critical micelle concentrations (c.m.c.) were determined from electrical conductivity and surface tension measurements of various ionic surfactants, such as sodium caprylate, sodium laurate, sodium palmitate and sodium stearate, in formamide (FA), in N-methylformamide (NMF) and in N,N-dimethylformamide (DMF) at 25 °C. Both methods show that micelles are formed in FA, in NMF and in DMF solutions. The c.m.c. were considerably lower in FA, and in NMF, and higher in DMF, than in water. It is suggested that amphiphilic self-assembly is a physical process that occurs in FA, in NMF and in DMF and the driving force for micelle formation correlates with solvophobicity. The surfactant–solvent interactions that drive amphiphilic self-organization in FA, in NMF and in DMF are discussed. These results are also explained by the structure of FA, NMF and of DMF. Thermodynamic parameters were evaluated for micellar systems to explain the results.