Micellar behaviour of cetyltrimethylammonium bromide in N-methyl acetamide -: alkanol and N,N-dimethyl acetamide -: alkanol mixtures

The critical micelle concentration (c.m.c.) of Cetyltrimethylammonium bromide (CTAB) micellar solution, containing methanol, ethanol, n-propanol, n-butanol and n-pentanol in N-methyl acetamide (NMA) and in N,N-dimethyl acetamide (DMA) has been determined using electrical conductivity and surface tension measurements at various temperatures. Both methods show that micelles are formed in NMA and in DMA solution in absence and 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 NMA and in DMA 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 absence and in presence of n-alkanols to further explain the results. (C) 2002 Elsevier Science B.V. All rights reserved.