| dc.description | Critical micelle concentrations (CMC's), degrees of solubilization, aggregation numbers of the surfactant and alcohol, and degrees of counterion binding have been determined for a number mixed micellar systems consisting of ionic surfactants and medium chain length alkoxyethanols, in order to investigate the role of the ethylene oxide (EO) group in the formation of these mixed micelles. In anionic surfactant/alkoxyethanol mixed micellar systems, NMR paramagnetic relaxation experiments, used to determine the degree of solubilization of the alcohol, indicate a systematic increase in the free energy of transfer of the alcohol from the aqueous to the micellar phase, as the number of EO groups in the alcohol is increased for a given alkyl chain length. At a given concentration of alcohol, CMC's, surfactant aggregation numbers, and degrees of counterion binding are all found to decrease as the number of EO groups in the alcohol is increased, while the alcohol aggregation numbers are observed to increase. This suggests that the EO group imparts a small, but significant contribution to the hydrophobic interactions. However, in cationic surfactant/alkoxyethanol mixed micellar systems, the NMR results indicate that the degree of solubilization is constant for a given series of alkoxyethanols with constant hydrophobic chain length. As well, the CMC values, degrees of counterion binding, and the surfactant and alcohol aggregation numbers are relatively insensitive to the number of EO groups in the alcohol. These results imply that for cationic surfactant/alkoxyethanol mixed micellar systems, the alcohol EO group does not contribute to the hydrophobic interactions. | en_US |
