SOLUBILIZATION OF ALCOHOLS AND ETHOXYLATED ALCOHOLS IN ANIONIC AND CATIONIC MICELLES

Critical micelle concentrations (cmc values) and degrees of solubilization of the alcohol have been determined for a number of mixed micellar systems consisting of ionic surfactants and medium chain length alkoxyethanols. NMR paramagnetic relaxation experiments are used to determine the degree of solubilization of a number of alkoxyethanols in anionic and cationic micelles. In anionic surfactant/alkoxyethanol mixed micellar systems, the results show a systematic decrease in the free energy of transfer of the alcohol from the aqueous to the micellar phase as the number of ethylene oxide (EO) groups in the alcohol is increased for a given alkyl chain length. At a given concentration of alcohol, cmc values decrease as the number of EO groups in the alcohol is increased. This suggests that the EO group imparts a 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 the same hydrophobic chain length, and the cmc values are constant within experimental error. This implies that for cationic micelles, the EO group does not contribute to the hydrophobic interactions in mixed micelle formation.