Solubilization of 1-Alkanols in Ionic Micelles Measured by Piezoelectric Gas Sensors

The partition coefficients of 1-alkanols (1-butanol to 1-heptanol) between ionic micelles and water, expressed in the mole ratio scale (KN) and in the mole fraction scale (KX), were measured at 25 °C by using polymer-coated piezoelectric gas sensors. While KN is constant over the concentration range measured, KX decreases with increasing mole fraction of the 1-alkanols in micelles. It is demonstrated that KN is equal to the value of KX at infinite dilution. The thermodynamic analysis shows that the micellar palisade supplies the solubilization site for 1-alkanols and is less lipophilic than hydrocarbons and 1-alkanols. The dependence of the partition coefficient on the chain length of the cationic surfactants is explained in terms of the micellar electrostatic potential change on solubilization.