SOLUBILIZATION TENDENCY OF 1-ALKANOLS AND HYDROPHOBIC INTERACTION IN SODIUM LAURYL SULFATE IN ORDINARY WATER, HEAVY-WATER, AND UREA SOLUTIONS

The effects of 1-propanol, 1-butanol, 1-hexanol, and 1-octanol on the micellization parameters of sodium lauryl sulfate (NaLS) in heavy water (D2O) and in aqueous urea solutions, solvent systems with stronger and weaker hydrogen-bonded skeletal structures, respectively, than in ordinary water, have been determined at 25°C. We have also determined the transfer free energy of an alcohol from H2O to D2O and also to urea solutions by head space gas chromatography. Results show the following: (1) The ability to depress the critical micelle concentration (cmc) increases in going from D2O to H2O to 5 M urea, the direction of decreasing structuredness of the solvent system. (2) The coaggregation equation (J. Phys. Chem. 1983, 87, 5443), relating the ability to depress the cmc and the ability to increase the micellar degree of ionization to the distribution coefficient of the amphiphilic additive between the micelles and the surrounding solvent phase, is applicable in all these solvent systtems. (3) The transfer free energy from micelles in H2O to micelles in urea solutions is positive and increases with urea concentrations for propanol and essentially butanol, while it is negative for hexanol and octanol and decreases with increasing urea concentration tending to reach a minimum at about 4 and 3 M urea, respectively. (4) The transfer free energy from micelles in H2O to micelles in 3 M urea solutions tends to decrease with increasing alcohol chain length while it tends to increase for the transfer to micelles in D2O. The results are interpreted in terms of the effect of the solvent "structuredness" on the extent of the hydrocarbon-solvent contact region in the micelles and the ability of an alcohol to reduce the extent of that region. © 1990 American Chemical Society.