The Partitioning off Neutral Solutes Between Micelles and Water as Deduced from Critical Micelle Concentration Determinations
384The partition coefficient P of neutral solutes between micelles and water can be deduced from the analysis of the decrease of the initial rate of change of the critical micelle concentration (CMC) of a surfactant with the addition of the solute, provided an adequate model of surfactant/solute interaction in dilute solutions can be defined. The various models available in the literature are critically reviewed, and the results deduced from various experimental approaches are compared. P values are calculated for over 200 surfactant/solute systems using a suggested best procedure based upon experimental data. A tentative group-contribution approach is next proposed in terms of log P values for the partitioning of a number of neutral molecules between cationic micelles and water. It is shown that the log P group-contribution for various polar moieties follows the same order than that obtained in the two-phase 1-octanol/water binary. The increase of CMC sometimes observed upon addition of small or large neutral solute concentration is interpreted using preferential solvation models.