MICELLAR SOLUBILIZATION IN STRONGLY INTERACTING BINARY SURFACTANT SYSTEMS

The apparent partition coefficient P of barbituric acids between micelles and water has been determined in mixed binary surfactant solutions from solubility measurements in the whole micellar composition range. The binary systems chosen ranged from the strongly interacting system dodecyltrimethylammonium chloride + sodium dodecyl sulfate to weakly interacting systems such as benzyldimethyltetradecylammonium chloride + tetradecyltrimethylammonium chloride. In all cases studied, mixed micelle formation is unfavorable to micellar solubilization. A correlation is found between the unlike surfactants interaction energy, as measured by the regular solution parameter 0 and the solute partition coefficient change upon surfactant mixing. By use of literature data on micellar solubilization in binary surfactant solutions, it is shown that the change of P for solutes which are solubilized by surface adsorption is generally governed by the sign and amplitude of the interaction parameter /3. For solutes which are solubilized by penetration in the mixed micelle hydrocarbon core, the solubilization increase observed in all available cases may be interpreted by a Laplace pressure change due to micellar sphere-to-rod transition, which occurs in strongly interacting binary surfactant systems. © 1990, American Chemical Society. All rights reserved.