Solubilization of Benzoic Acid Derivatives by Nonionic Surfactants: Location of Solubilizates in Hydrocarbon Core of Micelles and Polyoxyethylene Mantle

Abstract

The micelles that nonionic surfactants containing polyoxyethylene head groups form in aqueous solution have a hydrocarbon core surrounded by a mantle, which can be described as a dense solution of polyoxyethylenes. Solubilization, or the uptake of organic molecules in such micelles, may involve two broadly defined loci: (a) the hydrocarbon core along with its interface, and (b) the polyoxyethylene mantle. It is shown that the solubilization of many benzoic acid derivatives and phenolic preservatives in such micelles can be described in terms of the two loci of solubilization. The relative importance of the two loci can be derived in an approximate fashion from solubilization data in systems where the polyoxyethylene chain length is varied on the basis of two simplifying assumptions. The distribution of the solubilized species between the two loci is related to the chemical structure of the solubilizate, and it is important in understanding the physical and chemical reactivities of the solubilized species.