Thermodynamic Study of the Solubilization of Crown-Substituted Magnesium Phthalocyaninate in Aqueous Solutions of Cationic Surfactants

Abstract

Solubilization of crown-substituted magnesium phthalocyaninate(I) has been studied by spectrophotometry in aqueous solutions of tetradecyltrimethylammonium(II), hexadecyltrimethylammonium(III), and hexadecyltriphenylphosphonium bromides. The experiments have been carried out with saturated solutions of I occurring at the thermodynamic equilibrium with its precipitate. The experimental data have been used to determine the following thermodynamic characteristics of the solubilization: the solubilization capacity of micelles, the coefficient of solubilisate partition between micelles and an ambient solution, and the standard solubilization affinity of I. It has been shown that, in spite of different structures of the surfactants, the standard works of a I molecule transfer to micelles of all three surfactants are almost equal. The found values of the solubilization capacity, as calculated per one molecule of I, in micelles of II and III lead to abnormally large aggregation numbers. This fact may be explained by possible development of a bimodal distribution of micelles, at which solubilisate-containing micelles coexist with “empty” micelles; as a result, the average number of solubilisate molecules in a micelle may appear to be smaller than unity.