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A New Type of Micelles and Concentration of Monomerization for Phthalocyanines in Aqueous Surfactant Solutions
Doklady Physical Chemistry  (IF0.638),  Pub Date : 2021-02-14, DOI: 10.1134/s0012501620120027
A. I. Rusanov, T. G. Movchan, E. V. Plotnikova

Abstract

The existence of a special type of surfactant micelles formed on the solubilization core of phthalocyanine at concentrations significantly below the critical micelle concentration (CMC) has been established. This discovery overturns the traditional concepts of colloidal chemistry, which imply that the surfactant micelles are first formed, and then solubilization occurs in them above the CMC. In the process of solubilization, phthalocyanines (usually existing in an aqueous solution in the form of dimers) undergo monomerization, which is crucial for the manifestation of the functional properties of their molecules. Here, the spectrophotometric study of crown-substituted magnesium phthalocyaninate (I) in an aqueous solution of sodium dodecyl sulfate (II) is reported. It has been found that specific micelles of II (they can be called proto-micelles) involving dimers of I are formed significantly below the CMC. The solubilization capacity of micelles determined from experimental data leads, as calculated per molecule of I in a micelle, to an abnormally large aggregation number (309). This phenomenon can be explained by the formation of a bimodal distribution of micelles, in which micelles with solubilizate coexist with “empty” micelles, so that the average number of solubilizate molecules in a micelle can be less than unity.