Structural transformations of charged spherical surfactant micelles upon solubilization of water-insoluble polymer chains in salt-free aqueous solutions

Abstract

The structural transformations of charged spherical surfactant micelles of potassium oleate upon solubilization of water-insoluble polymer poly(4-vinylpyridine) were studied in salt-free aqueous solutions by several complementary techniques including SANS with contrast variation, NMR (1H and 2D 1H NOESY) spectroscopy, dynamic light scattering, cryo-TEM, and fluorescence spectroscopy. By SANS it was shown that solubilization of polymer in the micelles results in the formation of complexes with necklace structure, where the mean distance between the micelles bound to polymer (beads) is governed by electrostatic repulsion between them. The polymer penetrates deep into the hydrophobic core of the beads and occupies ca. 60% of their volume. As a result, the average number of surfactant ions in the micelles decreases from 60 till 20. The bound charged micelles impart water solubility to the polymer-surfactant system, and it behaves like a polymer coil in a thermodynamically good solvent.