Time-Dependent Behavior of Block Polyelectrolyte Micelles in Aqueous Media Studied by Potentiometric Titrations, QELS and Fluorometry

Block polyelectrolyte samples containing long hydrophobic blocks, e.g., polystyrene, and long polyelectrolyte blocks, e.g., poly(methacrylic acid), do not dissolve in aqueous media. However, multimolecular micelles consisting of compact polystyrene cores and polyelectrolyte shells may be prepared by dialysis from organic solvent−water mixtures into aqueous buffers. Polystyrene cores are kinetically frozen in water and the behavior of the micellar systems is determined by the polyelectrolyte behavior of the shell. Poly(methacrylic acid) does not represent a typical polyelectrolyte. Due to the presence of a strongly hydrophobic methyl group in each repeating unit, its behavior more resembles that of a polysoap. In aqueous micellar systems, poly(methacrylic acid) chains form a fairly compact hydrophobic layer close to the core/shell interface. In our recent works, we have found that the state of the inner part of the shell responds rather slowly to shock changes in the bulk pH and the ionic strength of the solution. In this work, we use a combination of potentiometry, QELS, and fluorometry to study the time-dependent behavior of polyelectrolyte micellar shells.