Self-assembly of an amphiphilic diblock copolymer in aqueous solutions: Effect of linear charge density of an ionogenic block

Abstract

The effect of linear charge density of the ionogenic block on the selfassembly of the amphiphilic diblock copolymer based on polystyrene and poly(4�vin ylpyridine) partially alkylated by ethyl bromide in aqueous solutions at pH 9 is studied by UV spectrophotometry and dynamic and static light scattering. Dur� ing dispersion in water, the diblock copolymer forms micelles composed of the hydrophobic polystyrene core and the amphiphilic lyophilizing corona consisting of Nethyl�4�vinylpyridinium bromide ionic units and uncharged units of 4�vinylpyridine. It is shown that with a change in the fraction of charged units in the lyo� philizing block from 30 to 90 mol %, the thermodynamic quality of the solvent with respect to micelles is slightly monotonically improved and the hydrodynamic sizes of micelles in 0.05 M NaCl are increased. At the same time, such properties as the weightaverage deg ree of aggregation of macromolecules in a micelle, the dimensions of the corona in 0.05 M NaCl, and the dispersion stability of micelles in aqueous-saline solution abruptly change when the content of charged units in the lyophilizing block is 60-70 mol %. After addition of oppositely charged polyelectrolytes or lowmolecu larmass surfactants into the micellar solution, poly� electrolyte complexes form and the solubility of these complexes in an excess oppositely charged component likewise changes abruptly with variation in the fraction of charged units in the range from 60 to 70 mol %. A qualitative description is advanced to explain the effect of linear charged density of the lyophilizing block on the selfassembly and complexing behavior of diblock copolymers in aqueous solutions.