Self-Assembly of Block Copolymers with a Strongly Charged and a Hydrophobic Block in a Selective, Polar Solvent. Micelles and Adsorbed Layers

The aggregation of diblock copolymers consisting of a neutral block (A) and a polyelectrolyte block (P) in aqueous salt solution, a precipitant for the A block, is examined using a scaling model. Two self-assembled structures are discussed: micelles and adsorbed layers, as well as the equilibrium between them. The salt concentrations considered are moderately high, so that the electrostatic persistence length of the charged block is smaller than the range of excluded volume correlations. The aggregation number of micelles and the surface density adsorbed layers were found to increase, and the charged block thickness to decrease, with salt concentration. Micellar phase properties are predicted to be similar to those of neutral copolymers in nonpolar solvents. Layers adsorbed from dilute copolymer solutions, below the critical micelle concentration, obtain a higher surface density than layers at equilibrium with micellar solutions. The thickness of the charged block was found to be similar, in the latter case, to that of the micelle corona.