Complexation of a Polyelectrolyte Brush with Oppositely Charged AB Diblock Copolymers: The Zipper Brushes

The internal stratification of a polyelectrolyte complex (zipper brush) formed by mixing of an anionic charged polyelectrolyte brush (PEB) with cationic-neutral diblock copolymers bearing a very long neutral block is studied by means of molecular dynamics simulations. The authors find that the fraction of the neutralized PEB units in the mixture increases as the fraction of the PEB charged units (a) increase for high grafting densities (d). Due to the charge neutralization condition, from the initial PEB through the complexation with the appropriate choice of a cationic-neutral copolymer, neutral brush having grafting density lower, equal, or much higher than that of the PEB are obtained. The addition of monovalent salt in the mixture with concentrations 0.1 and 1 m leads to a reduction in complexed diblock copolymer chains of up to 91% and practically the initial PEB is recovered. The findings are in full agreement with existing experimental predictions and provide new insights into the structure and the shape of the coacervate. The latter progressively changes from a dense film to perforated film, to lamella, to pinned micelles, to stacks as a, d, and the molecular weights of the PEB and diblock copolymer blocks are altered.