Morphological Changes in Block Copolymer Thin Films Driven by Complex Coacervation

Block copolymer thin films have been proposed as a method for immobilizing target molecules on a nanostructured scaffold. The use of a charged-neutral block copolymer (BC) enables the incorporation of oppositely charged molecules into thin films of the material. However, incorporation of oppositely charged macromolecules can trigger a phase change via coacervation. In this work, the effect of polyanion strength on the structure of BC self-assembly in thin films is examined. Complexation with the strong synthetic model polyanion, polystyrene sulfonate, leads to precipitation, while complexation with the weak synthetic model polyanion, poly(acrylic acid), leads to micellization. This difference in phenomena is likely driven by the ability of the weaker polyanion to charge modulate. The weakest polyanion tested was a model protein, amylase, which showed a rich set of phase behavior dependent on the blending ratio between the protein and the BC. The protein’s charge density is significantly lower than that of the synthetic polymers, which leads to weaker interactions between the protein and the BC by comparison. As a result, the structure of the BC is less disrupted by the protein than by the synthetic polymers at moderate loading (up to ~30 wt%).