Crystal-like Complex Formation with Binary Charged Block Copolymer Micelles in Dilute Aqueous Media

The morphology of charged block copolymer micelle (BCM) complexes, consisting of polystyrene-\textit{block}-poly(acrylic acid) (PS-$b$-PAA) and polystyrene-\textit{block}-poly(4-vinyl pyridine) (PS-$b$-P4VP) micelles, was controlled by pH of aqueous solvent as well as solvent quality. To determine the effective pH range for the inter-corona combination of PAA and P4VP blocks in aqueous media, we studied the dissociation behavior of both coronas using Fourier Transform Infrared Spectroscopy. Lower pH region (pH\textless 5.0) in aqueous media offers stronger interactions between oppositely charged corona blocks, resulting in polymeric hexagonal prism complexes. In the higher pH region (pH\textgreater 5.5), they first self-assembled into hierarchical spheres induced by the simple adsorption of small PS-$b$-PAA BCMs on the surfaces of PS-$b$-P4VP large compound micelles since the degree of ionization of P4VP blocks is relatively low. However, the crew-cut BCM complex morphology with high aggregation number does not allow the hexagonal prism structure to be formed without rearranging strongly aggregated core blocks. We note that the crew-cut BCM complexation in higher DMF content of a mixed solvent induces inter-corona association leading to the hexagonal prism structure due to the decrease in selectivity of water for PS blocks.