Re-assembly behaviors of polystyrene-b-poly(acrylic acid) micelles

The re-assembly behaviors of spherical micelles of the polystyrene-b-poly(acrylic acid) (PS-b-PAA) diblock copolymer in different solvent mixtures were investigated using dynamic light scattering, transmission electron microscopy and atomic force microscopy. Depending on the nature of the solvent, PS-b-PAA micelles re-assembled from spheres to nanorings in toluene or to necklace-like aggregates in water induced by solvent evaporation. Systematic studies suggested that the re-assembly behaviors on a neutral surface are strongly correlated with the micellar surface components, the solvent polarity and the chain length of the micelle corona of the solvated blocks. We proposed that the formation of nanorings from PS-b-PAA micelles in toluene is mainly induced by the dewetting process of the solvent, while the necklace-like structure arises from the hydrogen bonding interactions among the partially dissociated PAA units.