Re-assembly behaviors of block copolymer micelles on substrates: effects of block length and interaction force

Abstract

The re-assembly behaviors of amphiphilic polystyrene-b-poly(acrylic acid) (PS-b-PAA) diblock copolymer micelles were investigated using dynamic light scattering, transmission electron microscopy, and atom force microscopy. PS-b-PAA diblock copolymer self-assembled into spherical micelles with PS as shell and PAA as core in toluene. The micelle size increased with the PS block length in polymers containing a constant length of PAA block. With the PS block length increased, spherical micelles re-assembled various distinguished morphologies such as clusters, large compound micelles (LCMs), rings, and ribbon-like aggregations. In addition, the interaction forces between PS and different substrates were directly measured in toluene to further investigate the mechanism. The results indicated that the re-assembly occurred easily when the interaction force was weak. Systematic studies suggested that the micellar re-assembly behaviors on a flat surface were strongly dependent on the block length and interaction between micelles and substrates. Delineation of these rules provides a novel pathway to the design of hierarchical materials.