Using block copolymerself-assembly to imprint the crystallization of polymer dendrites

Abstract

We utilize the self-assembly of cylinder-forming block copolymer (BCP) films to create templates for dendritic polymer crystallization patterns. This templating was achieved by simply spin-casting thin films from a solution containing both the BCP [polystyrene-block-poly(ethylene oxide) (PS-b-PEO)] and a homopolymer (polyethylene oxide) under controlled vapor atmosphere conditions, without the need for any additional processing (e.g.solvent or thermal annealing). The BCP first organized into a hexagonal array of vertically oriented PEO cylinders that served to template dendritic PEO homopolymer crystals on the surface of the BCP pattern. No surface defects such as dewetting holes or macroscopically phase-separated domains were observed on top of the BCP film. We find that the PEO dendrites crystallized on this BCP template exhibit a periodic height undulation pattern on their surface. The undulation pattern directly reflects the hexagonal pattern symmetry and associated height undulations of the BCP underneath these crystals. The formation of this hierarchically organized polymer crystallization morphology illustrates how one self-assembly can be used as a template to control the organization of another self-assembly process—a fabrication strategy of potentially great significance in the programming of complex structures using self-assembly.