Using Block Copolymer Self-Assembly to Imprint the Crystallization of Polymer Dendrites
Sangcheol Kim, Alamgir Karim, Jack F. Douglas, Christopher L. Soles, R M. Briber
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) or (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 where no surface defects such as dewetting holes or macroscopically phase-separated domains were observed. We find that the PEO dendrites forming on this BCP template exhibit a periodic height undulation pattern on their surface that directly reflects the hexagonal BCP pattern and height undulations underneath these crystals. The formation of this hierarchically-organized polymer crystallization morphology illustrates how self- assembly can be used as a template to control the organization of other self-assembly processes- a fabrication strategy of potentially great significance in the programming of complex structures using self-assembly.