| 초록 |
Block copolymers such as polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA), polystyrene-b-poly(vinyl pyridine) (PS-b-PVP) thin films with various initial thicknesses are known to show the unusual hierarchical structures (i.e., island-on-island or hole-in-hole). The development of hole-in-hole structures turns out to be initiated by the lateral strain due to the evaporation of a small amount of residual solvent after the fast formation of parallel lamellar. In particular, for both PS-b-PMMA and PS-b-PVP thin films, intriguing fractal holes were observed presumably due to the different affinity between block copolymer of bottom layer and substrate. Surface morphology was investigated by combining optical microscopy (OM) and atomic force microscopy (AFM) and our experimental results reveal three kinds of fractal holes, (i.e., fractal hole-in-hole, hole-in-fractal hole and fractal hole-in-fractal hole) depending on initial thickness. Combinatorial method by varying the film thickness was carried out to examine key factors for different shape of hierarchical structure. In addition, the effect of interaction between bottom layer polymer and substrate was discussed using PS surface grafted substrates prepared by ATRP (Atomic Transfer Radical Polymerization). |
