Rapid structural reorganization in thin films of block copolymer self-assembly

In the present study, the thin films of a symmetric polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) were prepared on a neutral substrate and subjected to solvent annealing, sequentially coupled with thermal annealing for a short time. For this process, a P(S-r-MMA)-grafted substrate was used for surface neutrality to the PS and PMMA blocks. During solvent annealing with PMMA-selective acetone vapor, the block copolymer (BCP) films show a predominantly parallel orientation of the cylindrical PS microdomains over the underlying perpendicular PS cylinders on the substrate. Sequential thermal annealing of the BCP films for a short time led to efficient structural reorganization to an equilibrium morphology with the perpendicular orientation of the lamellar microdomains. This approach suggests a simple and useful route for directing the orientation of microdomain arrays in the thin films of BCP self-assembly.