Influence of Temperature and Type of Solvents on the Microdomain Orientation of PS-b-P2VP Ultrathin Films by Solvent Annealing

The effect of temperature and type of solvent on the microdomain orientation during solvent-annealing of block copolymer ultrathin films on silicon substrates was investigated using asymmetric polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) diblock copolymer. When the solvent-annealing was performed with THF at 20 degrees C, the ultrathin film exhibited a mixed orientation of cylinders parallel and perpendicular to the substrate while at 25 degrees C only parallel cylinders were observed by AFM. The solvent annealing with acetone gave a dot pattern at 20 degrees C and a line pattern at 25 degrees C. On the other hand, in the case of solvent-annealing with toluene perpendicular cylinders were observed at 25 degrees C while at 20 degrees C the morphology was not clear. The orientation and morphology of microdomains as well as the kinetics in PS-b-P2VP ultrathin films on solvent-annealing is significantly affected by temperature and type of solvent. By controlling temperature and selecting the solvent, perpendicular cylinders can be formed predominantly on the substrates.