Controlling Ordered Structures of PS-b-P2VP Block Copolymer Thin Film by Tuning Solvent Evaporation Rate

Selective solvents for each block were chosen to induce specific blocks of the Polystyrene-block-poly(2vinylpyridine) (PS-b-P2VP) block copolymer (BCP) thin film with the purpose of comparing the degree of block swelling affected by solvent vapors onto the thin film. Solvents with high boiling point have been preferred for this study, because these solvents evaporate slowly, and allowing the block copolymer to self-assemble properly. Toluene and acetic acid were considered as suitable solvents for polystyrene (PS) and poly(2vinylpyridine) (P2VP), respectively. We prepared 1 wt% PS-b-P2VP BCP (79.0k-b-36.5k kg/mol) solution in a mixed solvent of toluene and tetrahydrofuran (THF) with a ratio of 7:3. Then, applied solvent annealing to the thin films with toluene and acetic acid at 21 degrees C for 3 hours, 6 hours and 9 hours. Thermal annealing to the thin films at 80 degrees C, 100 degrees C, 150 degrees C, 200 degrees C and 250 degrees C for 24 hours was also applied. The morphology of the resulting thin film has been characterized using the atomic force microscopy (AFM). The formation of the block copolymer structure on thin film revealed highly affected by the evaporation rate owing to the decreased polymer mobility occurred by lower temperature of the solvent with high boiling point.