Effects of Annealing Solvents on the Morphology of Block Copolymer-Based Supramolecular Thin Films

Abstract

We report a strategy that combines supramolecular assembly and solvent annealing to manipulate the microdomain orientation in block copolymer thin films. In supramolecular thin films formed by polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) with 3-pentadecylphenol (PDP) hydrogen-bonded onto P4VP blocks, where PS blocks phase-separate into cylindrical microdomains, we found that the orientation of PS cylinders can be controlled by using different types of solvents to anneal the films. As films are annealed under the vapors of solvents bearing no oxygen atoms, such as chloroform, PS cylinders are perpendicular to the surface, while under those of solvents bearing oxygen, such as THF, PS cylinders are parallel to the surface. Furthermore, the orientation is switchable upon the alternate use of different types of solvents. The 1H NMR measurements showed that the strengths of hydrogen bonds between PDP and P4VP are greatly weakened in oxygen-bearing solvents due to the competition of the highly electronegative oxygen atoms. We thus suggest that the binding capability of PDP onto P4VP is the key to determine whether the supramolecules can be assembled in the vapors of different types of solvents, which in turn, regulates the orientation of PS cylinders.