and Atsushi Takano

Depth distribution of different solvents in a phase-separated block copolymer thin film

The structural change induced by the contact with different solvents was investigated for a diblock copolymer thin film, of polystyrene (PS) and poly(2-vinylpyridine) (P2VP), forming a lamellar structure by in-situ neutron reflectometry with a conventional cell for the measurement on solid/liquid interfaces. In the case of methanol, which is a selective solvent for P2VP, the structural change was induced by the penetration of methanol into the film, and the original lamellar structure was almost recovered by drying the film even after the solvent contact. On the other hand, when toluene was used as a selective solvent for PS, the block copolymer thin film was easily dissolved into toluene, and its original state was never recovered after the solvent contact. Further, water induced the structural change in the block copolymer thin film similarly to methanol, though it is a poor solvent common for PS and P2VP.

In-Situ Reflectometry Observation on Structural Changes of Thin Self-Assembled Block Copolymer Films

The structural changes induced by solvent contact or heating were observed for thin spin-coated polystyrene-block-poly(2-vinylpyridine) diblock copolymer (PS-P2VP) films using in-situ neutron reflectivity and grazing-incidence small-angle X-ray scattering (GISAXS) techniques. The lamellarly-ordered PS-P2VP film showed some structural changes in contact with water though it is a poor solvent for both the component polymers, while the original structure was recovered after drying the film. When toluene was used as a selectively good solvent for PS, the thin film was dissolved into the solvent. On the other hand, the thin as-prepared PS-P2VP film with spherical microdomains exhibited laterally a pair of scattering spots symmetrical relative to the specular reflection ridge in the GISAXS pattern, indicating the existence of some lateral structural correlation in the film. On a temperature jump up to 200 °C, these two scattering spots started to disappear around the glass transition temperature, and then almost completely vanished at 200 °C unexpectedly though the PS-P2VP used here should be kept in the strong-segregation state. The spherical structure could be completely disordered or kept ordered but with lateral distortion in its orientation. Being cooled down to a room temperature again, the two scattering spots were recovered, and became more intense with their position shifting slightly to lower QY-region than before heating due to the improvement in ordering.