The Phase Behavior of Polystyrene-b-Poly(2-vinylpyridine) System in Thin Film Geometry

The thickness-dependent phase transitions of polystyrene-block-poly(2-vinylpyridine) (PS-$b$-P2VP) in the films was studied and compared with the melt using small-angle X-ray scattering (SAXS) and grazing incidence small-angle X-ray scattering (GISAXS). The PS-$b$-P2VP melt presented the sequential OOT transitions, composed of hexagonally perforated layer (HPL)-gyroid (GYR)-disordered phase (DIS) with increasing temperature, while the PS-$b$-P2VP films showed a different morphological transition pathway by decreasing film thickness. It was attributed to the film thickness effect of interfacial interactions on the order-to-order transition (OOT) and order-to-disorder transition (ODT) particularly in the 3-dimensional network structure of GYR.