Transition behavior of asymmetric polystyrene-b-poly(2-vinylpyridine) films: A stable hexagonally modulated layer structure

•Phase transitions in the bulk and films of asymmetric polystyrene-b-poly(2-vinylpyridine).•Significant change in transitions of the films with decreasing film thickness.•New observation of hexagonally modulated layer (HML) morphology in film geometry.•A stable HML structure extended over the entire temperature range in the films ≤10Lo.

The phase transitions in the films of an asymmetric polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) were investigated by grazing incidence small-angle X-ray scattering (GISAXS) and transmission electron microscopy (TEM). Compared with the sequential transitions in the bulk, hexagonally perforated layer (HPL) - gyroid (GYR) - disorder (DIS) upon heating, the transitions in film geometry were dramatically changed with decreasing thickness due to the growing preferential interactions from substrate, resulting in a thickness-dependent transition diagram including four different morphologies of hexagonally modulated layer (HML), coexisting (HML and GYR), GYR, and DIS. Particularly in the films ≤10Lo, where Lo is d-spacing at 150 °C, a stable HML structure was identified even above the order-to-disorder transition (ODT) temperature of the bulk, which was attributed to the suppressed compositional fluctuations by the enhanced substrate interactions.

Graphical abstractDownload full-size image