Substrate-induced phase transitions in thin films of cylinder-forming diblock copolymer melts

Terrace formation and morphological behavior in thin films of polystyrene-block-polybutadiene block copolymer have been studied on two chemically different substrates by means of scanning force microscopy. Cylinders parallel to the film plane (CII) are found on weakly interacting substrates in up to five-layer-thick films. A bottom layer of half cylinders is stabilized at the substrate. On strongly interacting substrates, the development of the CII microdomains and nonbulk perforated lamella (PL) and lamella (L) phases depends on the local film thickness. The sequence of structures at transition thickness (in between the steps) suggests a few percent increase of the characteristic microdomain spacing in the order C II-PL-L. Comparison of the interlayer distances on the two types of substrates points to lamella-like structures in bulk of the films on strongly interacting surfaces. © 2006 American Chemical Society.