Probing Chain Orientations in Block Copolymer Thin Films with Polarized Soft X-ray Scattering

Block copolymers (BCPs) self-assemble into periodic morphologies with length scales between 5-100 nm, with the presence of the interface between components implying a degree of preferential orientation of the polymer chains. Characterizing the chain orientation will provide important insights into the self-assembly of BCPs, particularly as higher χ systems begin to play an important role in applications such as directed self-assembly. However, experimental characterization of molecular orientation distributions in amorphous soft matter remains a significant challenge. Polarized soft X-ray scattering (P-RSoXS) utilizes the interactions of soft X-rays with molecular dipoles to provide a probe of molecular orientation in organic materials. P-RSoXS measurements were conducted on a series of thin films of lamellar polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA), and evidence for molecular orientation in those films was observed in the scattering patterns near the absorption peaks for both the aromatic rings in PS and the carbonyl bond in PMMA. These scattering patterns are fit with a data fusion approach that combines real space information about the composition distributions with a series of candidate orientation functions in order to extract quantitative orientation distributions.