Molecular aggregation states of poly{2-(perfluorooctyl)ethyl acrylate} polymer brush thin film analyzed by grazing incidence X-ray diffraction

Fluoropolymer brush with crystalline side chains was prepared by surface-initiated atom transfer radical polymerization of 2-(perfluorooctyl) ethyl acrylate (FA-C₈) from a flat silicon substrate. The crystallization and the molecular aggregation structures of polymer side chain at the outermost surface and internal region in the brush film were characterized by grazing incidence X-ray diffraction (GIXD) measurement using two different incident angles of X-ray. At the air interface of PFA-C ₈ brush film, the rod-like R_f group was oriented perpendicular to the surface forming a hexagonal packing structure to reduce surface energy. In contrast, the oriented R_f groups parallel to the substrate coexisted at the internal region in the brush. This unique depth dependence of crystalline state of the fluoropolymer brush was observed by surface-sensitive GIXD measurement.