Nanoscale localization of poly(vinylidene fluoride) in the lamellae of thin films of symmetric polystyrene-poly(methyl methacrylate) diblock copolymers

We employed thin film blends of diblock copolymers with functional homopolymers as a simple strategy to incorporate organic functional materials into nanodomains of diblock copolymers without serious synthesis. A blend pair of polystyrene-poly(methyl methacrylate) (PS-PMMA) diblock copolymers and poly(vinylidene fluoride) (PVDF) was selected as a model demonstration because PVDF is a well-known ferroelectric polymer and completely miscible with amorphous PMMA. Thin films of symmetric PS-PMMA copolymers provided the nanometer-sized PMMA lamellae, macroscopically parallel to the substrate, in which PVDF chains were dissolved. Thus, amorphous PVDF chains were effectively confined in the PMMA lamellae of thin film blends. The location of PVDF chains in the PMMA lamellae was investigated by the dependence of the lamellar period on the volume fraction of PVDF, from which we found that PVDF chains were localized in the middle of the PMMA lamellae. After the crystallization of PVDF, however, some of PVDF migrated to the surface of the film and formed small crystallites.