Morphology of Semicrystalline Diblock Copolymer Thin Films upon Directional Solvent Vapor Flow

The possibility of achieving templates of highly ordered nanostructures with crystalline nano-objects embedded inside an amorphous matrix is addressed. Atomic force microscopy and grazing incidence small-angle X-ray scattering (GISAXS) are used to probe the morphology at the surface and inside thin films of the diblock copolymer polystyrene-block-poly(ethylene oxide) P(S-b-EO). Directional benzene vapor flow introduces the orientation of poly(ethylene oxide) (PEO) cylinders inside the PS matrix. Within a limited film thickness regime, the cylinders are oriented parallel to the sample surface in domains of several micrometers due to shearing effects caused by the flow of benzene vapor parallel to the polymer surface. The crystallization of the PEO block by the benzene vapor treatment is also observed and crystals with sizes that approach that of the confined PEO domains are formed. Perpendicular orientation of the PEO crystalline stems with respect to the PEO cylindrical nanodomains is deduced from grazing incidence X-ray diffraction. X-ray reflectometry and scanning electron microscopy complement the investigation.