Phase decomposition in polymer blend films cast on substrates patterned with self-assembled monolayers

Abstract

Thin polymer films with lateral structures are expected to play an important role in future applications (e.g. plastic-based electronic devices). Such structures could be formed when blend films are spun-cast onto substrates patterned with self-assembled monolayers (SAM). The spin-coating process results in composition variations accompanied by surface undulations. We have studied both phenomena for PVP/dPS and PVP/PBrS blends, composed of poly(vinylpyridine) (PVP) and deuterated (dPS)- or brominated (PBrS)-polystyrene. SAM stripes of HS(CH2)15CH3 on Au substrate (‘bare’ or covered with HS(CH2)15COOH) were used as the pattern with periodicity of 4μm. Transfer of the pattern from the substrate to the film interior and to the film surface was examined with secondary ion mass spectroscopy (SIMS) and atomic force microscopy (AFM) combined with selective dissolution of blend components. Characteristic size D of the phase domains corresponding to given spin-casting conditions was determined for the blends cast on homogeneous SAM substrate. Fourier transform analysis (FTA) of topographic (AFM) and compositional (SIMS) maps was performed. FTA confirms that the pattern-directed composition variations coincide with the surface undulations. It reveals also that most effective pattern transfer is achieved for the size D commensurate with the pattern periodicity for the carefully adjusted polymer–substrate interactions.