Surface mixing morphology in bilayer-polymer films

The surface morphology of annealed bilayer films, thin poly(methyl acrylate) (PMA) and/or polystyrene (PS) films on poly(vinylidene fluoride) (PVDF) thick film, was studied on the basis of X-ray photoelectron spectroscopy and atomic force microscopy. Although the surface free energy values for PS and PMA are close, the surface morphology of annealed bilayer films are fairly different due to the difference in the interaction parameter between components of the bilayer film. Ater annealing at above the melting temperature of PVDF, top-layer PMA which is miscible with PVDF in the melt was gradually remixed with bottom-layer PVDF across all the interface, whereas the dewetting of top-layer PS was observed in (PS/PVDF) bilayer film due to the immiscibility and the surface free energy difference beteen PVDF with PS. However, the surface concentration of PVDF was in the order (PMA/PVDF)>[(PMA/PS) mixture/PVDF)] bilayer films under the same annealing condition. This result was explained in terms of the intermolecular interaction, the surface free energy and the competition between wetting and remixing processes.