Direct imaging of surface and bulk structures in solvent cast polymer blend films

We have used laser confocal fluorescent microscopy and atomic force microscopy to study surface and bulk morphologies in solvent cast polydnethyl methacrylate) (PMMA)/polystyrene (PS) films. The solvent evaporation rate strongly affects the surface morphology. Sufficient suppression of solvent evaporation results in a periodic distribution of highly monodisperse PMMA-rich domains. Formation of the surface pattern is interpreted in terms of diffusion-driven coarsening of the minor phase and flow induced by the diffusive transport of PMMA molecules from the bulk of the liquid film to the air-film interface.