Solvent-induced surface morphology of thin polymer films

With specular and off-specular X-ray scattering the surface morphology in terms of surface roughness, film quality, and roughness correlation in thin polymer films of polystyrene and fully brominated polystyrene is measured. During the preparation of the thin films on top of silicon substrates, the common solvent was varied. We investigated eight different solvents and three different solvent mixtures to depict the influence of typical solvent parameters. In the regime of a small solvent vapor pressure, we observed correlated roughness as the ultimate lower limit of accessible surface smoothness. The resulting films are homogeneous, and the surface roughness is given by the substrate. In an intermediate vapor pressure regime marked surface morphologies are detected, while at a high vapor pressure smoother films result again.