Roughness correlation and interdiffusion in thin films of polymer chains

The surface morphology of thin bilayer polymer films on top of glass substr ates was investigated. The bilayer consists of a blend film of protonated a nd deuterated polystyrene and an underlying deuterated polystyrene film. Ch oosing the thickness of the top film larger than 8 times and smaller than 2 times the radius of gyration of the chains enables the determination of fi lm thickness and confinement effects. With diffuse neutron scattering at gr azing incidence in the region of total external reflection, a depth sensiti vity and a contrast even at the internal polymer-polymer interface was achi eved. The underlying film is conformal to the substrate, and depending on t he thickness of the top film two different types of roughness correlations are observed. Thin confined films nestle to the underlying polymer films, w hile the stiffness of thicker bulky films provides an independent morpholog y. In both cases, annealing above the glass-transition temperature yields a n interdiffusion at the internal polymer-polymer interface, and the polymer -air surface remains essentially unchanged with respect to roughness correl ations. (C) 1999 John Wiley & Sons, Inc.