We have studied the dynamics of dewetting at the interface between polystyrene (PS) and poly(methyl methacrylate) (PMMA) as a function of the molecular weights of the two materials. Optical microscopy and atomic force microscopy have been used to follow the dewetting process and to image both the surface and interfacial structure in the vicinity of the growing holes. We determined the scaling behavior of the dewetting velocity as a function of the molecular weight of the dewetting species (PS). Different regimes are found depending on the PMMA molecular weight. For large PMMA molecular weights the dewetting velocity scales inversely with the PS viscosity, while for low PMMA molecular weights, the dewetting velocity is almost independent of the PS viscosity. The experimental data are in quantitative agreement with recent theoretical predictions.

We have measured the Flory−Huggins interaction parameter (χ) for blends of polystyrene (PS) and poly(4-vinylpyridine) (P4VP) by three different methods. First, we measured the micelle spacings in microphase-separated films of PS−P4VP diblock copolymers by secondary ion mass spectrometry and atomic force microscopy. Second, we measured the contact angle of droplets of homopolymer PS on P4VP homopolymer film. Finally we determined the interfacial width between homopolymer layers of dPS and P4VP by neutron reflectometry. From each of these experiments χ was calculated using mean field theory in the strong segregation limit. These values of χ are much larger than those of other nonionic polymer pairs. We discuss the importance of this findings.