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We demonstrate using neutron reflectometry that the internal interfaces in a trilayer system of two identical thick polystyrene layers sandwiching a much thinner (deuterated) poly(methyl methacrylate) layer 15 nm thick (viscosity matched with the polystyrene layers) increase in roughness at the same rate. When the lower polystyrene layer is replaced with a layer of the same polymer of much greater molecular mass, two different growths of the interfaces are observed. From the growth of the interface for this asymmetric case in the solid regime using the theoretical prediction of the spinodal instability including slippage at the interface, a value of the Hamaker constant of the system has been extracted in agreement with the calculated value. For the symmetric case the rise time of the instability is much faster.

International audience; We use optical and scanning force microscopy to explore the possibility of switching the stabilityof a bilayer of poly(methyl methacrylate) (PMMA) on polystyrene by simply changing the filmthickness. We show that for thin PMMA layers on thicker polystyrene films, the PMMA layer isunstable to thickness fluctuations. However, polystyrene layers are unstable when they are substantially thinner than the now stable PMMA film. Dewetting morphologies are catalogued as afunction of the thickness of individual polymer layers by identifying which layer is unstable by whichmechanism, be it spinodal dewetting or heterogeneous thermal nucleation. Our results are in goodagreement with a linear stability analysis of the influence of long-range dispersion forces, but alsoindicate the influence of film preparation and small variations of material properties.

We have used off-specular neutron reflectometry to study the rupture of a thin, deuterated polystyrene layer confined between a silicon substrate and a thick poly(methyl methacrylate) upper layer. After total rupture of the buried layer, the resulting roughness at the interface that controls the total reflection edge gives rise to Yoneda off-specular scattering. This hypothesis is confirmed by specular reflectivity data that can be fitted to an effective error function subsequent to the rupture of the buried layer. The observed increase in the Yoneda peak intensities, integrated along the path of constant momentum transfer qz, can be directly related to the formation of an interdigitated structure upon rupture of the buried layer. A distorted-wave Born approximation is used to quantitatively simulate the form of the off-specular data in terms of an equivalent error function, with fitting parameters in good agreement with the physical properties of the samples and key experimental results.