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

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.