Effect of mechanical confinement on an immiscible polymer-polymer interface

The interfacial width formed between two immiscible polymers when they are subject to mechanical confinement has been studied using the neutron reflection technique. Deuterated polystyrene (dPS) and high-density polyethylene (HDPE) of high molecular weight were used in this study. The measurements were performed in situ at 175°C using a melt cell where the thickness of the dPS layer, coating the silicon substrate, was varied and was held onto a thick HDPE plate. The interfacial roughness extracted from the reflectivity curves was around 1.5 nm for thicker dPS films and decreased to around 1.1 nm for thinner film. In contrast to the prediction that long range van der Waals forces would destabilise the system, particularly for the thinner dPS films, it is stable within the time scale of the measurements. This could indicate a possible mechanical confinement effect on the stability of thin polymer films.