New insight into adsorption of polymer melts onto impenetrable surfaces

We report the novel structures of irreversibly adsorbed polystyrene (PS) layers composed of six different molecular weights ranging from 30k to 2,000k. Spin cast PS films (originally $\sim $ 100 nm in thickness) prepared onto hydrogen-passivated silicon substrates were annealed at 170 \r{ }C for about 50h under vacuum and subsequently rinsed with toluene (a good solvent for PS) thoroughly. X-ray reflectivity results show that the adsorbed layers are well described by a two-layer model: the one is a higher density layer relative to the bulk adjacent to the substrate and the other is a nearly bulk density layer on top of the bottom layer. On the other hand, a single-layer model with the higher density layer is valid for the adsorbed layers composed of low molecular weights PS. We will reveal the origin of the difference, shedding light on a new pathway for the formation of the equilibrium adsorbed polymer layers at the impenetrable interfaces.