Modifying Surface Fluctuations of Polymer Melt Films with Substrate Modification

Deposition of a plasma polymerized film on a silicon substrate changes surface fluctuations of a sufficiently thin, glass-forming film on the substrate. X-ray photon correlation spectroscopy measurements show that the surface fluctuations on a 43 nm thick melt film of 131 k linear polystyrene (PS) on a silicon wafer can be described using a hydrodynamic continuum theory (HCT) that assumes the film is characterized by the bulk viscosity. When a plasma polymerized layer is placed on the silicon wafer, the same is seen for a 43 nm film. However, when film thickness is reduced to 32 nm, the fluctuations are slower than predicted by the HCT. The confinement effect for PS on silicon is larger than that for PS on the plasma polymerized film. We attribute this to the variation in the thickness of a bound layer at the substrate with the surface chemistry of the substrate. Use of the Advanced Photon Source at Argonne National Laboratory was supported by the DOE's Office of Science under Contract DE-AC02-06-CH11357. DoD funding provided through the TCC ({\#}FA7000-14-2-20016).