Molecular weight dependence of mean square displacement in ultrathin polymer films as studied by inelastic neutron scattering

Abstract

In previous papers, we found that the mean square displacement u2 in polystyrene thin films decreased with film thickness and discussed two possible causes for the decrease. One is the hard interface layer between the polymer thin film and the substrate, and the other is the spatial confinement effect of polymer chains. In order to disclose the cause of the decrease of u2 with film thickness, we studied the molecular weight Mw dependence of u2 in polystyrene thin films. We found that u2 was independent of Mw within experimental error, concluding that the interface effect is a main reason for the decrease of u2 with film thickness.