Dewetting of thin polymer films reveals non-equilibrium conformational difference between substrate and air sides

The anomalous dynamics of thin polymer films, often attributed to geometrical confinement and interfacial interaction, have aroused considerable interest, particularly with regard to the inherent and processing-induced chain conformation changes. Here, the capillary peeling method is employed to obtain reattached thin polystyrene films with either the substrate or the air side beneath. Compared to traditional dewetting experiments solely conducted on the substrate side of as-cast films, the difference in dewetting behavior between the two sides of films is demonstrated, with the air side showing a faster dewetting velocity in the early stage and a larger apparent residual stress. Through this method, the non-equilibrium conformation of polymer chains that used to be located on the air side due to spin-casting can be thoroughly investigated without any interference from free surface effects. Our findings offer evidence of the difference in interfacial chain entanglement density, which determines variations in the performance on relaxation of residual stress within the thin films. This work is an improved method to study polymer dynamics through dewetting and gives insight into chain conformation at interfaces during processing.