Spatial Heterogeneity of Glassy Polymer Films

By studying the morphology of polystyrene films subjected to a fast structuration method, we demonstrate the spatial heterogeneity of their surface viscoelasticity at temperatures well below the glass transition temperature, Tg. Our results point to a nonrandom arrangement of zones of different elastic modulus deep in the glassy state. The spatial distribution of viscoelastic properties of the film was temperature dependent; we observed the presence of soft zones (surrounded by areas of larger elastic modulus) spanning increasingly larger areas of the surface as T gets closer to Tg. The heterogeneity on viscoelastic properties of the film is supported by the temporal evolution and relaxation of the structured surfaces and by direct measurements of the spatial distribution of the local elastic modulus of polystyrene films.