Viscoelastic measurements in thin polystyrene melts as derived from scanning force microscopy-induced nanoflow patterns

The response of a thin-film polystyrene melt to a raster-scanned SFM tip was investigated. At high temperatures the scanning process induced intricate pattern formation whose quantitative characteristics were compared as a function of tip trajectory, temperature, and scan rate Analysis of the images revealed that the features are strongly correlated with the geometry of the raster scan pattern. The dependence of the patterns on temperature and scan rate was consistent with time-temperature superposition as described by the Williams-Landel-Ferry (WLF) equation. WLF analysis implies an increased glass transition temperature derived from elevated pressure beneath the tip. The latter provides an estimate of the radius of the affected film region near the tip.