Untersuchungen des Oberflächenglasüberganges von Polystyrol mittels des Einbettens von Edelmetall-Clustern
The temperature dependent embedding process of noble metal nanoclusters into polymers was used to probe the surface glass transition. X-ray photoelectron spectroscopy (XPS) was applied to study the embedding of Au nanoclusters into polystyrene. A small decrease of glass transition temperature (Tg) at the surface compared to the bulk, which decreases at low Mw, was detected with this method. In order to understand the Tg depression in monodisperse polystyrenes measurements were performed on bimodal mixtures of monodisperse polystyrenes. The results on the bimodal mixtures rule out the interpretation that the Tg depression at the surface is due to an enrichment of shorter chains. Transmission electron microscopy (TEM) investigations yield the same cluster sizes and densities for a height and a low molecular weight. Therefore, probe size effects can be excluded. The Tg of thin PS films was additionally determined by the charging and discharging during XPS measurements.