The glass transition in two different polymeric systems
Frau Marie-Luise Braatz (TU Darmstadt)

Two different kinds of systems based on the polymer polystyrene were analysed: ultrathin polymer films on different substrates and binary mixtures of the polymer and an organic solvent. For the first set of polymeric systems the focus is on the impact of adsorption on the glass transition of ultrathin films of polystyrene. When annealing these films the forming of an irreversibly adsorbed layer, a so-called Guiselin-brush, is observed. The kinetics of the growth of this layer shows a distinct correlation to the change in the glass transition temperature upon different annealing times. The second set consists of the dynamically asymmetric mixture of polystyrene and the small molecule methyl tetrahydrofurane (MTHF). The blends are fully miscible on supercooling but still exhibit two glass transition temperatures. Between these two temperatures MTHF relaxes in a matrix of polystyrene, showing the signature of geometrical confinement on the nanoscale in its dynamic properties. Among the interesting characteristics observed, is a transition from fragile to strong behavior of the time constants and in some cases features of a type-A glass transition are found.