Dresden 2011 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 13: Focused Session: Confinement of Polymers in Nanoscopic Layers - How Much do Properties Change? I

CPP 13.3: Invited Talk

Tuesday, March 15, 2011, 11:30–12:00, ZEU 160

On the origin of the deviations from bulk behavior in ultrathin polymer films: from glass transition to tracer diffusivity — •Simone Napolitano, Michael Wübbenhorst, and Cinzia Rotella — Department of Physics and Astronomy, Katholieke Universiteit Leuven, Celestijnenlaan 200D, Leuven, 3001, Belgium

We show clear evidence that the changes ultrathin films undergo during annealing are strongly correlated to the amount of chains irreversibly adsorbed at the interface. An analysis of the time evolution of the dielectric function during annealing steps above Tg revealed three different regimes: at times much shorter than the adsorption time, the thickness of the adsorbed layer is constant and the incomplete interface mimics the effect of a free surface (packing frustration); upon increase of surface coverage, the films undergo a series of metastable states characterized by the largest changes in the deviations from bulk behavior; finally the system approach a new equilibrium whose properties are fixed by the new interfacial configurations. Our picture is confirmed by further investigation of the distribution of glass transition temperatures, tracer diffusivity and dielectric relaxation strength at different distances from the adsorbing interface. We show that during annealing ultrathin films evolve towards a steady state whose properties might still differ from bulk. In particular, for polystyrene, the lack of specific interactions with the substrate results in slow adsorption kinetics, keeping the deviations from bulk behavior in steady states with an extremely long lifetime.