Berlin 2008 – scientific programme

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DF: Fachverband Dielektrische Festkörper

DF 6: Glasses I (joint session DF/DY)

DF 6.1: Invited Talk

Tuesday, February 26, 2008, 09:30–10:00, EB 407

Glass freezing in confined geometries studied by DMA — •Wilfried Schranz, Johannes Koppensteiner, and Madalina-Roxana Puica — Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Wien, Austria

Dynamics in confined surroundings appears in many fields, i.e. in chemistry, physics, biology, material science, etc. Using a dynamic mechanical analyser (DMA) we measured [1] the low frequency elastic response of the glass former salol confined in silica based nanoporous media of various pore sizes (2.5nm to 7.5 nm). In addition to the glass transition of the bulk material of salol we find a second freezing process, showing up in the real and imaginary parts of the complex elastic response. This is explained by a radial distribution of Vogel-Fulcher temperatures inside the pores, an assumption which is consistent with recent computer simulations [2] showing an increase of the molecular relaxation time with decreasing distance from rough pore surfaces. The observed glass transition temperatures decrease with decreasing pore size. The mechanism of the glass transition reduction will be discussed. Acknowledgements: Support by the Austrian FWF (P19284-N20) and the University of Vienna (IK 1022-N) is gratefully acknowledged.

[1] W. Schranz, M.R. Puica, H. Kabelka and A.V. Kityk. Europhys. Lett. 79, 36003 (2007) [2] P. Scheidler, W. Kob and K. Binder, Europhys. Lett. 59, 701 (2002).