Berlin 2008 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 8: POSTERS Dynamics and Diffusion
CPP 8.9: Poster
Montag, 25. Februar 2008, 16:45–19:00, Poster A
Phase diagram of octylcyanobiphenyl confined to molecular sieves with hexagonal pore structure — Ligia Frunza1, Stefan Frunza1, Hendrik Kosslick2, and •Andreas Schönhals3 — 1National Institute of Materials Physics, R-077125 Magurele, Romania — 2Leibniz Institute for Catalysis at the University of Rostock, D-18059 Rostock, Germany — 3Federal Institute for Materials Research and Testing (BAM), 12205 Berlin, Germany
The molecular dynamics of octylcyanobiphenyl (8CB) confined inside the pores of a series of AlMCM-41 samples with long range ordered structure, constant composition (Si/Al=14) but different pore sizes (between 2.3 and 4.6 nm diameter) was investigated by broadband dielectric spectroscopy (10 mHz to 1 GHz) in a large temperature interval. The filed molecular sieves show two relaxation processes: one has a bulk-like behavior and is due to the 8CB molecules in the pore centers. The second relaxation process is due to the dynamics of the molecules in a surface layer. The corresponding relaxation time is ca. two decades slower than that of the first one. Its temperature dependence obeys the Vogel/Fulcher/Tammann (VFT) characteristic for glassy dynamics. The characteristic parameters were obtained by the fit of the VFT-equation to the data and discussed as a function of pore diameter. It was found that the Vogel temperature decreases with increasing pore size.