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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 21: POSTER: Dynamics and Diffusion
CPP 21.3: Poster
Mittwoch, 28. März 2007, 16:00–18:30, Poster B
Molecular dynamics in a glass-forming liquid crystal as studied by broadband dielectric and thermal spectroscopy — Ana Brás1, Madalena Dionísio1, Heiko Huth2, Christoph Schick2, and •Andreas Schoenhals3 — 1REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa, P-2829-516 Caparica — 2University of Rostock, Department of Physics, Universitätsplatz 3, D-18051 Rostock — 3Federal Institute of Materials Research and Testing, Unter den Eichen 87, D-12205 Berlin
Broadband dielectric (10 mHz to 1GHz) and thermal spectroscopy (1 mHz to 10 kHz) was employed to study the molecular dynamics of the nematic liquid crystalline mixture E7. In agreement with theoretical considerations the dielectric spectra shows two relaxation processes. The process at lower frequencies is due to hindered rotational fluctuations about the short molecular axis (delta-relaxation) of the molecules. The process at higher frequencies is related to librational fluctuations around the long molecular axis (tumbling modes). The temperature dependence of the relaxation rate for the delta-process and the tumbling in the nematic phase obey the empirical Vogel-Fulcher-Tamman behavior which is typical for glass-forming systems. For the first time it was shown that the temperature dependence of the relaxation rates for the delta-process and the tumbling modes is essential different using a derivative technique. The comparison of the dielectric with the thermal data gives the result that the glass transition in this system corresponds to the tumbling mode.