Berlin 2008 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 30: Polymerphysics II
CPP 30.11: Talk
Thursday, February 28, 2008, 16:45–17:00, C 130
Dynamics of n-alkyl-cyanobiphenyl and cyano-n-alkylbenzoate molecules in a surface layer adsorbed onto aerosil — Stefan Frunza1, Ligia Frunza1, and •Andreas Schönhals2 — 1National Institute of Materials Physics, R-077125 Magurele, Romania — 2Federal Institute of Materials Research and Testing, D-12205 Berlin, Germany
Composites prepared from aerosil and n-alkyl-cyanobiphenyl (nCB, n=2 - 8) or cyano-n-alkylbenzoate (CPnB; n= 4 - 7) molecules are investigated by dielectric spectroscopy (10 mHz to 1 GHz) in a large temperature range. The selected high silica density allows the observation of the behavior of a thin layer (with nearly a one or two-monolayer structure) adsorbed on the silica particles. For the composites one relaxation process is observed at frequencies much lower than that of the processes found for the corresponding bulk. It is assigned to the dynamics of molecules in a surface layer. The temperature dependence of its relaxation rates obeys the Vogel/Fulcher/Tammann law, characteristic for glassy dynamics liquids. For both systems they vary continuously with the length of alkyl chain. This is discussed in detail in the frame work of quasi two-dimensional character of glassy dynamics of molecules adsorbed on a surface.