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Dielectric relaxation in carbosilane dendrimers with perfluorinated end groups

Trahasch, B. and Stühn, B. and Frey, H. and Lorenz, K. (1999):
Dielectric relaxation in carbosilane dendrimers with perfluorinated end groups.
32, In: Macromolecules, (6), pp. 1962-1966, [Article]

Abstract

A series of carbosilane dendrimer generations GxRF6 (x = 1, 2, 3) with perfluorohexyl (-C6F13) end groups as well as an unmodified G3 with allyl end groups has been investigated using dielectric spectroscopy. The experiments comprised a frequency range from 2 Hz to 1 GHz. The dendrimers show a fast (beta) relaxation with an Arrhenius type temperature dependence and an activation energy of 17 kJ/mol. The dominant alpha-process is found in all GxRF6 dendrimers and is split into a slow and a fast part. Its temperature dependence is the same for generation 1 and 2. At elevated T both components apparently merge. Microscopically they are related to the existence of dipole components parallel and perpendicular to the long axis in the end group. The nematic field splits the relaxational dynamics into two components. For G1RF6 a transition from a smectic to a nematic slate is observed at T = 15 degrees C. It is observed in the dielectric relaxation as a discontinuous increase of the relaxation times for both components of the alpha-process.

Item Type: Article
Erschienen: 1999
Creators: Trahasch, B. and Stühn, B. and Frey, H. and Lorenz, K.
Title: Dielectric relaxation in carbosilane dendrimers with perfluorinated end groups
Language: English
Abstract:

A series of carbosilane dendrimer generations GxRF6 (x = 1, 2, 3) with perfluorohexyl (-C6F13) end groups as well as an unmodified G3 with allyl end groups has been investigated using dielectric spectroscopy. The experiments comprised a frequency range from 2 Hz to 1 GHz. The dendrimers show a fast (beta) relaxation with an Arrhenius type temperature dependence and an activation energy of 17 kJ/mol. The dominant alpha-process is found in all GxRF6 dendrimers and is split into a slow and a fast part. Its temperature dependence is the same for generation 1 and 2. At elevated T both components apparently merge. Microscopically they are related to the existence of dipole components parallel and perpendicular to the long axis in the end group. The nematic field splits the relaxational dynamics into two components. For G1RF6 a transition from a smectic to a nematic slate is observed at T = 15 degrees C. It is observed in the dielectric relaxation as a discontinuous increase of the relaxation times for both components of the alpha-process.

Journal or Publication Title: Macromolecules
Volume: 32
Number: 6
Divisions: 05 Department of Physics > Institute for condensed matter physics
05 Department of Physics
Date Deposited: 27 Feb 2010 12:50
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