Dielectric relaxation in carbosilane dendrimers with cyanobiphenyl end groups |
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Authors: | B Trahasch H Frey K Lorenz B Stühn |
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Institution: | Fakult?t für Physik Albert-Ludwigs-Universit?t Hermann-Herder-Strasse 3 D-79104 Freiburg, Germany, DE Institut für Makromolekulare Chemie und Freiburger Materialforschungszentrum Stefan-Meier-Strasse 21/31 D-79104 Freiburg, Germany, DE Technische Physik II/Polymerphysik TU-Ilmenau, Postfach 100565 D-98684 Ilmenau, Germany e-mail: bernd.stuehn@physik.tu-ilmenau.de Tel.: +49-3677-693671 Fax: +49-3677-693770, DE
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Abstract: | Carbosilane dendrimers of generation 1 and 2 are functionalized with mesogenic end groups (cyanobiphenyl) via spacers of
5 and 11 carbons. The dielectric relaxation is measured over broad frequency (1 Hz–1 GHz) and temperature (170–470 K) ranges.
Two relaxation regimes are observed and characterized as δ and β relaxation. The δ relaxation is nearly a single Debye process
and varies strongly with temperature. The SE to SA transition observed for the dendrimers with long spacers causes a jump in the relaxation rate of the δ process. The β process
displays an Arrhenius-type temperature dependence with an activation energy of 35 kJ/mol. The relaxation time depends on spacer
length. The dielectric relaxation reflects the mutual distortion of the dendrimer scaffold and the smectic layers.
Received: 9 June 1999 Accepted in revised form: 21 July 1999 |
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Keywords: | Dendrimers Dielectric spectroscopy |
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