Collective and molecular dynamics in low molar mass and polymeric ferroelectric liquid crystals
作者:
A. Schönfeld,
F. Kremer,
R. Zentel,
期刊:
Liquid Crystals
(Taylor Available online 1993)
卷期:
Volume 13,
issue 3
页码: 403-412
ISSN:0267-8292
年代: 1993
DOI:10.1080/02678299308026313
出版商: Taylor & Francis Group
数据来源: Taylor
摘要:
By use of a novel sample preparation technique, it is possible to measure with one sample cell the collective and molecular dynamics (10−1Hz-109Hz) of macroscopically (in bookshelf geometry) oriented ferroelectric liquid crystals. Below 106Hz, two ferroelectric modes, Goldstone- and soft-mode, are observed, being assigned to fluctuations of the phase and amplitude of the helical superstructure respectively. Between 106and 109Hz, one dielectric loss process exists, theβ-relaxation which originates from the librational motion (hindered rotation) of the mesogen around its molecular long axis. This process does not split or broaden at the non-ferroelectric-ferroelectric phase transition and it has an Arrhenius type temperature dependence. In comparing a racemic mixture with a chiral sample, it performs a similar frequency and temperature dependence. The experimental findings for theβ-relaxation are in qualitative contrast to the predictions of the (generalized) Landau expansion of the free energy at the non-ferroelectric-ferroelectric phase transition. The experiment also leads to a modified understanding for the molecular origin of ferroelectricity in FLCs.
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