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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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