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From monomeric to polymeric ferroelectric liquid crystals A comparative study of ferroelectric properties

 

作者: Holger Poths,   Erik Wischerhoff,   Rudolf Zentel,   Axel Schönfeld,   Guido Henn,   Friedrich Kremer,  

 

期刊: Liquid Crystals  (Taylor Available online 1995)
卷期: Volume 18, issue 5  

页码: 811-818

 

ISSN:0267-8292

 

年代: 1995

 

DOI:10.1080/02678299508036694

 

出版商: Taylor & Francis Group

 

数据来源: Taylor

 

摘要:

Two new ferroelectric oligosiloxanes, a cyclic tetramer and a twin, have been synthesized. By a comparative study with their corresponding monomer and side chain polysiloxanes, the influence of oligo- and polymerization on the liquid crystalline and ferroelectric properties have been investigated. Polymerization leads to a stabilization of LC phases through increase of the clearing temperatures and suppression of crystallization. Oligomerization also leads to mesophase broadening, but, due to the low degree of polymerization, the effect is inferior to the linear polysiloxanes. The low viscosity of the oligosiloxanes ensures response times in the microsecond region, thus being comparable with their monomer and conventional LMWFLCs. It is found that polymerization increases the spontaneous polarizationPs. This is attributed to the density increase after polymerization, enhancing the inter-mesogenic interactions. The collective and local dynamics of the OFLCs are influenced differently with respect to their molecular structures. Each oligomer is already a good model for its corresponding polymer concerning the soft mode dynamics. For the local β-relaxation a similar temperature dependence of the relaxation times τ for the cyclic tetramer and for the side chain polysiloxanes is observed. The long axial rotation of the twin, having a very efficient decoupling, is significantly faster, thus resembling the monomer.

 

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