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Tilt Angle Variation as a Function of Chain Length and Temperature in the Smectic C Phases ofp, Alkoxyphenyl-p, Alkoxybenzoates

 

作者: B. Heinrich,   D. Guillon,  

 

期刊: Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals  (Taylor Available online 1995)
卷期: Volume 268, issue 1  

页码: 21-43

 

ISSN:1058-725X

 

年代: 1995

 

DOI:10.1080/10587259508030990

 

出版商: Taylor & Francis Group

 

数据来源: Taylor

 

摘要:

The variation of the tilt angle with temperature in the smectic C phase has generally been shown to be non-existent or very slow for compounds or mixtures with the nematic-smectic C transition, while in the case of systems with the smectic A- smectic C transition, a relation between the steepness of this variation, near the transition, and the width of the smectic A domain has been observed. In this work, the variation of tilt angle in the smectic C phase is described forp-alkoxyphenyl-p-alkoxybenzoate homologous series, for which the evolution of polymorphism can be controlled systematically, by varying stepwise the length of the aliphatic chains, and for which large domains can be obtained for each type of phase sequence, nematic-, smectic A- and isotropic- smectic C. After completing the discussion made previously on the incidence of chain length on polymorphism, we confirm that the variation of tilt angle with temperature is slowest for compounds with intermediate chain lengths corresponding to the largest smectic A temperature range; this variation becomes continuously steeper when the smectic A domain becomes narrow. In addition, we show that the same description can be extended to the other types of phase sequences, by using the hypothesis of a virtual smectic A-smectic C transition above the observed nematic- or isotropic-smectic C transition. In fact, short chain lengths for homologues with a nematic/smectic C transition, or long chain lengths for homologues with an isotropic/smectic C transition, lead to an increase of the tilt angle at the phase transition and to a decrease of the amplitude of its variation with temperature; in our description, this behaviour corresponds to an increase of the temperature range between the real and virtual transitions. As a consequence, the homologues with very short and very long chain lengths show a quasi temperature-independent tilt angle, while the other homologues present a tilt angle variation similar to that observed for compounds exhibiting a smectic C/smectic A transition. This feature indicates that there is no need to distinguish between different types of smectic C phase.

 

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